Stainless steel welding that keeps the metal stainless

Stainless resists rust because of a thin chromium-rich film on the surface. Welding can damage that film, so the joint is where stainless parts most often fail in service. This page covers the weld, the heat and the cleanup. How stainless machines is a separate subject on the material page.

At a glance

• Heat kept down to protect corrosion resistance
• Clean joints, with tools used only on stainless
• Strainers and baskets seam-welded to flanges
• Stainless parts for food processing plants
• Ventilation and fume control as a standard part of the work

Why heat is the enemy of stainless corrosion resistance

Stainless gets its name from chromium. When the metal sits too long in a certain heat range during welding, chromium can combine with carbon near the weld, and the area beside the weld loses some of its protection. This is called sensitization, and it is the reason a stainless weld can rust or corrode in service even though the base plate does not.

The practical answer is controlled heat: stringer passes instead of wide weaves, time to cool between passes, and filler suited to the grade. Low-carbon grades are also chosen for welded parts for this reason. A heat-affected zone is always there. The job is keeping it narrow.

Cleanliness and finishing the joint

Carbon steel dust, grinding dust or a steel wire brush can embed iron in a stainless surface and cause rust spots later. Stainless is cleaned and ground with tools kept for stainless only.

After welding, the heat tint around a weld is a sign of a disturbed surface. In many food and washdown applications the joint is cleaned back and passivated, a general practice that restores the protective film. Tell us at quote time if a part has a finish requirement, so the plan includes it.

Distortion and thin sheet

Stainless expands more than carbon steel and conducts heat poorly, so it warps easily, especially in thin sheet. Perforated strainer sheet seam-welded into a cone and then to a flange is a good example: the welds have to be placed and sequenced so the shape stays round and the flange stays flat.

Food-plant parts and fume control

Our services list includes steam tubes, titanium screws, handles and stainless steel knives made for a food processing plant. That kind of work shows why joints must be smooth and clean.

Welding stainless creates fume that can contain hexavalent chromium, which is why shops ventilate and follow the exposure rules in OSHA 29 CFR 1910.1026. You can read more in our post on the OSHA rules behind stainless welding.

• Send the grade if it is stamped or on the drawing
• Say whether the part sees food, water, chemicals or heat
• Include photos of the break or a drawing of the new part