This paper describes the development of welding procedures for welding onto in-service pipelines that are used to transport mildly sour produced gas. The development of the procedure focused on obtaining a resulting weldment which met the hardness criterion of Rockwell C22 (Rc22), which is the maximum allowable hardness recommended in National Association of Corrosion Engineers (NACE) MR-01-75 to avoid sulfide stress cracking (SSC) in subsequent service. 1
Several techniques for minimizing weld hardness were investigated. Welds made included baseline single-pass welds at various heat inputs, standard multi-pass welds, multipass welds made at high heat inputs and various temper bead deposition sequences. The optimized procedure involved applying weld metal buttering to the fitting side of the weld joint by the fitting manufacturer prior to installation using preheat. Weld metal buttering was also used on the pipe side of the joint. The buttering was then ground to allow tempering by subsequent passes. A gas tungsten arc weld (GTAW) root pass with an autogenous remelt pass was used to allow tempering in the root region. A unique scheme to facilitate weld toe placement was devised to ensure that these areas received adequate tempering.
A quality assurance method for determining that the hardness criterion had been met was devised. Using this scheme, the suitability of the welding procedure was determined based on a series of measurements on confirmation welds made on the coupon that would later be removed by the action of the hot tap cutter.