How to Reduce Fabrication Defects in Thin-Wall Stainless-Steel Piping

Thin-walled stainless steel piping fabrication can be challenging. 

Oxidation of stainless steel weld and heat-affected zone.

Fabricators must uphold strict quality control and housekeeping measures to avoid contaminating the austenitic steel. Tools or consumables used for fabricating carbon steel piping must never be used on stainless steel. Stainless steel should be stored and fabricated in an area separate from carbon steel to minimize cross-contamination from fine carbon steel dust particles. 

Flash rusting of stainless weld heat-affected zone.

It is critical to effectively control dross or spatter from cutting torch operations to prevent molten steel from being blown out of the cut and landing on cold steel, as the high heat from the molten slag will damage the stainless steel and lead to oxidation. 

Aligning thin-walled stainless steel pipe to fittings will make your best fitter drag up. Out-of-roundness tolerances in the manufacturing of the pipe and fittings add to the difficulty, which is exacerbated when the pipe is manufactured on one continent and the fittings are from another. Misalignment leads to other defects, such as incomplete penetration, affecting the integrity of the weld.

Internal misalignment is evident in the stainless steel pipe weld, with undercut and incomplete penetration visible.

To combat this, I recommend several key steps: using contractors experienced in fabricating stainless steel weldments, being selective when purchasing stainless pipe and fittings, utilizing internal alignment jigs, employing an orbital welder if possible, and backwelding when necessary and allowed by the WPS. 

Stainless pipe fittings staged for inspection.