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g/plumbing • Posted by u/medgas_marcus •

Medical gas brazing — the purge is the whole job and nobody teaches it that way Install

Doing a surgery center addition and training two guys who are both good brazers and both new to med gas. Watching them work clarified something for me about how this gets taught.

They can both braze a beautiful joint. Full penetration, clean fillet, no drips. And both of them wanted to treat the nitrogen purge as a step you do before the real work.

It is the real work. On a med gas line, the joint is not the deliverable — the inside of the pipe is. Copper oxide scale that forms inside an unpurged joint flakes off later and ends up in a ventilator.

What I show them now: braze one joint with purge, one without, cut both lengthwise. The unpurged one looks like the inside of a chimney. Nobody argues after that.

The numbers I hold people to:

  • Nitrogen flow at 3 to 5 CFH, verified with a flowmeter, not a guess at the regulator
  • Purge running before heat, during heat, and until the joint is below 500°F
  • Purge dams on anything longer than about 20 feet so you are not trying to fill a building
  • Verify flow out the far end every single time, because a kinked purge line looks identical to a working one at the tank

ASSE 6010 covers all of this. It is the practical habit of proving flow at the far end that keeps people honest.

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u/weld_wire_wanda •

The cut-it-open demo is the best teaching tool in the trade and it works for more than med gas. I do the same thing for stainless purge on food-grade and pharma work. You can describe sugaring for twenty minutes or you can hand somebody a cut coupon and say nothing.

Also seconding "verify flow out the far end." I have caught a crimped purge hose exactly once and it was on a joint I had already brazed.

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u/pipefitter_pat •

Purge dams — what are you using? I have been cutting them out of soluble paper and it works but it is fussy on larger diameters.

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u/medgas_marcus OP •

Soluble paper for anything under 2 inch, inflatable dams above that. The paper gets expensive fast on big pipe and the inflatables pay for themselves in about two jobs.

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u/backflow_ben •

The framing of "the inside of the pipe is the deliverable" applies to backflow work too and I am going to steal it. A device that tests fine but has debris from a sloppy install upstream is going to fail its next annual and the customer will blame the device.

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u/admin_jake ADMIN •

Pinning this to the sidebar. The distinction between "the joint" and "the inside of the pipe" is one of those reframes that transfers to half a dozen other trades.

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u/water_heater_wally •

Second year apprentice — is med gas something you can get into relatively early, or is it a "get your ticket first" thing? It looks like the most interesting work in plumbing from the outside.

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u/medgas_marcus OP •

ASSE 6010 requires documented brazing experience before you certify, so it is not a day-one thing, but it is not a twenty-year thing either. Get comfortable brazing copper, get your journeyman card, then find a shop that does hospital work and tell them you want it. The certification is a week. The judgment takes longer.

It is genuinely good work. The stakes are real in a way that keeps it interesting.

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