During fabrication of piping systems discoloration (heat tint) in access of that accepted by welding standards such as Norsok M-601 is sometimes experienced.1 This is normally a result of insufficient purging gas. The effect on mechanical properties and corrosion resistance were investigated. Pipe spools made from 22Cr duplex stainless steel, 25Cr duplex stainless steel and titanium Gr. 2 were welded using argon purging gas with mixed-in oxygen at various concentrations to simulate insufficient purging. The mechanical testing included tensile testing, impact testing and hardness measurements while the corrosion testing included ASTM G482 – Method A pitting tests, critical pitting temperature measurements in simulated seawater and critical pitting potential measurements in simulated well fluids according to ASTM G61.14

The results from tensile testing, impact testing and hardness measurements showed that the tested materials were virtually unaffected by the purging gas conditions, except when welded with no purging gas at all. The corrosion testing also showed that the materials were more or less unaffected by the purging gas conditions, both in seawater service and in hydrocarbon service. The main conclusion of the work is that the integrity of piping systems in 22Cr duplex stainless steel, 25Cr duplex stainless steel and titanium Gr. 2 does not seem to be compromised by insufficient purging, as long as some level of purging gas is used for butt welds.

Subject
Discoloration, Test methods, Materials, Welding, Simulated seawater, Fluids, Purging, Pitting, Oxygen, Titanium, Corrosion resistance, Duplex stainless steel, Critical pitting potential
Keywords:
Welding, Purging gas, Heat tint, Duplex Stainless Steel, Titanium, Pitting Corrosion, Seawater systems, Hydrocarbon systems
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2021
Association for Materials Protection and Performance (AMPP)
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