Process Piping Materials – Module 2 – M06-036

For lower diameter pipes (up to 6” in diameter), seamless pipes are recommended considering lower thickness in this range, which are detrimental in case of any weld deficiencies.

ERW/EFSW (Electric resistance welded/Electro-fusion seam welded) 8” to 14” pipes confirming to API 5L Gr. B are recommended for improved quality of ERW welding. For diameter 16” and above, EFSW pipes are recommended considering the superior welding quality. The recommended pipe specifications for Cooling Water and Fire Water services of different diameters are given below:

Up to 6”	Seamless Pipes Of A 106 Gr. B Or API 5L Gr. B
	Standards
8” to 14”	ERW/ EFSW pipes of API 5L Gr. B Standard
16” and above	EFSW pipes as per API 5L Gr. B Standard

3.9.Measures for Corrosion Protection

Corrosion is the destructive attack on a pipe by a chemical reaction with the materials and environment surrounding the pipe. The corrosion protection measures include:

wall thickness.

3.9.1. External Corrosion Protection

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Process Piping Materials – Module 2 – M06-036

epoxy plus a polyurethane topcoat. Heat resistant topcoats such as silicone acrylic or heat cure silicones are used for higher operating temperatures up to the melting point of zinc.

x Inorganic zinc coatings are NOT typically used under insulation, as zinc coatings exposed to water, at temperatures above 150°F (66°C) become passivated, which can result in the coating becoming a cathode to the steel, resulting in the preferential corrosion of the steel substrate. Where insulation is required, the inorganic zinc coating should be covered with an additional epoxy coating.

x Good practice is to procure bulk carbon steel piping with an inorganic zinc primer. The primer can then be top coated in the field with most high performance coating systems where the operating temperature is below the melting point of zinc 750°F (400°C). Insulated equipment and piping, where the process temperature is between 32°F (0°C) and 300°F (150°C), should be coated to provide protection against corrosion under insulation (CUI).

x When the temperature exceeds 300°F (150°C), no protection is required, as there is no corrosion due to absence of condensed water. Some owners have alternate temperature limits or require all surfaces to be coated regardless of temperature.

x Thermal Spay Aluminum (TSA) is an acceptable material for cyclic services with extreme temperature swings. TSA coatings are preferred by many clients; however, liquid applied coatings such as novolac and epoxy phenolic are also used at temperatures up to 400°F (200°C). When selecting a coating system for stainless steel, assurance that the coating will not promote stress corrosion cracking is a requirement.

x Galvanizing offers several constructability advantages such as minimal damage during handling and being a more forgiving work process.

x For cold insulation, when cellular glass with vapor stops, sealants, and vapor barrier are specified, the insulation system is inherently impervious to water, and will eliminate corrosion concerns. Other sealed insulation systems such as pre-insulated PIR systems with sealed vapor barriers offer the same degree of protection.

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