EFFECT OF PURGE QUALITY ON THE PROPERTIES OF STAINLESS STEEL WELDMENTS FOR PRESSURE PIPING APPLICATIONS FOR OIL, GAS AND POWER GENERATION INDUSTRIES

Stainless steel pressure piping and components joined by welding are commonly used for applications in the oil, gas and power generation industries. Owner technical specif cations often reference AWS D18.2 as a guide to weld discoloration levels inside piping. This standard was designed for hygienic applications such as the food industry and is not practical for other industrial applications. A base line comparison to AWS D18.2 was produced using “bead-on-plate” welds, base materials and procedures that are typical for fabrication and maintenance of oil, gas and power generation facilities. Then several butt welds were produced with GMAW and GTAW process for the root pass followed by FCAW process for fill and cap pass with an argon purge quality of 50 ppm and 500 ppm oxygen. The degree of weld discoloration and microstructure evolution was evaluated for various levels of purge quality. Optical and Scanning Electron Microscopy (FEG-SEM) equipped with Energy Dispersive Spectroscopy (EDS) chemical mapping, ferrite testing and micro-hardness were used to assess the microstructure. The results show that surface discoloration is further increased at the same level of purge quality when compared with AWS D18.2. The amount of inclusions in the weld metal increased with increasing the amount of oxygen in the purge. There were minor changes in ferrite volume and hardness with purge quality.