Abstract

Pipelines for transport of oil and gas in Arctic areas are subjected to some extreme challenges; among these being low temperatures. Thus, the steel behaviour with respect to the ductile to brittle transition will be important. Moreover, when the design temperature falls down to -50 to -60°C, the toughness of the weld metal may become a critical factor. In the present investigation, submerged arc welding was performed using two different wires (Wires 1 and 2), using 23.7 mm base plate corresponding to API X80 quality. The test programme included tensile and notched tensile testing, Charpy V notch testing, and finally, SENB05 (bending with a/W = 0.5) and SENT02 (tension with a/W = 0.2). The tensile test results confirmed that the base metal and weld metal yield and ultimate strength increases with falling temperature. The Charpy V results showed high values for Wire A with all individual values above 50 J. The fusion line (FL), FL+2 mm and FL+5 mm had even higher toughness than the weld metal. The CTOD testing confirmed the trend from Charpy V. Wire A gave good weld metal results (SENB05 > 0.3 mm), while wire B possessed low toughness (≤ 0.11 mm). Constraint effects are evident by comparing the results obtained from SENB05 and SENT02 weld metal testing.

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