Evaluation Of Girth-Welded 22Cr Duplex Stainless-Steel Piping For Susceptibility To Environmentally Assisted Cracking (EAC), Pitting, And General Corrosion In A Sour Environment

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Product Number: 51321-16725-SG

Author: Jing Ning; Peter F. Ellis; Ramesh Rao; Brent Sherar

Publication Date: 2021

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The results of a stress corrosion cracking (SCC) qualification study of twenty-four heats of girth-welded 22Cr duplex stainless steel (DSS) piping are reported. This study evaluated the performance of either triplicate welded ANSI/NACE TM0177-2016 Method A tensile specimens or triplicate welded NACE TM0316-2016-compliant four-point-bend-beam (FPBB) specimens per heat exposed to a sour environment at 90 °C. All environmentally assisted cracking (EAC) specimens were stressed to an equivalent of 90% of their respective 0.2%-offset yield strengths at 90 °C to assess SCC susceptibility. In addition, duplicate welded corrosion coupons were machined per heat for determination of pitting susceptibility and weight loss corrosion rates. All EAC specimens and corrosion coupons were machined in the longitudinal direction with the weld metal transecting the specimens at mid-length so that each specimen contained a portion of parent metal, the heat-affected zone (HAZ) and weld metal.
Tensile specimens were installed in proprietary Window-Box Sustained-Load (WBSL) fixtures and loaded to 90% of the actual uniaxial 0.2% offset yield strength at 90°C (AYS90°C), of the heat-specific parent material per ANSI/NACE MR0175/ISO 15156-3:2015. Alternately, FPBB specimens were assembled in four-point bending fixtures and deflected at room temperature to the strain corresponding to 90% AYS90°C of the heat-specific parent material. The stressed EAC specimens and corrosion coupons were exposed to a simulated sour service environment containing up to 0.18 bar H2S and 33,000 mg/L Cl at 90 °C for 720 hours. All EAC specimens passed and weight-loss corrosion rates were < 0.036 mpy.
In addition, Annex A.7.3, ANSI/NACE MR0175/ISO 15156-3:2015 specifies hardness requirements.
Hardness surveys of a girth-weld sample per heat were performed using Vickers hardness tester in
accordance with this Standard for butt welds. Hardness survey of each heat demonstrated that hardness
of base metal, HAZs and weld did not exceed the maximum hardness specified in the Standard.