Contents

Chapter 1 BASICS OF SEALING

1.1 Sealing1.2 Basics of sealing

Chapter 2 MECHANICAL SEALS

2.1 Mechanical Seal 2.2 The Basic Mechanical Seal2.3 How a Mechanical Seal Works

Chapter 3 MECHANICAL SEAL TYPES

3.1 Pusher Type3.2 Unbalanced 3.3 Conventional 3.4 Non Pusher 3.5 Balanced3.6 Cartridge

Chapter 4 SELECTING METAL PARTS OF THE SEAL

4.1 Metal and Non Metal parts Of the Seal4.2 Choosing The Seal Face combination4.3 Selecting The Correct hard face

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Contents[cont.d]

Chapter 5 ENVIRONMENTAL CONTROL

5.1 Seal Application Problems 5.2 Controlling The Pressure In The Stuffing box Area

Chapter 6 TROUBLESHOOTING OF MECHANICAL SEALS

6.1 Reasons of Seal failure6.2 Inspection of individual components

6.2.1 The Carbon Face 6.2.2 The Hard Face 6.2.3 The Elastomer 6.2.4 The metal Case

6.2.5 The Springs 6.2.6 The Sleeve 6.2.7 Set Screw 6.2.8 The Gland 6.2.9 Bushing

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CHAPTER 1Basics of Sealing

1.1 Sealing In rotating equipment the required rotational mechanical energy is either input or output. In both cases clearances are to be provided for smooth rotation of shafts and other mechanical power transmitting components, these clearance are the passages from where the working medium of the process can leak out, the process of preventing such leakage is called sealing.

1.2 Basics of Sealing There are two kinds of seals: static and dynamic. Static seals are used where no movement occurs at the location to be sealed. Gaskets and O-rings are examples of static seals.

When surfaces move relative to each another the seals used are called dynamic seals. for example, where a rotating shaft transmits power through the wall of a tank (Fig. 1.1), through the casing of a pump (Fig. 1.2), or through the housing of other rotating equipment such as a filter or screen.

Fig. 1.1 Cross Section of Tank and Mixer

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Fig. 1.2 Typical Centrifugal Pump

A common application of sealing devices is to seal the rotating shaft of a centrifugal pump. (Figures 1.3 and 1.4).

Fig. 1.3 Centrifugal Pump, Liguid End

Fig.1. 4 Fluid Flow in Centrifugal Pump

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As the impeller vanes rotate, the liquid leaves the impeller, under pressure through the pump discharge. Discharge pressure will force some liquid to escape along the rotating shaft, seals are necessary to limit the escape of the product to the atmosphere. Such sealing devices are typically either packing or mechanical seals.

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CHAPTER 2Mechanical Seals

2.1 Mechanical Seals A mechanical seal is a device which forms a running seal between rotating and stationary parts. Advantages of mechanical seals over conventional packing are as follows:

1. Limited leakage of liquid 2. Reduced Power loss. 3. Less shaft or sleeve wear. 4. Reduced maintenance costs. 5. Ability to seal higher pressures and corrosive environments. 6. The wide variety of designs allows use of mechanical seals in almost all rotating

equipment applications.

2.2 The Basic Mechanical Seal All mechanical seals are constructed of three basic parts as shown in Fig. 2.1:

1. A set of primary seal faces: one rotary and one stationary…see Fig. 2.1, seal ring and insert.

2. A set of secondary seals known as shaft packings and insert mountings such as 0-rings, wedges and V-rings.

3. Mechanical seal hardware including gland rings, collars, compression rings, pins, springs and bellows.

Fig. 2.1 Simple Mechanical Seal

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2.3 How A Mechanical Seal Works

The primary seal is achieved by two very flat, lapped faces, the rubbing contact between these two flat mating surfaces do not allow the liquid or gas to pass through and thus minimizes leakage. As in all seals, one face is held stationary in a housing and the other face is fixed to, and rotates with, the shaft. One of the faces is usually a non-galling material such as carbon-graphite. The other is usually a relatively hard material like silicon-carbide. Dissimilar materials are usually used for the stationary insert and the rotating seal ring face in order to prevent adhesion of the two faces. The softer face usually has the smaller mating surface and is commonly called the wear nose.

There are four main sealing points within an end face mechanical seal (Fig. 2.2). The primary seal is at the seal face, Point A. The leakage path at Point B is blocked by either an 0-ring, a V-ring or a wedge. Leakage paths at Points C and D are blocked by gaskets or 0-rings.

Fig. 2.2 Sealing Points for Mechanical Seal

The faces in a typical mechanical seal are lubricated with a boundary layer of gas or liquid between the faces.

To select the best seal design, it's necessary to know about the operating conditions and the product to be sealed. Thorough information about the product and environment will allow selection of the best seal for the application.

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CHAPTER 3Mechanical Seal Types

3.1 PUSHERTYPE: A typical 'pusher type' mechanical seal figure 2.3a & b, consists of a rotating face, a stationary face and secondary sealing elements with adaptive metal parts such as a flange and a sleeve. The stationary face is seated in a flange which is bolted onto the pump cover. For most seals the rotating face can move in the axial direction and is kept in place by a spring holder and one or more springs. The rotating parts are installed on a shaft sleeve or directly on the shaft. The gasket that can move axially with the rotating face is called a 'dynamic' gasket. The secondary sealing elements are often elastomers, but by special design PTFE can also be used. Figure 2.4 shows a typical pusher type seal as available in the market.

Figure 3.1 aParts of a pusher type seal

Figure 3.1 bProduct flow in a pusher type

seal

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The pusher seals' advantage is that it's inexpensive and commercially available in a wide range of sizes and configurations. Its disadvantage is that it is prone to secondary seal hang-up and fretting of the shaft or sleeve.

3.2 UNBALANCED: They are inexpensive, leak less, and are more stable when subjected to vibration, misalignment, and cavitation. The disadvantage is their relative low pressure limit. If the closing force exerted on the seal faces exceeds the pressure limit, the lubricating film between the faces is squeezed out and the highly loaded dry running seal fails. Examples are the Dura RO and Crane 9T.

Figure 3.3

Figure 3.2A typical pusher type seal

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Figure 3.4 Unbalanced.conical sping

Figure 3.5 Single spring unbalanced

Figure 3.6

3.3 CONVENTIONAL: Examples are the Dura RO and Crane Type 1 which require setting and alignment of the seal (single, double, tandem) on the shaft or sleeve of the pump. Although setting a mechanical seal is relatively simple, today’s

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emphasis on reducing maintenance costs has increased preference for cartridge seals.

3.4 NON-PUSHER: The non-pusher or bellows seal does not have to move along the shaft or sleeve to maintain seal face contact, The main advantages are its ability to handle high and low temperature applications, and does not require a secondary seal (not prone to secondary seal hang-up). A disadvantage of this style seal is that its thin bellows cross sections must be upgraded for use in corrosive environments. Bellow type mechanical seal is very similar to pusher, but uses a welded metal bellows to achieve flexibility in the design. A bellows seal avoids the use of a ‘dynamic’ gasket, which allows the use of grafoil for high temperature applications.

Figure 3.7

Bellow

Bellow

Figure 3.8

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Figure 3.9 b

Figure 3.9 c

3.5 BALANCED: Balancing a mechanical seal involves a simple design change, which reduces the hydraulic forces acting to close the seal faces. Balanced seals have higher-pressure limits, lower seal face loading, and generate less heat. This makes them well suited to handle liquids with poor lubricity and high vapor pressures such as light hydrocarbons. Examples are Dura CBR and PBR and Crane 98T and 215.

Figure 3.9 aPrinciple of action of a bellow type seal

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Figure 3.10

3.6 CARTRIDGE: Examples are Dura P-SO and Crane 1100 which have the mechanical seal premounted on a sleeve including the gland and fit directly over the Model 3196 shaft or shaft sleeve (available single, double, tandem). The major benefit, of course is no requirement for the usual seal setting measurements for their installation. Cartridge seals lower maintenance costs and reduce seal setting errors.

Diagrams showing some typical seal assemblies-

Figure 3.11Clamped seat

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Figure 3.12 O- Ring Seat

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CHAPTER 4Selecting Metal Parts of The seal

4.1 Metalic and Non metallic parts of the Seal

If the pump's wetted parts are manufactured from a non-metallic material such as Teflon®, Kynar, Polyethylene, etc. we choose non-metallic seal components.

Figure 4.1

The above illustrations describe two seal designs that operate with no metal parts exposed to the sealing fluid. Please note that in both cases the seals are clamped, not set-screwed to the shaft. You cannot use sets-crews in these designs because non-metallic seals are often used on glass coated shafts.

If the wetted parts of the seal are manufactured from iron, steel, stainless steel or bronze, and they are not showing signs of corrosion, the seal components (with

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the exception of the springs) can usually be manufactured from grade 316 Stainless Steel.

The springs must be manufactured from “Hastelloy C” or a similar corrosion resistant material to avoid the problems associated with Chloride Stress Corrosion and the 300 series of stainless steel.

There are exceptions to all general rules however, and it turns out that there are a number of places we cannot use grade 316 stainless steel seal components successfully and yet iron, steel, other grades of stainless steel or bronze are usually satisfactory.

The following list describes some of those chemicals and identifies the metal normally selected by the equipment manufacturer for chemical resistance. Keep in mind that temperature, concentration, stress etc. affect the chemical resistance of any material, so check with someone knowledgeable before you specify any metal components.

CHEMICAL METAL

Aroclor Bronze Bronze

Barium Carbonate Bronze

Benzene Carbon Steel or Bronze

Benzene, Hot Bronze

Bromine Gas Bronze

Calcium Carbonate 303/304 Stainless

Phenol (Carbolic Acid) 303/304 Stainless

Butyl Phthalate Bronze

Dichlorodifluoromethane (F12) 303/304 Stainless

Diethyl Ether 430 Stainless

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Ethanol Bronze

Ethanolamine 303/304 Stainless

Fluorine Gas, Dry 430 Stainless

Hydrogen Chloride Gas, Wet Carbon Steel

Magnesium Sulfate 303/304 Stainless

Monoethanolamine 303/304/430 Stainless

Mixed Acids Bronze

Nickel Chloride 303/304 Stainless

Nuclear Primary Water Systems 304 Stainless

Potassium Bicarbonate 303/304 Stainless

Potassium Chlorate 303/304 Stainless

Potassium Hydrate 303/304/430 Stainless

Potassium Oxalate Bronze

Potassium Permanganate Bronze

Pyrogallic Acid Bronze

Sodium Benzoate Bronze

Sodium Bichromate Bronze

Sodium Bromide Bronze

Sodium Chlorate Bronze

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Sodium Citrate Bronze

Sodium Dichromate Bronze

Sodium Ferricyanide Bronze

Sodium Fluoride Bronze

Sulfuric Acid Carbon Steel or 430 Stainless

Titanium Tetrachloride Carbon steel

Uric Acid Bronze

If you have any doubt about the compatibility of 316 Stainless Steel with your pump, you can check your facility for any experience you might have with 316 stainless parts in a similar service. If no such experience exists and you are uncomfortable making the selection, contact a qualified metallurgist.

As an additional matter of interest the material we refer to as grade 316 stainless steel is made from the following ingredients:

Chrome 18-20 % Nickel 8-12 % Carbon 0.08 % Iron 64-70 % Silicone 1% Manganese 2% Sulphur 0.030 % Phosphorous 0.045 %

The designation 316 stainless steel is not used in all countries. The following list shows the designations used by some other nations for a similar product:

Germany 1.4571 or V4A England EN58J Sweden 2343 Hungary KO35 Czechoslovakia 17246 

4.2 CHOOSING THE SEAL FACE COMBINATION

SELECTING THE CARBON/ GRAPHITE FACE

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The most common face combination you will be selecting is a good grade of carbon-graphite running against a corrosion resistant hard face. The seal face we refer to as a carbon is really a compound of carbon and graphite. We use graphite for its lubricating qualities and good heat conductivity. We use the carbon for its corrosion resistance and strength.

With few exceptions mechanical seal companies purchase carbon-graphite molded faces from one of several carbon manufacturers. The seal companies pay for the necessary molds and then retain the exclusive use of them. A really good seal face would be a mixture of carbon, graphite and nothing else.

The carbon is purchased as a by-product of a manufacturing process while the graphite is mined with the main sources being in Canada and Madagascar. Two things determine the cost of these elements:

How finely is the product milled? A fine talc is desirable. How pure is the product? There will always be some impurities, but the fewer the better

because these impurities could possibly present a chemical compatibility problem and a difference in face density.

A good carbon-graphite mixture would be about 80% carbon and 20% graphite. Graphite is a good conductor of heat, a natural lubricant and has a laminar grain structure similar to a deck of playing cards allowing the individual grains to slide over one another. It is this laminar structure that allows the graphite to release from the carbon/ graphite face and deposit on the hard face in the same manner a graphite pencil will write on a sheet of paper.

Carbon is a very different element. It is manufactured by heating an organic material (it once was alive) to 2000 degrees Fahrenheit (1000°C). It is not a very good conductor of heat and is a poor lubricant because of its crystal structure. If carbon is heated to 4000 degrees Fahrenheit (2000°C) under pressure, it will convert to graphite.

To manufacture the finished product we place this carbon-graphite mixture in an oversized mold using a hydrocarbon as the glue to hold the powder together. The mixture is then compressed and placed in an oven at 2000° Fahrenheit (1000° C) for a period of thirty to sixty days. The hydrocarbon will convert to carbon at this temperature. The piece must be heated slowly or otherwise the carbon will combine with oxygen to form carbon monoxide or carbon dioxide, which will in either case ruin it. At the end of this time the piece has shrunk a small amount but still resembles a real carbon face. The problem is:

It has poor tensile strength It has low heat conductivity because the mixture is very porous. It has low density that would present a problem in vacuum applications, as well as

pharmaceutical and food products because of the difficulties in cleaning the lapped seal faces..

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At this point any inorganic (it never lived) material can be imbedded into the carbon/graphite shape. If you should use such an impregnation you would have to be concerned about the chemical compatibility of the filler material with the product you are trying to seal. Metal salts are inorganics frequently used by some manufacturers.

If you want a serious carbon you must place the component into a tank like appatatus called an autoclave, where a vacuum will remove impurities that may have imbedded into the porous face. The autoclave will then be filled with a liquid hydrocarbon and pressurized to force the hydrocarbon into the porous face under high pressure. In the old days the hydrocarbon was “pitch” from a tree but in modern times a variety of hydrocarbons are available.

This first impregnation will penetrate approximately 25 mm. (one inch) meaning that 50 mm (2 inches) will be impregnated if the hydrocarbon can penetrate from all sides of the shape. The face is then placed back into the oven and fired at 2000° Fahrenheit (1000 C.) for an additional 30 to 60 days where the impregnate is converted to carbon. There is also a certain amount of shrinking that takes place during this converting process.

You now have a denser carbon/graphite, but you are a long way from a good one. Two more impregnations at 3,0 mm. (0.125 inches) and 0,5 mm (0.020 inches) will complete the impregnations, each taking 30 to 60 days in the oven.

About this time you hit a point of diminishing returns, so the third impregnation is pushed into the carbon/graphite, but not fired in the furnace. This type of seal face is referred to as an “unfilled carbon and is available from several manufacturers both in the United States and abroad.

Figure 4.2

C = 25,0 mm (1 inch) impregnation B = 3,0 mm (0.125 inches) impregnation A = 0,5 mm (0.020 inches) impregnation

As shown in the diagram, the last impregnate will wear away from the seal face, but will remain on the outside and inside diameters providing the density the face needs to hold

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vacuum and provide the surface needed to prevent bacteria and other un-desirable elements from penetrating into the composite.

If a seal manufacturer needs a only a few seal faces for test purposes he can machine them out of a good grade of unfilled carbon and then send them back to the carbon manufacturer for the final impregnations. Small batch applications are handled like this also.

When ever possible carbon-graphite is the face that should be the standard in all of your mechanical seals. It can be used in any chemical or combination of chemicals except an oxidizing agent, a halogen and some special applications.

As mentioned, the oxidizing agents will combine with the carbon to form carbon dioxide and carbon monoxide. Here is a list of some of the common oxidizers:

Aqua Regia (a combination of nitric and hydrochloric acid) used for dissolving metals. Chloric acid ignites organic material on contact. Chlorous acid, over 200 degrees Fahrenheit (100 C). Ferric chloride used in sewage treatment photography, medicine and feed additives. Hot sulfuric acid, the most widely used industrial chemical. Hydrofluoric acid used for etching, cleaning castings and fermentation. Methyl Ethyl Ketone (MEK) a common solvent. Nitric acid used in fertilizer, dyeing, explosives, drugs, etching and medicine. Oleum used in the manufacture of detergents and explosives. Perchloric Acid - 2N Perchloric acid used in the manufacture of medicine, explosives, and esters. Sodium hypochlorite, used in bleaching paper pulp, textiles, and tanning textiles. Sulfur trioxide used to manufacture sulfuric acid.

Additionally look for any chemical whose name contains the word:

Chlorate Nitrate Perchlorate Permanganate Peroxide

The Halogens are another group of chemicals that will attack carbon. They are easy to identify because their chemical name ends in the letters "ine":

Astintine Bromine Chlorine Fluorine Iodine

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The oxidizer's chemical concentration and temperature will affect the degree of attack. If you are handling any of these chemicals or any chemical you suspect might attack carbon, it would pay to test an unfilled carbon for compatibility prior to installing a mechanical seal.

Immerse the carbon into the liquid and leave it there for a reasonable period of time. A couple of weeks should be enough in most cases.

Recent experience shows that all grades of carbon are no longer being recommended in the following applications:

If there is a possibility of color contamination of the product. Some paper, pharmaceutical and paint applications have this potential color problem.

If you are sealing hot oil and have to meet fugitive emission standards. Some de-ionized water applications can attack carbon.

Original equipment manufacturers (OEM) use filled carbon in their seals, and as a result you end up with a spare parts problem. It is not unusual to find five similar seals, with five different part numbers and the only difference between them are the grades of carbon/ graphite.

Cryogenic service uses a special carbon that has some inorganic compounds added to compensate for the fact that adsorbable gases or vapors are not present to weaken the interlacing bonding forces between the carbon and the graphite. It is these adsorbable gases and/ or vapors that allow the graphite to release from the compound and coat the hard surface with a low friction-lubricating layer.

Children recognize this problem when they lick the end of a graphite pencil to make the writing darker.

Most sealing applications can be satisfied with an unfilled carbon running against one of several hard faces. You should contact the carbon manufacturers for their catalog showing you the grades they have available and the physicals (specifications) of their unfilled carbon. You can then check with your seal supplier to be sure he is using the proper unfilled grade in your mechanical seals.

A carbon company can provide several unfilled grades depending upon the number of impregnations (density) and special characteristics, such as the ability to fracture without producing many dust particles. This is an important characteristic in some split seal designs.

I have included a typical specification chart for you. It is a reproduction of a page from the advertising literature of the Pure Carbon Company of St. Marys, Pennsylvania, USA. Their grade P658RC would be a typical unfilled carbon.

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You can locate these carbon companies on the "Web" or find them in various technical directories such as the Thomas Register in the United States.

Now that we know which carbon-graphite to use we can look at the hard faces that are available to us.

4.3 SELECTING THE CORRECT HARD FACE MATERIAL

The ideal hard face material would incorporate many features including the following:

Excellent corrosion resistance. Self-lubricating. High strength in compression, shear and tension. High modulus of elasticity to prevent face distortion. Good heat conductivity. Good wearing characteristics (hardness). High temperature capability. Temperature cycling capability. Easy insertion into a metal holder Low coefficient of friction. The ability to be molded in thin cross-sections.

Needless to say all of these characteristics are not available in the same face material. The idea is to get as many of them as you can in a properly chosen face combination.

With just a few exceptions seal companies purchase hard face materials from outside vendors. Be sure the face component you choose is identified by material, type and grade so that you can check out the physicals. Some companies change the generic name of the material to confuse you. Make sure you know exactly what you are purchasing or you will never be able to trouble shoot a seal failure caused by a wrong material selection.

Take a look at the chart labeled: "HARD FACE MATERIALS" This chart lists the physicals for some of the most common hard face materials used in the mechanical seal industry. Most of the information was supplied by the Pure Carbon Company of St. Mary's, Pennsylvania.

Use these numbers only as a guide. Individual manufacturers use different testing methods and express the results in different metric and imperial units. I have also listed some of the hard face manufacturers so that you can contact them directly for test results, latest specifications, newer materials, availability, etc.

There is some additional information you should know about the materials listed in the chart:

Reaction bonded silicon carbide

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Reaction bonded silicon carbide is produced by adding molten silicon to a mixture of silicon carbide and carbon. A reaction between the silicon and carbon bonds the structure while the excess silicon metal fills the majority of the pits left in the resultant material. There is almost no shrinkage during the process.

The silicon content is about 8% to 15%. Be aware that high pH chemicals such as caustic can attack this grade of silicon carbide.

As of this writing carbon-graphite vs. reaction bonded silicon carbide has been demonstrated to have the best wear characteristics of all the possible face combinations.

Reaction bonded silicon carbide is difficult to insert into a metal holder so it is usually supplied in a solid rather than a composite configuration.

There are many manufacturers of reaction bonded silicon carbide. The following chart shows some of them.

COMPANY DESIGNATION

Carborundum KT

BNFL Refel

Coors SC-2

Norton HD-630

Pure Carbon PS-9242

ESK, Shunk and Hoechst of West Germany are also manufacturers of reaction bonded silicon carbide.

Reaction bonded silicon carbide has proven to be more chip resistant than the sintered version

Avoid the following hifg pH chemicals when using reaction bonded silicon carbide :

o Sodium Hydroxide o Potassium Hydroxide o Nitric Acid * o Green Sulfate Liquor * o Calcium Hydroxide * o Hydrofluoric Acid o Caustics and strong acids o Most high pH chemicals

* Results vary with temperature and concentration.

The above chemicals can leach the silicon out of the silicon carbide leaving a weakened, hard matrix that can act like a grinding wheel against the softer carbon face.

Self sintered silicon carbide (sometimes called Alpha sintered, direct sintered or pressure less sintered)

This material begins as a mixture of silicon carbide grains and a sintering aid that is pressed and subsequently sintered as its name implies. Unlike reaction

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bonded SiC there is no free silicon present. These direct sintered materials have no metal phase and are therefore more resistant to chemical attack.

There are two grain shapes available to the manufacturer. Alpha (hexagonal structure) and Beta (cubic structure). There does not appear to be any great difference in the chemical resistance, wear or friction of these two grain shapes.

Most process chemicals will not attack these self sintered materials. In the following box you will find some of the bigger manufacturers of self sintered silicon

carbide:

COMPANY DESIGNATION

Carborundum SA-80

General Electric Sintride

Kyocera SC-201

Sintered silicon carbide is almost impossible to shrink into a metal holder. Self-sintered silicon carbide carries a slight price premium compared to the

reaction bonded version. Although the preferred seal face material, it often is too brittle for some seal face

designs using thin cross section components.

Siliconized graphite

The manufacturing process uses a permeable form of carbon graphite that is reaction sintered in silicon at elevated temperature. This forms an outer layer of silicon carbide on the graphite base.

A resin impregnate is added to increase the density.

Tungsten Carbide

Cobalt and nickel are the common binders used to hold the tungsten particles together. Each is susceptible to selective chemical attack of this metallic binder that will leave a skeletal surface structure of tungsten carbide particles.

Galvanic corrosion can take place between a passivated stainless steel shaft or seal face holder and the active nickel in the nickel base tungsten carbide seal face. This can be a real problem in caustic and other high pH fluids. The temperature at the seal face is higher than the temperature of the sealing fluid so the attack takes place quicker.

The metallic binders in tungsten carbide are also subject to galvanic attack near copper, brass or bronze.

Tungsten carbide is less difficult to insert into a metal holder so it is the most common material used in metal bellows and other hard face metal composite designs.

Here are some additional thoughts about hard seal faces:

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Many sales people promote two hard faces running against each other as the ideal face combination for slurry and similar services. Keep in mind that solids cannot penetrate between seal faces unless they open. Seal faces are lapped to a flatness of less than one micron (three helium light bands) and as long as they stay in contact solids are filtered out. Here are some of the main disadvantages of using two hard faces in a seal application:

o Higher cost compared to using carbon-graphite as a seal face. o If either face is "out of flat" it is almost impossible for the faces to lap

themselves back together again. o Carbon graphite provides an additional lubricating film if you are sealing a

poor or non-lubricating fluid. It should be noted that many fluids fall into that category. It takes a film thickness of at least one micron at operating temperature and face load to be classified as a lubricating fluid. Without this lubricating fluid you will generate undesireable heat at the seal faces

o Carbon graphite can easily be inserted into a metal holder. o In the event the equipment is "run dry" carbon/ graphite is self-lubricating.

Use two hard faces in the following applications: o If you are sealing hot oil or almost any hot hydrocarbon. Most oils coke

between the seal faces and can pull out pieces of carbon causing fugitive emissions problems.

o If the product tends to stick the faces together. o If the product you are sealing is an oxidizer that will attack all forms of

carbon, including black O-rings. Oxidizing chemicals are listed in another section of this manual.

o Halogens can attack all forms of carbon. These Halogen fluids include: chlorine fluorine bromine astintine iodine

o If you are pumping a slurry and you cannot keep the two lapped faces together by flushing with a clean liquid, suction recirculation, a large diameter stuffing box or some other method usually employed to seal a large percentage of solids.

o If nothing black is allowed in the system because of a possible color contamination of the product you are pumping.

o Some deionized (DI) water applications can attack any form of carbon. Hard faces have their own problems:

o Plated or coated faces can "heat check" and crack due to the differential expansion of the coating and the base material.

o Sometimes PV numbers dictate the use of two hard faces. Keep in mind that PV (pressure x velocity) factors as a design tool are unreliable because carbon is sensitive to "P" but not to "V".

o Hot water can cause cracking problems with both 85% and 99.5% ceramic. The cause is not fully understood, but hydrogen embrittlement is

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suspected as the culprit. Cracks have been observed after seven to eight temperature cycles. Because hot water is often a non-lubricant you can develop "slip stick" vibration problems.

Unfilled carbon should be your first choice for a material to run against the above mentioned hard faces. Use an unfilled carbon in all applications except in those applications that require two hard faces and:

Cryogenic and dry running applications require a special carbon with an embedded organic to release the graphite.

Hot oil if the seal has to meet fugitive emission standards.

4.4  CHOOSING THE CORRECT ELASTOMER

The O-ring selection chart is an attempt to select the fewest number of elastomers that will give you satisfactory sealing. As you can see from the selection, most of the chemicals can be handled by either fluorocarbon (Viton® and Fluorel are typical examples) or ethylene propylene. The following paragraphs describe the codes used in the chart.

V - fluorocarbon. The compound specified is the specific one that has some water immersion capability. Dupont E60 Viton®, 3M Fluorel 2174, Parker 747-75 and Parker V884-85 are typical examples.

E - ethylene propylene C - perfluoroelastomers. Chemraz (a registered trademark of Greene, Tweed &

Co.) or Kalrez® (a registered trademark of E.I. Dupont Dow) are typical examples.

N - neoprene B - buna N Bu- butyl U - Unknown, or unreliable test data. Immersion testing or plant experience is

your best bet. If no elastomer proves to be acceptable a non-elastomer (metal bellows) seal may be your only answer.

Keep in mind that this O-ring selection chart is only a guide to help you in selecting the correct elastomer for your mechanical seal application. It was created from published information, various industry guidelines and many years of practical experience by field sales and engineering people.

Most mechanical seals use at least one dynamic elastomer so even small amounts of swelling or chemical attack is almost always unacceptable. When using this chart please keep the following in mind:

Chemical attack will usually double with a 10°C (18° F) increase in temperature. If the elastomer is located close to the seal face it will see the additional heat that

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is being generated by rubbing friction. Elastomers are poor conductors of heat, so cooling one side of the O-ring does not always allow the lower temperature to conduct to the hot side.

If the chemical name is followed by (*), it is called an oxidizer. Oxidizers spontaneously emit oxygen at either room temperature or under slight heating. The oxygen can then combine with the carbon in mechanical seal faces, or the carbon black used to color O-rings, causing chemical attack. The largest group of oxidizing materials is comprised of peroxides. Hydrogen peroxide and benzoyl peroxide are typical. Permanganates, chlorates and some nitrates are also strong oxidizing agents. These materials additionally constitute a dangerous fire hazard, so two seals may be required.

The chemical concentration and temperature determine the degree of carbon and elastomer attack. The higher the concentration and the higher the temperature, the more likely the attack.

Plant experience is your best protection in elastomer selection, but if you have no experience in handling these chemicals it would be wise to immersion test both the black O&endash;ring and carbon face prior to installing a mechanical seal. Sometimes you can duplicate the operating temperature by placing the test vessel in an oven or on a hot plate when ever practical.

The product you are sealing is often a mixture of several chemicals and/ or may have a trade name. This chart normally shows only individual chemicals so you may have to rely upon plant experience or immersion test to determine compatibility. Most plants have prior experience in handling their chemicals so look for elastomers in other mechanical seals, valves, gages, filters, strainers, hoses, lined pipe, etc.

In most cases Chemraz or Kalrez® will handle the job if there is no plant experience or if immersion testing is not practical. It is always worth a try.

Remember that each of these elastomers has an upper and lower temperature limit. Although the elastomer may be chemically compatible with the sealing fluid it could still fail if the temperature limit is exceeded.

Excessive temperature is usually indicated by a change in weight, shape or appearance of the O-ring. Compression set is often the first indication of high heat followed by a shrinking and hardening of the elastomer. If the stuffing box temperature is too high it will be necessary to cool down the seal area. Using an installed stuffing box heating or cooling jacket is the obvious solution. Keep in mind that quenching or the use of two seals with a cool barrier or buffer fluid between them cools only one side of the o-ring. If cooling is not possible you will have to use a metal bellows or some other type of non-elastomer seal.

ELASTOMER F. TEMPT. RANGE C. TEMPT. RANGE

Fluorocarbon (Viton®) -15 +400° -25 +205°

Ethylene propylene -70 +300° -55 +150°

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Chemraz -20 +450° -30 +230°

Kalrez® 0 +500° -20 +260°

Neoprene -45 +300° 45 +150°

Buna N -65 +225° -55 +105°

Buna S -75 +250° -60 +120°

Solvents, cleaners and steam are often used to flush lines and systems. Be sure the elastomer you choose is chemically and temperature compatible with these solvents, cleaners and steam. Some processes will not allow any thing "black" in the system. White colored O-rings are available for many compounds.

Ethylene propylene rubber (EPR) is a very common elastomer mentioned in this chart. Be aware that EPR is easily attacked by any petroleum product so be careful with the type of lubricant you use to lubricate this elastomer. For all practical purposes silicone grease is probably your safest lubricant, but to be sure check for compatibility. There is a high temperature version of EPR available (500°F or 260°C), but it cannot be used if air or oxygen is present on one side of the O-ring. In other words, the application is limited to the dynamic elastomer on the inboard side of a dual seal application.

Many of the chemicals listed are dangerous. Be sure to use an API (American Petroleum Institute) gland or better still, two mechanical seals in these applications.

Nuclear, food products, and pharmaceutical plants often specify specific grades of elastomers and require cure date information for certain products. If you are working in any of these areas check for a list of approved materials.

The term water does not describe a single product. For instance: o De-ionized and demineralized water have had various ions and minerals

removed and as a result they are constantly trying to replace the minerals as the water moves through the pipes and other hardware. The result is that sometimes the water can attack stainless steel and some seal face materials including carbon. You may have to do some immersion testing to be sure if your choices are satisfactory.

o Water treatment varies with each application. These treatment chemicals and additives can attack some elastomers.

o Condensate often contains dissolved amines that could attack the elastomer.

o Water hardness varies with geographic locations. o Wastewater is liable to be any thing. o The chloride concentration in salt water varies widely.

Ethylene propylene rubber (EPR) is the first choice in most water and water based applications but the variance noted above can cause premature O-ring failure. If you have any doubt about your water conduct an O-ring immersion test prior to installing the mechanical seal.

The four step procedure for selecting the correct elastomer is:

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Look up the chemical in the O-ring selection chart . If your product is not on the list or is a combination of several chemical on the list, go to the next step.

Look around the plant for present or past experience. Look for elastomers in valves, other seals, gages, filters, strainers, etc. If you have no experience with elastomers in this fluid go to step "3".

"Test" is the next step. If possible start with two elastomers of the same compound and immerse only one of them in the fluid and leave it there for one to two weeks. You can then compare that O-ring to the one that was not immersed. If the elastomer is not compatible with the fluid it will change weight, shape or appearance. If the elastomer does not pass this test go to the last step

Chemraz or Kalrez® is usually the end of the line. Check the special elastomers chart. If neither of these materials is satisfactory you will have to use a non-elastomer seal such as a metal bellows design. If a reliable flush is available the elastomer may be compatible with the flush, but remember that if you lose the flushing fluid the product will attack the elastomer.

When you are selecting an O-ring, or any other elastomer shape for your mechanical seal application remember that with the exception of solvents, most chemicals and chemical compounds can be successfully sealed with either ethylene propylene or a good grade of Viton® as the dynamic elastomer.

Most mechanical seal designs incorporate both dynamic and static elastomers.

Dynamic O-rings are required to flex and roll with the shaft movement. This means that a very low shaft squeeze and a smooth shaft finish are important to prevent seal hang up or hysteresis. They must also be free to flex and roll to compensate for mechanical seal face wear.

Static O-rings do not have to move. They are used as a gasket and are a lot more forgiving than dynamic O-rings because a small amount of swell can be tolerated that might even improve their sealing.

There are many elastomer shapes available to you; individual seal companies use wedges, V-rings, U-cups, Quad rings etc, but O-rings have a lot of advantages over these other elastomer shapes in mechanical seal design. As an example:

They can seal both pressure and vacuum. They can flex 0.003 to 0.005 inches (0.08 to 0 0.13 mm) before they roll, and

then they can roll up to half of their diameter, making it a lot easier for the seal faces to follow shaft run out and end play.

O-rings reduce shaft fretting dramatically because of this ability to flex and roll. They are available in a variety of compounds. They are the first shape available when a new compound is introduced. Most of the O-ring compounds are available in a wide range of durometer or

hardness. The average mechanical seal uses a durometer of 75 to 80 (as measured on the shore A scale), but harder durometers are available for high-pressure applications similar to those we find in pipe line sealing.

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The O-ring configuration is usually the first shape available when a new compound becomes available from the manufacturer.

They are the most precision rubber part that you can purchase. O-rings are manufactured to a tolerance of ± 0.003 inches (0.08 mm)

You can buy them anywhere. There are plenty of distributors. Unlike other shapes, most designers have settled on only a few O-ring cross

sections, making spare parts and inventory a lot easier. Their cost is low compared to other shapes. Because they are self-energizing there is no need to spring-load them to the

shaft or sleeve. This means that the seal spring or springs can be designed for face loading only.

You cannot put them in backwards.

In recent years the elastomer industry has produced a variety of newer compounds that appear to be getting closer to the universal rubber that we are all seeking. Unfortunately we are not there yet, so this article is an attempt to put these "super compounds" into a proper perspective. There are several of these compounds that you should know about.

KALREZ®, a Dupont product that is not a true elastomer so you will experience some compression set depending upon the compound you select. You have a few choices of compounds:

Compound 4079, A "low compression set" compound (about 25% compression at 400°F) (205°C). Can be used to 600°F (316°C) Not recommended for hot water or steam applications, or in contact with certain hot aliphatic amines, ethylene oxide and propylene oxide.

Compound 1050, Slightly harder than 4079. Can be used to 500°F (260°C) in non-oxidizing environments. Not recommended for pure water or steam at higher temperatures. This compound is scheduled to be phased out of production.

Compound 2035, To 425°F (218°C) It is the compound recommended for Ethylene Oxide and Propylene Oxide service. It also exhibits low swell in organic and inorganic acids, esters, ketones, and aldehydes.

Compound 1018, To 550°F (288°C). It has better hot water/ steam resistance than all other compounds except 3018. Not recommended for use in organic or inorganic acids at high temperature or for rapid temperature cycling applications.

Compound 3018, To 600°F (315°C). It has the best hot water/steam resistance and the best high-pressure extrusion resistance. It is too hard for most mechanical seal applications at temperatures below 400°F (205°C).

The following compounds are exhibited on the special elastomers chart

CHEMRAZ is distributed by Greene, Tweed & Company, telephone (714) 875 3301. It is similar to KALREZ and can be used to 400°F (205°C). It is available in both black and white O-rings.

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FLUORAZ - is another product distributed by Greene Tweed & Company, telephone (714) 875 3301. It can be used to 400°F (205°C). Field experience indicates that in operation it appears t o be very similar to AFLAS.

AFLAS is distributed through the 3M company, telephone (612) 733 5353. It can be used to 400°F (205°C)

To be classified as a true elastomer you should be able to compress the O-ring and have it return to 90% of its original shape in less than five seconds after the compression force is removed. It is this elasticity that gives the compound its memory and eliminates the need for spring loading the elastomer to the seal shaft or sleeve. If the compound does not return to 90% of its original shape in five seconds or less it is called a plastic and becomes less desirable as a dynamic seal in mechanical seal design. Many of these "super compounds" are plastics and present sealing problems in some seal configurations. You are going to have to depend upon your experience to select individual seal designs that work well with these materials.

Some distributors of these compounds recommend the use of mechanical seals with spring loaded dynamic O-rings. They do this to booster their sales of the compound. They forget to mention that when you spring load one of these compounds you will experience shaft fretting under the O-ring. This shaft fretting increases the probability of seal failure, and dictates the use of shaft sleeves that raise the L3/D4 rating of the shaft, contributing to excessive shaft deflection.

There are many charts available to help you pick the correct elastomer compound for your application. Unfortunately your fluid may not be shown on some of these charts and the temptation is to go to one of the special elastomers for the solution. At other times you will tempted to standardize on a special elastomers to avoid the selection process altogether. The next chart should help you to avoid a mistake in both of these instances.

The special elastomers chart is unique in that it shows you where these "super compounds" should not be used. This does not imply that if the chemical is not listed, or if no notation is made, that the compound is suitable for your service. It means nothing more than what it says; these are the chemicals that each manufacturer has designated as not suitable for a dynamic O-ring application.

A = Aflas C = Chemraz C* = White colored Chemraz F = Fluoraz K = Kalrez® n = According to the manufacturer this compound is not suitable for either

dynamic or static mechanical seal O-ring service. In some cases a compound was given an "n" rating when field experience proved that the published compatibility information was incorrect.

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c = Caution. May be suitable for static service, but probably not for a dynamic application. The higher the fluid operating temperature the less acceptable. You may want to check for experience in your plant or test the O-ring in your fluid to be sure.

If there is any question about the use of one of these compounds in a given service you can test the compound by immersing the O-ring in the fluid to be tested for about ten days to two weeks. If the fluid is going to attack the compound, the O-ring it will change weight, shape, or appearance. If the application is going to be at a hot temperature, you might want to put the test container in an oven to duplicate the seal operating conditions.

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CHAPTER 5

THE ENVIRONMENTAL CONTROLS 5.1 Seal Application problems

For any given seal application problem there are three generally accepted solutions:

Put in a standard or "off the shelf" seal and hope it works. Build a special seal that can compensate for the problem once it

occurs. Control the environment surrounding the seal to prevent the problem

from occurring in the first place. If you control the seal environment you will avoid the inventory and delivery problems associated with special seals.

In the following paragraphs I will:

Address the subject of environmental controls in detail. Show you how to seal each of the categories. Show you how to seal the special operating conditions. Discuss some special seals

It turns out there are only a few things you can do in the stuffing box area to control the environment around the mechanical seal. As an example you can:

Control the temperature in and around the stuffing box. You can raise the temperature, lower it or keep it within certain limits

You can control the pressure in the stuffing box. You might want to raise it to prevent a product from vaporizing or you might want to lower it to save the expense of going to a high pressure seal.

You can control the pressure between dual seals. There are occasions when you will have to raise this pressure, lower it or keep it within narrow limits.

You can replace the fluid in the stuffing box. The replacement fluid may be less dangerous, a good lubricant or just easier to seal.

You can keep atmosphere away from the outside of the seal because the moisture in atmosphere can cause problems with some seal applications.

Here are some ways to control the temperature in the stuffing box area.

Flush the stuffing box with a compatible cool clean liquid. Many seal glands have this connection available in a more convenient location than the stuffing box lantern ring connection.

Flush is a misunderstood term. It describes six very different functions. Please look at the following illustrations and note the connections.

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Discharge recirculation. In this arrangement a line is connected from the discharge side of the pump to the lantern ring connection in the stuffing box (A) or an appropriate connection in the gland.

The fluid flows from the discharge side of the pump through the stuffing box to the back of the impeller.

 

Suction recirculation. This time the recirculation line is connected from the bottom of the stuffing box to the suction side of the pump or some other low pressure point in the system.

It uses the same connection (A) but on the bottom side of the stuffing box. The bushing in the bottom of the stuffing box must be locked into place with a snap ring or it could move with the differential pressure.

Jacketing fluid. The cooling or heating fluid flows through a jacket (B) that is surrounding the stuffing box.

Be sure to go in the bottom and out the top of the jacket to prevent an air pocket

 

Barrier or buffer fluid. The fluid is circulated between two seals (E) either by convection, a seal pumping ring, or by a separate circulation system.

If the circulating fluid is at a higher pressure than the stuffing box it is called barrier fluid. If it is at a lower pressure it is called buffer fluid.

 

Quench. Please look at connection (D). The fluid (usually low-pressure steam) is passed between the seal and a disaster bushing that has been installed in the rear of the seal gland.

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This is also called an API (American Petroleum Institute) gland

Flush. Please look at connection (C). A liquid, from an outside source is injected into the stuffing box at one atmosphere above stuffing box pressure and dilutes the product you are pumping.

Use two seals with a cool liquid circulating between them. A two way balanced cartridge seal would be an excellent choice. This arrangement provides cooling at the seal faces where it will often do the most good.

Use the jacketed stuffing box that came installed on the pump (connection "B") or install one if it is missing. These jackets are available as a replacement part for the back plate on most popular pumps or as an after market bolt on accessory. To use the jacket properly:

o Dead end the fluid you are trying to control. This means no lines in or out of the stuffing box except those used to circulate the jacketing fluid.

o Install a thermal bushing in the bottom of the stuffing box. Carbon is a good choice because it is a poor conductor of heat compared to the metal pump components. A typical clearance over the shaft would be 0.002 inches per inch of shaft diameter (0,01 mm/mm of shaft diameter).

o Circulate the heating or cooling fluid through the jacket to control the temperature. Six to eight gpm. (25 to 30 liters /min.) is typical of the amount of cool water needed to cool down heat transfer fluid to the point where it will stop "coking" and viton O-rings will be acceptable. If your water is too hard you should substitute condensate or low pressure steam.

An API (American Petroleum Institute) gland is available for most mechanical seals (connections C & D). The gland has several features to provide various functions. It can be used as:

o A quench connection (D) to provide heating or cooling outboard of the seal or to remove any liquid or vapors that might escape between the seal faces. Steam can be injected to lower the seal temperature in the event of a fire. In the event of a major seal failure this quench connection can be used in conjunction with the gland disaster bushing to direct seal fluid leakage to point where it can be collected. Be careful of using too much steam pressure because the steam will leak through the disaster bushing and blow through the lip seal trying to protect the bearings.

o A flush connection (C) to provide clean fluid to the stuffing box, or it can be used to vent air out of the stuffing box in a vertical pump application.

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o A close fitting, non sparking disaster bushing to provide shaft support in the event of a bearing failure or to protect personnel in the event of a massive seal failure. The bushing will direct most of the leakage to a drain or tank where it can be collected.

Heat tape or tracing lines can be installed around the stuffing box to provide a limited amount of temperature control.

Install a cooler in the line between the pump discharge and the stuffing box. Keep in mind that this system only works while the pump is operating so it would be of no value if the application problem occurs during pump shut down or when the pump is used in a "standby mode".

Use only balanced seals in these applications to avoid the heat problems associated with unbalanced seal designs. Elastomers positioned close to the lapped faces or the use of two hard faces should also be avoided for the same reason.

5.2 Controlling the pressure in the stuffing box area

Increase stuffing box pressure by installing a recirculation line from the pump discharge back to the stuffing box (connection A) with a close fitting bushing in the bottom of the stuffing box. Try to avoid positioning the recirculation line so that it aimed at the lapped seal faces or thin bellows seal plate materials. Many fluids contain solids that will abrade these parts. Be sure the close fitting bushing is positively retained in the bottom of the stuffing box. A snap ring is generally good enough to hold the bushing against the bottom of the suffing box.

Eliminate the pressure drop between seal faces by using two seals with a higher-pressure barrier fluid circulating between them. This is very important in the sealing of chemicals such as ethylene oxide that will penetrate into the dynamic elastomer, expand and blow out the other side causing severe damage to the elastomer and unwanted leakage.

Flush the stuffing box with a higher-pressure liquid. This is the best solution if the fluid contains solid particles that could interfere with the seal movement. If you are using balanced mechanical seals designed with the springs out of the fluid you will need only a small amount of flushing.

The only reason you would want to lower stuffing box pressure is because your seal does not have high pressure sealing capability. It is possible to lower stuffing box pressure by the use of environmental controls, but a high-pressure seal would be a much better choice. In an emergency you could lower the pressure by one of the following environmental controls:

Equalize the pressure in the stuffing boxes of a double ended pump by connecting the stuffing boxes together to get even seal wear. This is a common application for a double ended centrifugal pump.

It is possible to lower stuffing box pressure by installing a close fitting bushing in the bottom of the stuffing box and recirculate to the suction side of the pump. Be sure to "lock in" the position of this bushing with either a snap ring or some other retaining device to prevent it from moving towards the seal. Be careful of using this control on a vertical

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turbine pump because the high velocity liquid recirculating to the suction can heat up the line to the point where it can become "red hot".

Lower the sealing pressure differential on the inside seal of a dual seal application by utilizing an intermediate fluid pressure between two tandem seals. Be sure the inner seal is balanced in both directions." Balancing a seal in two directions is sometimes called "two way balance".

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CHAPTER 6

Troubleshooting mechanical seals

6.1 Reasons Of Seals failure

Dirt or solids penetrate the opened face.

Damage to seal components due to overheating and wrong use of a cleaner.

Seal failure could be analysed under following considerations-

Weather there is any evidence of corrosion. How is the wear patterns on the rubbing parts. Is there any evidence of rubbing or wear on those components that

should not be in contact. Change in colour of metal components. Evidence of missing parts such as Springs, set screws and drive lugs. Loose parts. Product on the rotating component.

6.2 Inspection of the individual components.

6.2.1 THE CARBON FACE

Chipping on the O.D. of the carbon. Indicate vibration.

This can be due to harmonic vibration, or critical speed of the rotating part.

Poor handling is a common cause. Liquid vapors causing the faces to rapidly open and close due to

cooling of face. Recirculation line is directed at the carbon seal face. The pump is cavitating. Water hammer.

Pits in the carbon face. This problem is usually due to inferior carbon/ graphite material.

Exploded carbon. Heating causes air bubles to explode out from the material and form pits. Prior to pitting polished patches will be visible, usually with small cracks visible in the center.

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If the liquid being pumped solidifies between the faces it will erode out pieces of the carbon at start up. This is a common occurrence with ammonia compressor seals because petroleum oil is mixed with the ammonia and it can coke at the elevated temperature.

Most petroleum products will "coke" because of the higher face temperature, and pull out small pieces of the carbon as the faces rotate. You will see evidence of these small pits if you inspect the carbon face under a magnifying glass.(HERE)

Chips at the I.D. of the carbon

Solids, or a foreign object of some type from outside of the pump are getting under the gland and are being thrown into the seal faces. This can occur if the seal leaked at some time and the product solidified on the outboard side of the seal. It can also occur if liquid, containing solids, is used in the quench connection of an A.P.I. type gland.

If the seal was installed outside of the stuffing box, as is the case with non metallic seals, solid particles in the fluid can be centrifuged into the rotating carbon face.

If the stationary face is manufactured from carbon it can be chipped if it comes into contact with the rotating shaft. This is a common problem at pump start up, or if the pump is operating off of its B.E.P.

Phonograph finish on the carbon face.

A solid product was blown across the seal face. This happens in boiler feed water applications.

Chemical attack of the carbon.

You are using the wrong carbon. Something in the product or the flush is attacking the carbon filler. Switch to an unfilled carbon such as Pure grade 658 RC or C.T.I. grade CNFJ.

You are trying to seal an oxidizing agent. Oxidizers attack all forms of carbon including the unfilled type. The carbon combines with the oxygen to form either carbon monoxide or carbon dioxide.

Some forms of de ionized water will pit and corrode carbon faces

Cracked or damaged carbon face.

The product is solidifying between the faces. Carbons are strong in compression but weak in tension or shear. This problem is common with intermittent pumps each time they start up.

Excessive vibration can bang the carbon against a metal drive lug. A cryogenic fluid is freezing a lubricant that was put on the face. The elastomer is swelling up under a carbon or hard face. The shaft is hitting the stationary face or the rotating seal face is hitting

a stationary object. Mishandling.

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Poor packaging. The lapped seal faces should be able to survive a 39" (one meter) drop.

Ice is forming on the outboard side of the seal and preventing the seal from moving to compensate for face wear.

A coating is forming on the carbon face:

A change in temperature. Many products solidify at temperature extremes.

The product is taking a pressure drop across the seal faces and solidifying.

Selective leaching is picking up an element from the system and depositing it on the seal face.

The stuffing box is running under a vacuum because the impeller was adjusted backwards and the impeller "pump out vanes" are causing the vacuum.

The system protective oxide is depositing at the faces. In hot water systems we experience this problem with magnetite (Fe3O4) until the system stabilizes.

Coking

This is a problem with all oils, and petroleum products in particular. Coking is caused by the combination of high temperature and time.

Contrary to popular belief the presence of air or oxygen is not necessary.

Shiny spots, cracks and raised portions of carbon.

The carbon is not dense enough, causing the expanding gases trapped beneath the surface of the carbon to explode through the face.

Product is solidifying between the faces and pulling out pieces of the carbon as the seal revolves.

Excessive carbon wear in a short period of time. Evidence of excessive heat is usually present.

Heat checking of the hard face. It shows up as a cracking of the hard face. This is a problem with coated or plated hard faces. Cobalt base tungsten carbide is a typical example.

The shaft is moving in an axial direction because of thrust. This can cause an over compression and heating of the seal faces

The impeller is being adjusted towards the back plate. This is problem with seals installed in Duriron pumps or any other pump that adjusts the open impeller against the back plate.

Any installation problem: The inner face of a "back to back" double seal application is not

positively locked in position. A snap ring must be installed to prevent the inboard stationary face from moving towards the rotating face when

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the high pressure barrier fluid pressure is lost or overcome by system pressure.

The seal was installed at the wrong dimension. A cartridge double seal was installed by pushing on the gland. Friction,

between the shaft and the sleeve O-Ring is compressing the inner seal.

A vertical pump was not vented. Solids have penetrated between the faces. The faces are not flat. The movable face is sluggish. The product is vaporizing between the faces because of either high

temperature or low stuffing box pressure . Non lubricants will cause rapid face wear. A non lubricant is any fluid with a

film thickness less than one micron at its load and operating temperature..

The carbon has a concave or convex wear pattern

High pressure distortion. The stationary face is not perpendicular to the shaft. Some companies lap a concave pattern as standard. Check with your

manufacturer. The shaft is bending because the pump is running off of its B.E.P.

The carbon is not flat.

Mishandling. Poor packaging. The hard face has been installed backwards and you are running on a

non lapped surface. The seal was shipped out of flat. The metal/ carbon composite has not been stress relieved and it is

distorting the carbon. When the carbon was lapped the lapping plate was too hot and as a

result, not flat. The carbon was lapped at room temperature and the seal is running at

cryogenic temperatures. Solids are imbedded in the carbon. The faces have opened.

o The seal was set screwed to a hard shaft. o The elastomer (rubber part) is spring loaded to the shaft causing

the faces to open as the shaft moves due to end play, vibration or carbon wear. The shaft/ sleeve is over sized causing an excessive interference between the elastomer and the shaft/ sleeve.

o The sleeve finish is too rough. o The product has changed from a liquid to a solid. o Dirt or solids are interfering with the seal movement. o Some one put the wrong compression on the faces. o Shaft fretting is hanging up the face. o The face has been distorted for some reason allowing solid

particles to enter.

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o The sliding elastomer has swollen up causing too much interference on the shaft/ sleeve.

o Poor centering is causing the rotating face to run off the stationary face. Keep in mind the gland bolts are not always concentric with the shaft.

o The single spring was wound in the wrong direction. o An out of balance rotating assembly or bent shaft is causing the

rotating face to "run off" of the stationary face.

6.2.2 THE HARD FACE.

Chemical attack.

Some ceramics and silicone carbides are attacked by caustic. Check to see if your seal face contains silica. As an example: both reaction bonded silicone carbide and 85% ceramic have this high silica content.

Cracked or broken.

The product is solidifying between the faces. Most hard faces have poor tensile or shear strength.

Excessive vibration will cause cracking at the drive lug location.. A cryogenic fluid is freezing a lubricant that was put on the face. The elastomer is swelling up under an outside seal face. This problem

can also occur if the seal design allows a spring to contact the I.D. of the hard face.

The shaft is hitting the stationary face or the rotating seal face is hitting a stationary object.

Mishandling. Poor packaging.

Heat check (a common problem with coated or plated faces)

Caused by a high heat differential across the face. Most hard coating have only one third the expansion rate of the stainless steel base material.

Hard coating coming off of the face.

The base material not compatible with the sealed product. These coating are very porous so if the product attacks the base material the coating will come off in sheets.

The plating process was not applied correctly.

Analysis of the wear track on the hard face.

Deep grooves&emdash;excessive wear. Solids imbedded in the carbon are causing the problem. The solids were trapped between the faces when the seal faces opened.

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The seal was set screwed to a hard shaft. The elastomer is spring loaded to the shaft preventing it from flexing as

the shaft vibrates.. The shaft/ sleeve is over sized causing the dynamic elastomer or

bellows vibration damper to hang up.. The shaft/ sleeve finish is too rough The product has solidified in the seal components. Dirt or solids are interfering with seal movement. Not enough spring compression on the faces. Fretting of the shaft/ sleeve is hanging up the face. The face has been distorted by either excessive temperature or

pressure. The sliding elastomer has swollen up due to chemical attack of the

product or a cleaner that was flushed through the lines. The wrong choice of rubber lubricant, at installation, can also cause the problem

Poor centering is causing the rotating face to run off of the stationary face..

The single spring was wound in the wrong direction.

The wear track is wider than the carbon.

Worn bearings. Bent shaft. Unbalanced impeller. Sleeve not concentric with the shaft. Seal not concentric with the sleeve. In a stationary seal, the stationary carbon is often not centered to the

shaft, causing a wiping action.

The wear track is narrower than the carbon.

The soft face (carbon) was distorted by pressure. The hard face was over tightened against an uneven surface. The hard face clamping forces are not "equal and opposite". The face never was flat, or it was damaged during shipment.

Non Concentric pattern. The wear track is not in the center of the hard face.

The shaft is bending because the pump is running off of its best efficiency point.

Poor bearing fit. Pipe strain. Temperature growth is distorting the stuffing box. The stationary face is not centered to the shaft. Misalignment between the pump[ and its driver.

Uneven face wear. The hard face is distorted:

High pressure. Excessive temperature.

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Over tightening of the stationary face against the stuffing box. The clamping forces are not equal and opposite. The hard face is not wide enough. You are using a two bolt gland and the gland is too thin causing it to

distort. You are using a pump seal in a motion seal application.

The product is sticking to the seal face. The product is changing state and becoming a solid. Most products solidify for the following reasons:

A change in temperature. A change in pressure. Dilatants will solidify with agitation. As an example: cream becomes

butter. Some products solidify when two or more chemicals are mixed

together.

The hard face is not flat.

Mishandling. Poor packaging. The hard face has been installed backwards and you are running on a

non lapped surface. It was shipped out of flat.

6.2.3 THE ELASTOMER.

Compression set. The O-ring has changed shape.

… High heat is almost always the cause unless you are dealing with Kalrez, Chemraz, or a similar material where a certain amount of compression set is normal.

Shrinking, hardening or cracking.

High heat. The shelf life was exceeded. This is a big problem with "Buna N" that

has a shelf life of only twelve months. Cryogenics will freeze just about any elastomer. Chemical attack normally causes swelling, but in rare cases can

harden an elastomer. Oxidizing liquids can attack the carbon that is used to color most

elastomers black.

Torn nibbled, or extruded.

Mishandling. Sliding over a rough surface. Forced out of the O-Ring groove by high pressure.

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The liquid has penetrated the elastomer, vaporizing inside and blowing out pieces. This is a problem with Ethylene Oxide.

Halogenated fluids can penetrate the Teflon coating on an elastomer and cause the base material to swell up, splitting the Teflon jacket.

Swelling, changing color, weight or size. Almost always caused by:

Chemical attack. Be careful of the lubricant used to install the elastomer. Solvents or cleaners used in the system may not be compatible with

the elastomer. Some compounds are sensitive to steam. Most Vitons are a good

example of this problem. The elastomer is not compatible with something in the fluid you are

sealing.

Torn rubber bellows.

The bellows did not vulcanize to the shaft because you used the wrong lubricant.

The shelf life was exceeded. The seal faces stuck together and the shaft spun inside the bellows. The pump discharge recirculation line was aimed at the rubber bellows.

Solids entrained in the high velocity liquid are abrading the bellows.

6.2.4 THE METAL CASE OR BODY OF THE SEAL.

Corrosion.

General or overall. This is the easiest to see and predict. The metal has a "sponge like" appearance. It always increases with temperature.

Concentrated cell or crevice corrosion. Caused by a difference in concentration of ions, or oxygen in stagnant areas causing an electric current to flow. Common around gaskets, set screws, threads, and small crevices.

Pitting corrosion. Found in other than stagnant areas. Extremely localized. Chlorides are a common cause. Can be recognized by pits and holes in the metal.

Stress corrosion cracking. Threshold values are not known. A combination of chloride, tensile stress, and heat are necessary. Chloride stress corrosion is a serious problem with the 300 series of stainless steels used in industry. This is the reason you should never use stainless steel springs or stainless metal bellows in mechanical seals.

Inter granular corrosion. Forms at the grain boundaries. Occurs in stainless steel at 800-1600 F. (412-825 C.), unless it has been stress relieved. A common problem with welded pieces. Stabilizers such as columbium are added to the stainless steel to prevent this. Rapid cooling of the welds, the use of 316L and stress relieving after the welding are the common solutions.

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Galvanic corrosion. Occurs with dissimilar materials in contact with and connected by an electrical current. Common in brine, caustic, and salt water applications.

Erosion / Corrosion. An accelerated attack caused by a combination of corrosion and mechanical wear. Vaporization, liquid turbulence, vane passing syndrome, and suction recirculation are special cases often called cavitation. Solids in the liquid and high velocity increase the problem.

Selective leaching. Involves the removal of one or more elements from an alloy. Common with demineralized or de ionized water applications.

Micro organisms, that will attack the carbon in active stainless steel.

Rubbing--All around the metal body.

A gasket or fitting is protruding into the stuffing box and rubbing against the seal.

The pump discharge recirculation line is aimed at the seal body. The shaft is bending due to the pump operating off of its best efficiency

point. Pipe strain. Misalignment between the pump and its driver. A bolted on stuffing box has slipped.

Partial rubbing -- On the metal body.

Bent shaft. An unbalanced impeller or rotating assembly. Excessively worn or damaged by corrosion or solids in the product. The product has attached its self to the impeller. The impeller never was balanced. The impeller was trimmed, and not re balanced. The seal is not concentric with the shaft, and is hitting the stuffing box

I.D..

 

Discoloration. Caused by high heat. Stainless steel changes color at various temperatures.

FAHRENHEIT COLOR OF THE METAL CENTIGRADE

700 - 800 Straw Yellow 370 - 425

900 - 1000 Brown 480 - 540

1100 - 1200 Blue 600 -650

> 1200 Black > 650

NOTE: To tell the difference between discoloration caused high heat and product attaching to the metal part, try to erase the color with a common pencil eraser. Discoloration will not erase off.

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Product sticking to the metal surfaces.

Heat is the main cause. The product pressure has dropped. Air or oxygen is getting into the system. Valves above the water line. Through the stuffing box. The product was not deaerated. The pump suction is not completely submerged. The bypass return is too close to the pump suction. The liquid is vortexing in the suction line. A non O-Ring elastomer is being used in the seal allowing air to enter

the stuffing box when you are sealing a vacuum application. The system protective oxide coating is depositing on the sliding metal

components.

The following applications cause a vacuum to be present in the pump stuffing box.

Pumps that lift liquid. Heater drain pumps. Pumping from an evaporator. Pumping from the hot well of a condenser. Pumps that prime other pumps. The open impeller was adjusted in the wrong direction and the impeller

pump out vanes are causing the vacuum.

The Teflon coating is coming off some of the metal parts.

Coatings are very porous. They do not provide corrosion resistance. The base material is being attacked by the product.

DRIVE LUGS, PINS, SLOTS, etc.

Broken.

Chemical attack. Excessive side load. The seal faces are glued together because the product has solidified. A cryogenic fluid is sticking the faces together.

Wear on one side of the drive lug or slot.

Vibration. Slipstick. The stationary is not perpendicular to the shaft.

The drive pins are falling out of the holder.

Corrosion.

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Improper fit. Bad part. Excessive vibration.

6.2.5 THE SPRINGS.

Broken or cracked.

The stationary face is not perpendicular to the shaft causing excessive spring flexing in the metal "plastic range". The spring material has "work hardened" and fatigued.

Chloride stress corrosion problems with 300 series stainless steel.

Corroded.

Stressed material corrodes much faster than unstressed material. The springs are always under severe stress.

Clogged.

Be sure to distinguish between "cause and effect". If the springs are located outside the liquid, it happened after the failure.

If the product solidifies or crystallizes it can clog springs exposed to the pumped fluid.

Dirt or solids in the fluid can clog exposed springs.

Twisted.

Almost always an assembly problem. The lugs were not engaged in the slots. This is a problem with many seal designs. Check to see if your seals can come apart easily or if the drive lugs can change position when the seal is not compressed.

The drive lugs or slots are worn on both sides.

Excessive vibration. The single spring, rubber bellows seal, was not vulcanized to the shaft. The stationary is not perpendicular to the shaft, causing excessive

spring movement.

Broken Metal Bellows.

Fatigue caused by over flexing in the plastic range of the metal o Harmonic vibration. o Slipstick.

The discharge recirculation line is aimed at the thin bellows plates. Excessive wear from solids in the stuffing box. Faces sticking together as the product solidifies. Chloride stress corrosion with 300 series stainless steel.

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Because these seals do not have a dynamic elastomer to provide vibration damping some other means must be provided or vibration will always be a problem.

6.2.6 THE SLEEVE, OR SHAFT.

Grooves or pits at the seal dynamic elastomer location.

Fretting. Concentrated cell corrosion. The rubber bellows did not vulcanize to the shaft/ sleeve. The set screws slipped on a hardened shaft or were not tightened

properly. The seal faces stuck together causing the shaft to rotate inside the static elastomer.

Salt water applications are particularly troublesome when a static elastomer or clamp is attached to the shaft. Pitting caused by the chlorides and the low PH of salt water are the main problems.

Rubbing at the wear ring location.

The pump is running off of its best efficiency point. The shaft is bending. Bad bearings. Excessive temperature. Sleeve is not concentric with the shaft, or the seal with the sleeve. Bent shaft. Unbalanced impeller or rotating assembly. Pipe strain. Misalignment between the pump and its driver High temperature applications require a "center line: pump design.

Corrosion. See above description under metal corrosion

6.2.7 THE SET SCREWS.

Stripped from over tightening. Corroded. Check to see if you are using hardened set screws. This

type is normally supplied with most cartridge seals and can corrode easily.

Rounded Allen Head. Alan wrenches wear rapidly. They are an expendable tool.

Loose. o Sleeve too hard. They are not biting in. o Sleeve too soft. They are vibrating loose.

6.2.8 THE GLAND.

Rubbing at the I.D.

Partial rubbing.

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The gland has slipped. Improper installation. It was not centered to the shaft. The shaft is bending. Pipe strain. Rubbing all around. The shaft is not concentric with the sleeve. The seal is not concentric with the sleeve. Bad bearings. Bent shaft. Unbalanced impeller or rotating assembly. Solids attached to the shaft, or caught between the shaft, and the

gland. Cavitation.

Corrosion.

If there is evidence of rubbing the corrosion will be accelerated.

Passages clogged or not connected properly.

A.P.I Gland. o Hooked up wrong. o Flushing connection clogged. o Quench connection clogged.

6.2.9 BUSHINGS

Rubbing at the I. D.

Partial rubbing. The A.P.I. gland has slipped. Improper installation. It was not centered to the shaft. The shaft is bending. The gland bolt holes are often not concentric with the shaft/ sleeve. Misalignment between the pump and its driver. Excessive pipe strain. Rubbing all around. The shaft is not concentric with the sleeve. The seal is not concentric with the sleeve. Bad bearings. Bent shaft. Unbalanced impeller. Cavitation

Erosion.

Dirt and solids are present in the discharge or suction recirculating fluid.

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