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The use of Duplex Stainless Steels (DSS) in refinery sour environments is governed by ANSI/NACE MR0103/ISO 17945NACE “Metallic materials resistant to sulfide stress cracking in corrosive petroleum refining environments” which limits DSS base materials to be used in Hydrogen Sulfide (H2S) services to a maximum hardness of 28 HRC for materials with a PREN ≤ 40 and to a maximum hardness of 32 HRC for those materials with PREN > 40.1 These hardness values are in line with the hardness requirements of solution annealed as produced straight tubes, but when the heat exchanger design requires the use of integral finning or u-bend tubes, these are subject to significant work hardening that results in as bent and as finned heat exchanger tubes with hardness measurement as high as 418 HV0.5 or 35.6 HRC which clearly exceeds the allowable limits stated above.
Strain calculations, pitting resistance, and chloride stress corrosion cracking testing are currently used as the key indicators to delimit the minimum bend radius for 22% chrome duplex stainless steels without heat treatment to be 3.3 times the tube diameter for u-bend heat exchanger tubing. However, existing data does not address the limitations of this alloy, in the as cold worked condition, for sour services in the refining industry. This study evaluates the sulfide stress corrosion cracking resistance of as-bent and integrally finned 22% Cr duplex stainless steel UNS-S32205 tubing for refinery sour services by presenting hardness data and corrosion testing per ASTM G48 and NACE TM0177 of tight u-bend specimens with bend radius up to 1.5 times the tube diameter as well as integrally finned tubes. As a follow up from a previous study, the corrosion resistance of as finned 25% Cr super duplex stainless steel will also be presented.
Deep well casing is an important part of oilfield production. In the long service life of well casing, corrosion can result in wall thinning and even perforation of the casing due to contacting with soil, water and other naturally occurring substances within the formation. The most economic and effective method to decrease corrosion of well casing is cathodic protection (CP). However, the vertical depth of casing is several kilometers, and CP current requirements of casing in different layers are quite different. At the same time, the conductivity of different formations will affect the distribution of CP current.
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Top of line corrosion (TLC) is a degradation mechanism predominantly encountered in the oil and gas industry. Initiation of TLC requires a stratified flow regime with wet gas transportation and the existence of a significant temperature gradient between the hot fluid inside the pipeline and the colder external environment.1,2,3 This temperature difference results in the condensation of water vapor, present in the gas phase, onto the cooler, upper internal section of the pipeline. The condensed water can be particularly aggressive as it lacks dissolved salts (e.g. bicarbonates), some of which are able to buffer the bulk electrolyte, increasing the pH and suppressing corrosivity.4,5,6 The absence of such salts typically results in a very low pH condensate (<pH 4), often containing dissolved acidic gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S), and also acetic acid (HAc), which can cause severe degradation, particularly in the form of localized corrosion.5