Best Practices in

Pilot Plant Piping

Richard Palluzi

April, 2013

2

The ideal piping for a pilot plant would be:

• Leak resistant

• Easily modified

• Able to accommodate varying requirements

• Easy to install

• Low cost

• Available in many different materials of construction

• Available in all sizes

• Have fittings available in numerous configurations

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Leak Resistance

• Pilot Plants are more subject to leakage than process plants

– Smaller size

– Larger number of joints

– Constant modifications

– Need to accommodate accessibility, flexibility and change

• Common types of piping used in pilot plants

– Piping

+ Threaded

+ Welded and flanged

+ Groved

– Tubing

+ Compression fittings

+ Vacuum fittings

+ Mechanically joined

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Best Practice: Tubing

• Available in numerous materials

• Fittings are readily available up to 1” OD

• Easier to install and modify

• Requires less skill, tools and training for

installation

• Smaller and lighter than pipe

• Lower cost than pipe

• Ability to bend

– Reduces need for fittings (lower cost and less

potential for leakage)

– Easier to install in tighter locations

– Allows for easier removal of components for

cleaning, modification or inspection

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Best Practice: Compression Fittings

• Better leak resistance than threaded fittings

• Requires few tools and less training

• More expensive than pipe fittings

– Significantly faster to install so labor savings usually make then cheaper overall

• Each fitting is a potential disassembly point

– Do require clearance although much less than piping

• Significantly better make/break life than pipe fittings

– But not infinite!

• Numerous specialty fittings available

• Many small valves and associated components available

• Most compression fittings have limitations on tubing hardness

– Confirm the tubing you ordered is within specification

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Best Practice: Compression Fittings

• Recognize that compression fittings larger than ¾” may require

mechanical assistance

• Compression fittings have both minimum and maximum wall

thicknesses

– Too thin and the tube may collapse without swaging

– Too thick and the tube will not deform enough to prevent blowout

• Drilled through compression fittings, used for dip tubes,

thermocouples and similar uses, lose significant pressure ratings

OD(inches) Typical Pressure

Derating

½ and less 25%

5/8-3/4 50%

7/8 - 1 75%

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Best Practice: Vacuum Fittings

• Significantly better leak performance than threaded fittings

– Usually requires some welding to avoid additional joints

• More expensive than compression and pipe fittings

• Each fitting is a potential disassembly point

• Zero clearance fittings

• Long term make/break life

• Gasket surface is more prone to damage

– Awareness can reduce frequency

• Decision to use O-ring style or metal gasket is usually based on

temperature and pressure

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Best Practice: Threaded Piping

• Make sure the die is sharp and in good condition or the threads are

likely to be rounded and more prone to leakage

• Make sure the threading is the right length

– Longer or shorter lengths will leak

• Use good quality fittings

– Particularly unions

• Avoid threaded connections in cyclic service

– Temperature

– Pressure

• Lightly coat unions with lubricating oil before each assembly

– The coating greatly helps it to seal in gas service

• Recognize that threads over 1” NPS are increasingly difficult to seal

– Particularly in gas service

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Best Practices: Flanged Pipe

• Use raised face flanges whenever possible as they require less force

to seal

• Avoid threaded flanges

– Adds another potential leak point

– Often makes bolt alignment difficult if retightened

• Tubing is usually a better approach for pipe sizes ½” and smaller

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Best Practice: Specialty Piping

• Understand when specialty piping may be a viable or more effective

option

• Grooved piping allows for fast and easy disassembly

– Lower pressure (1,000 psig is typical)

– CS or SS only

– High materials costs

– Some specialty equipment (grooving tool) required

– Sizes below 1” NPS very limited

• Sanitary fittings allow for ease of cleaning

– Available for piping or tubing

– 304 or 316 SS only

– Lower pressure (300 psig is typical)

– High materials costs

– Sizes below 1/2” NPS very limited

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Best Practice: Specialty Piping

• Flare compression fittings are excellent for thermal cycling but are

generally only available in CS and brass

– Good for refrigeration systems

• Longer ferrule designs and cone and collar type compression fittings

extend the range of compression fittings to 15,000 or 60,000 psig

respectively

– Much more expensive

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Best Practice: Mounting

• Use vacuum fittings where frequent removal or cleaning is required

– Zero clearance makes layout easier

– Ability to replace gaskets maximizes service life

• Mount the valves not the tubing wherever possible

– Minimizes the stress on the fittings created when operating the valves

– Will reduce long term leakage

• Avoid unsupported elements

– Long spans

– Heavier components

– Flimsy supports

– All lead to increased leakage

• Use bends to allow for thermal expansion

– Even small temperature swings promote leaks over time

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Best Practice: Reduce Joints

• Fewer joints always mean fewer potential leak points

• Use specialty fittings to minimize joints

– Long term savings outweigh costs over time

– Requires some planning or stocking

• Weld joints that are:

– In difficult to reach locations

– Not likely to need to be opened

– Are on systems subject to routine or frequent temperature swings

– Under insulation

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Best Practice: Remember Maintenance

• Almost everything eventually needs maintenance

• Make sure easy removal is provided for:

– Instruments

– Rotating equipment

– Filters and strainers that need to be removed to be changed

– Reactors

– Regulators

– Relief devices

– Control valves

• Decide if you have clearance or need zero clearance fittings

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Best Practice: Leave Room

• Pilot plants are always modified

• Building a unit in too small a space:

– Adds to construction costs

– Makes future changes difficult or

impossible

– Greatly increases maintenance costs

• The Golden Rule: Plan on at least

twice the largest space you think

you’ll need

• Piping runs eat up space

• Insulation easts up space

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Best Practice: Training

• Train your operators and craft support regarding best piping

practices

• Always use a holdback whenever making or breaking any fitting

– Otherwise the fittings o neither side will start to leak

• Make up the fitting the proper amount

– Not too much, not too little

– Consider gauge blocks for compression fittings

• Never remove a support

• Make sure any changes or modifications are properly supported

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Best Practice: You Get What You Pay For

• Buy good quality pipe, tubing and fittings

• Use high quality gaskets and sealants

– Teflon tape and pastes generally work better than dopes

– Pastes require a minimum time for hardening

– Silver plated vacuum gaskets seal better than plain stainless

– Spiral re-enforced gaskets seal easier and last longer than flat gaskets

– Paying more for a good quality seal always ends up being more cost

effective!

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Best Practice: Heat Tracing

• Avoid joints wherever possible

• Use bends to accommodate thermal expansion

• Use standoffs to avoid having supports becoming heat sinks

• Use vacuum fittings when joints are necessary

• Mark insulation for joint location for ease of maintenance