Environmental Effects on Fitness-for Service Parameters For 1% Nickel Steel Pipe Welds with Preferential Weld Corrosion Damage

Abstract

This study presents slow strain rate, notched slow strain rate and compact tension test data on the changes, due to environmental exposure, in mechanical properties and fracture toughness of 1% nickel steel welds in API 5L X-52 surface facilities piping. These strength and toughness parameters serve as input for fitness-for-service analyses of preferential weld corrosion (PWC) damage as either corrosion grooves or crack-like flaws. In 1% nickel steel welds, in CO₂ environments, toughness loss of ca. 35% was observed even in the absence of H₂S. Toughness loss of ca. 42% was observed even at H₂S levels as low as 100 ppm. Yield and tensile strength were less affected, but strain to the onset of plastic instability may be reduced, which is a critical parameter for finite element analysis of PWC zones as corrosion grooves. Observed environmental effects depend strongly on whether the weld metal is cathodic or anodic to the nearby base metal.