Abstract
This paper presents mechanical and corrosion resistance properties of stainless steel weldment with root pass deposited using GMAW modified waveform short circuit welding process without backing gas, referred to as No-Backing Gas (NBG) welding process in this paper. While other welding techniques exist that also omit backing gas for similar applications, the term No-Backing Gas (NBG) is employed here for simplicity’s sake. Data has been obtained using 316LSi stainless steel filler metal on 304L stainless steel base metal. Test work included a baseline coupon, deposited using a GTAW root pass back purged with inert gas, as this has traditionally been the industry best practice for welding stainless steel pipe to minimize internal surface contamination and oxidation. NBG test coupons were welded using GMAW-P for second pass and FCAW for remaining passes. Baseline GTAW coupon was welded using GTAW for second pass and FCAW for remaining passes. Test work included ASME BPVC Section IX required tests, Charpy v-notch impact test, ferrite test, macrograph, hardness examination, and corrosion immersion tests ASTM A262 Practice C and ASTM G48 Modified Method E. The obtained results were assessed for cryogenic temperature application requirements of ASME B31.3 Process Piping Code and for mildly corrosive service applications (see Note-1 below). The paper also discusses the challenges associated with ASTM G48 Method E for testing of 304 stainless steel weldments and use of a modified, fit-for-purpose G48 method to evaluate results. Furthermore, the authors share lessons learned and recommendations from their experience on a recent project on which NBG welding was extensively used on stainless steel piping.
Note-1: Corrosion tests are based on standardized solutions and may not be representative of all applications. Users should establish their own qualification for the intended service application.
