inspection and engineering unit 10.1

INSPECTION AND ENGINEERINGUNIT 10.1

SPECIALIST COATINGS

Objective:The objective of this training unit is to give an overview of some of the specialist coatings usedfor corrosion.

These specialist coatings are used throughout the globe in various locations includinghazardous environments, confined locations, pipelines, tank and vessel linings and areas oflimited access.

Technology:

Some specialist coatings have been available for a number of years to relatively small, but nichemarkets. New technology is also being pursued by both small and large coating suppliers wheretraditional paint and coatings have not worked or performed satisfactorily.

Testing evidence is essential for new products, however, track record and case studies will give theend user or specifier the confidence to apply the specialist coating to a particular level of surfacepreparations in a given environment.

All coatings will have a designed life and it is up to the specifier to ensure a thorough risk analysis isconducted on the asset being protected.

Copyright 2010 Fitz-Coatings Ltd


Coatings or Linings - Definition

Coatings

Usually defined as a material applied to the external of a structure and not necessarily subject toimmersion in a liquid or chemical.

The coating should prevent corrosion or disintegration of the structure by the environment.

Linings

Usually defined as a material applied to the interior of a structure and subject to immersion in liquidsor products.

The lining must prevent corrosion of the structure while preventing contamination of the containedproduct.

Specialist Coatings:



Some suppliers have specialist coatings in the true sense.

An example of the above is coatings that can be applied underwater or coatings that can be appliedto water splashed locations where it may be impossible or impractical to remove the water.

Typically, these coatings are based on epoxy resins with special additives. The coating is literallypushed onto the substrate where it will adhere and are either immersed, semi-immersed or exposedto the environment.

These products are generally solvent free and applied in thicknesses up to 1mm mixing andapplication must be in strict accordance with product data sheets.

Glass Flake:

The use of glass flake pigments has been available for a number of years in selective coatings. Theuse of large glass flakes in high build linings has found great success in tank and vessel linings.

The glass reinforces the coatings and reduces moisture, liquids etc. penetrating the linings andattacking the substrate.

These coatings offer excellent erosion properties and give long life performance.



Polyesters and Vinyl Esters:

Polyesters and vinyl esters have been used extensively since the early 1960’s due to their highchemical resistance.

These products are predominantly used as lining to both steel and concrete and can be available introwel or spray application. The trowel versions can be very thick (2-6mm) and may incorporatefibreglass cloth or matting systems between coats.

The full coating may also incorporate primers, intermediate coats, base coats or topcoats/gel coats.

The chosen system will depend upon the environment being protected.

Spray applied versions are used with typical thicknesses of 500 microns to 2-3mm.

It is important to assess the environment for using polyesters and vinyl esters:

• Temperature



• Liquid/contents

• pH value

• Special conditions such as pressures etc.

Other things to consider are the expected life of the system, cost, maintenance requirements andspecialist application procedures or equipment.

There is no doubt correctly specified and applied polyesters and vinyl esters will give long life, moreso with the vinyl ester which has superior chemical resistance.

Due to the generally high thickness of polyesters and vinyl esters, abrasive blast cleaning isessential.

A high quality surface preparation and surface profile is required.

The coatings should be applied strictly in accordance with the coating suppliers recommendations.

Full quality control will be required including:

• Surface preparation

• Environmental conditions

• Thickness

• Cure (including post cure)

• Holiday detection



Polyesters and Vinyl Esters:

This group of coatings are based on thermosetting resins and dissolved in an unsaturated monomer(typically styrene).

By adding a peroxide catalyst, a free radical additional reaction occurs that transforms the liquidresin into a solid film.

The peroxide catalyst will give the mixed product a short pot-life and specialist applicationequipment may be necessary.

Evaporation does not occur as the monomer is incorporated into the film.

Glass Flake Epoxy Coating:

Glass flake can also be incorporated into an epoxy resin.

The glass flake can be used in conjunction with anti-corrosive pigments such as zinc phosphate.



The use of glass makes the epoxy coating tough and durable and is used in harsh environmentssuch as offshore platforms, bridges, pipelines etc.

The glass flake coating is typically 250 to 500 microns and it is important that the glass size is nottoo big otherwise it may stand up and act like a wick.

The glass loading also varies between suppliers.

Rubber Linings:

Rubber linings are used extensively for protection of the interior of tanks and vessels also pipeworkand clamps in the splash zone of offshore platforms.

Natural and synthetic rubber linings are used in numerous industries including chemical, paper,mining, power etc. The physical properties of these rubber allows them to protect steel fromerosion, corrosion, abrasion and chemical attack.

Various grades of rubber are available, some remaining relatively soft while others are very hardand more wear resistant.

Different thicknesses of the rubber are used to suit the specification.



Rubber Linings:

The coating takes place in shops where the steel structure is abrasive blast cleaned.

A tie coat primer, which acts as a glue is applied to the blast cleaned substrate.

This primer must be applied in strict accordance with the suppliers data sheets regardingenvironmental conditions, thickness, cure etc.

The rubber lining is then applied by skilled applicators who use sheets of the rubber carefullyattached to the surface.

Special rollers are used to remove air etc.

Rubber Lining:

The rubber is then cured or vulcanised under pressure and hot air at approximately 130 °c to 140°cin a purpose built autoclave or oven.



The vulcanisation time varies depending upon the rubber etc, however, it is in the order of one hour.

Once cured the rubber must be thoroughly inspected:

• Visual – Imperfections, blisters, poor adhesion, inadequate overlap etc.

• Holiday detection – Full holiday detection using high voltage equipment. (This can also beconducted pre-cure).

• Hardness – As per specification.

• Adhesion – Test plates.

Tar and Asphalt Coatings:

Coal tar enamel and asphalt coatings have been used for over 80 years for pipeline protection.

The coal tar is derived from the coal carbonisation process while the asphalt, often referred to asbitumen is derived from the deposit remaining after the distillation of crude petroleum. Due to healthconcerns, the materials, especially the coal tar enamel, have been replaced by new moderncoatings. Notwithstanding the above coal tar enamel and asphalt coatings are still used in someparts of the world.



The coating of pipes takes place in shops.

The pipes are abrasive blast cleaned and primed, heated with the liquid tar poured over them.

The coating is applied in several layers reinforced with fibreglass layers. Typical thickness is3-6mm.

The surface temperature is 60-80°c.

Asphalt coatings have good water resistance and good resistance to cathodic disbonding and areused to an increasing extent over tar coatings.

The coating is hot poured with fibreglass at a thickness of 5-6mm.

Concrete coatings can be over applied for sub-sea environments.

Waxes and Greases:

A number of materials based on waxes, oils and greases are used for temporary protection of steel



components or for protection of steelwork, particularly in inaccessible areas.

Waxes and greases, sometimes containing inhibitors, are generally applied as thick, reasonably softfilms to provide barrier protection.

Some of the compositions are hot applied and are useful for injection into spaces.

Others are cold applied to produce an either hard wax-like or soft grease coatings.

Anti-Corrosive Tapes:

Anti-corrosive tapes are used for pipes and inaccessible areas such as valves, joints etc.

Plastic tapes and petrolatum or petroleum wax impregnated tapes have been used for numerousyears.

Thermoplastic tapes are applied both in the shop and in the field whereas petrolatum or wax tapesare most frequently applied at the site.

Surface preparation for new structures usually consists of abrasive blast cleaning prior to priming.

Existing structures such as pipes on petrochemical sites etc will generally be wire brushed andprimed.



Anti-Corrosive Tapes:

The tape must be applied in accordance with the suppliers application data sheets andrecommendations.

Tape machines are available for applying certain tapes while other tapes are applied manually.

The overlap must be consistent and the finished product must be free from twists, blisters, airpockets etc.

Holiday detection must be conducted once the tape has been applied.

The voltage should be in accordance with specific standards or the tape suppliersrecommendations.



Tank Coating and Lining:

You will recall that linings are used to prevent corrosion of the structure while preventingcontamination of the contained product.

Tank lining is a massive business as numerous products are stored, either to be used directly suchas fuel tanks or indirectly such as transport vehicles and ships.

All will have one thing in common, a high quality resistance and compliant coating will be required.

It is essential that the coating supplier is contacted during the review or design of a coating or liningfor a tank.

The supplier will have assessed the coating performance in the product and can advise onsuitability etc.

Specific testing is often conducted also which may be to a specific standard and is usuallyperformed independently from the supplier.



Ensure the certification and documentation is correct before specifying a product.

Tank Coatings

For tanks on chemical and product tankers, coatings have to be resistant to the cyclic conditions ofcarriage of a wide range of aggressive chemicals and tank cleaning.

The most frequently used tank coatings are pure epoxy, epoxy phenolic and zinc silicate.

Pure epoxy is generally used on product tankers that trade in clean petroleum products such asnaphtha.

Epoxy phenolics have a greater resistance to a wider range of aggressive cargoes such asethylene dichloride.

Zinc silicates find their used on chemical tankers when cargoes such as methanol or ethanol areregularly carried but are restricted to a cargo pH range of approximately 4 to 9.

Tank Coating and Lining:



Full inspection and quality control must be conducted on surface preparation, coating application,cure and testing.

The coating supplier should have full application data and procedures.

It is not uncommon to obtain insurance policies for such linings.

Holiday detection (low or high voltage) should also be conducted on the cured lining.

Some products require high temperature to cure such as special baked phenolics.

Powder Coatings:

Powder coating films are obtained when finely pulverised plastic compositions are applied to a metalor other surface and fused together by heat.

The two distinctive types are:

• Thermoplastic

• Thermosetting

Thermoplastics are high molecular weight products that melt, flow and form a film without a changein their chemical composition.

Examples include:

• Polyethylene

• Polypropylene

• Nylon

• Polyvinyl Chloride



Powder Coatings:

Thermosetting powders are low molecular weight polymers that cross-link during heat curing to formhigher molecular weight products.

Examples include:

• Epoxy

• Acrylic

• Polyurethanes

• Hybrids

The epoxy coating is, by far, the most common type of powder used for corrosion protection.

One particular type of epoxy used is the fusion bonded epoxy coating commonly referred to as FBE.

Powder coatings have a number of advantages and disadvantages.



Advantages:

• Tough durable coatings available in various types

• No VOC’s with minimum waste

• Available in a variety of properties and film thicknesses

• Ready to used (powder)

Disadvantages:

• Generally factory application

• Post curing required

The products can be used for protection of appliances, furniture, vehicles etc. as well as steelprotection such as pipelines.

Fusion bonded epoxy coatings are often applied to steel pipework for corrosion protection.

In some instances, specialist coatings are applied onto the powder coating.

For pipeline coatings, the powder is generally electrostatically sprayed onto a preheated pipe. Oncontacting the hot surface, the powder melts, flows, gels and within 2-3 minutes becomes a toughenamel coating.

Typical thickness is 350-450microns.

Thousands of miles of pipeline are now coated with fusion bonded epoxy around the globe.



Specialist Coatings:

There are other specialist coatings available to meet the criteria of specific location and applications.

Some products are formulated for corroded locations where abrasive blast cleaning is impossible.

Other coatings are formulated to go onto wet or damp surfaces.

It is important that the specifier or user is fully aware of the product use and requirements.

The coating supplier will give the necessary recommendations on surface treatment and application.

Plastic Coatings

Plastic coatings have been used in the industry for over fifty years, however this is generallyrestricted to specialist areas such as consumer markets and used for corrosion and impactresistance, electrical insulation and decorative finishes.

Coatings are applied by electrostatic (powder), dip (thermosetting) and thermoplastic spraying.



The coatings have found extensive use in the automobile market used on engine parts and variousparts of the car including grills, latches, springs, coils etc.

Coating examples include: polypropylene, polyethylene and polystyrene.


inspection and engineering unit 10.1

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