External chloride stress corrosion cracking: Phenomenon and protection.

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Author: A. Anwer
Date: Aug. 2020
Publisher: Gulf Publishing Co.
Document Type: Article
Length: 1,217 words
Lexile Measure: 1340L

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After carbon steel, stainless steel remains the most commonly used material in the petrochemicals and oil and gas industries. Its long range of chemical resistance against corrosion has made it the first choice for owners/users. With an extended family of grades, stainless steel is resistant to many other damage mechanisms, as well. The variation of grades within austenitic stainless steel is appreciable, with each grade specified for special exposure. Significant runs of piping and equipment onsite made from stainless-steel material handle the most business-critical process service and serve as the lifeline to the least business-critical utility. Resistant to many damage mechanisms, stainless steel out in the open or under insulation is prone to a very delicate kind of stress corrosion cracking known as external chloride stress corrosion cracking (ECSCC).

ECSCC occurs in austenitic stainless-steel material in the presence of an aqueous chloride environment, tensile stress and temperature under insulation. When examining corrosion under insulation (CUI) for stainless-steel materials, ECSCC becomes more relevant. The cracking pattern of ECSCC is typically transgranular and highly branched with a spider-web appearance, as shown in FIG. 1. Factors leading to external stress corrosion cracking include type of stainless steel, presence of chlorides, stress temperature and insulating material. The greatest susceptibility to ECSCC is exhibited by austen-itic stainless steels with a nickel content of 8% (300 series: SS-304, SS-316, etc.). Greater resistance to ECSCC is generally shown by alloys of either lower or higher nickel contents. Moreover, duplex stainless steel is more resistant, and nickel-based alloys are highly resistant to ECSCC.

Origins and development. No definitive amount of chlorides presence triggers cracking, as the risk of their concentration always exists. Stress may be of an applied nature; however, the presence of residual stress may also initiate cracking. The critical temperature where cracking begins is typically 60[degrees]C (140[degrees]F), but cracking can...

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Source Citation   

Gale Document Number: GALE|A674970112