A sanitary weld is the result of a controlled process, not luck. Skip a step and the joint will look identical from the outside while failing inspection on the inside. Here is how the work is actually done in food, dairy and pharmaceutical plants.
1. Joint Preparation
Sanitary tubing is cut square — typically with a portable cutoff saw or a precision tube cutter — never with an abrasive wheel that contaminates the surface. Ends are deburred and faced so the two pieces meet with no mismatch greater than the ASME BPE limit. Surfaces are cleaned with a dedicated stainless wipe and a non-chlorinated solvent.
2. Inert Gas Purge
Pure argon is introduced inside the pipe to displace oxygen on the root side of the weld. Without a purge, the back of the weld oxidizes and forms "sugaring" — a flaky black or brown surface that traps product and harbors bacteria. Purge dams or soluble paper are placed near the joint, and the system is purged until oxygen drops below ~25 ppm (verified with an oxygen analyzer for high-purity work).
3. Tack and Align
Three to four small autogenous tack welds (no filler metal) hold alignment. A clamp ensures the tubes are concentric and square. Any mismatch here shows up as concavity or misalignment in the finished weld, both of which fail BPE acceptance criteria.
4. The TIG Weld
Sanitary tubing is welded autogenous — no filler metal added — with the base material melted and fused. Heat input is tightly controlled. Too hot and the weld is wide, concave and discolored. Too cold and the root does not fully fuse. The torch travels at a steady speed with the welder watching the puddle through a magnifier.
5. Borescope Inspection
After cooling, a borescope camera is fed inside the pipe to inspect every weld interior. Acceptable welds are bright silver to light straw in color, fully fused, with no concavity beyond the BPE limit and no undercut. Any blue, purple, gold or black coloring indicates inadequate purge and the joint is cut out and redone.
6. Documentation
Every joint is recorded on a weld log: weld number, welder ID, date, material heat numbers, inspection result and a borescope photo if the spec requires it. The weld log ties to a weld map of the system — auditors can trace any joint in the line back to the welder and the inspection.
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We follow this sequence on every joint, in every plant, nationwide.