What oxygen does to a weld root
When stainless steel, duplex or titanium is heated past its critical temperature, any oxygen still present in the pipe reacts with the hot metal. The result is an oxide layer on the inside of the joint: discoloured at best, and at worst the rough, crystalline surface welders call “sugaring”.
That layer is not cosmetic. It removes chromium from the surface, destroys the corrosion resistance the alloy was specified for, and creates crevices where product, bacteria and cleaning chemicals collect. In hygienic and high-purity systems it is a rejection.
The traditional answer, and its cost
The conventional fix is to flood the entire pipe run with argon and wait. On a long spool that means a very large volume of gas, a long wait before striking an arc, and repeat purges every time the line is broken into.
The MJS approach
MJS purge systems seal only the weld zone. Two inflatable dams form a short chamber either side of the joint, inert gas displaces the oxygen inside it, and an oxygen monitor confirms when the atmosphere is ready. Less gas, less waiting, and a measurable, repeatable result you can certify.
Weld purging, answered
How low does oxygen need to go?
It depends on the material and the specification. Many stainless applications target below 0.1% (1000ppm); titanium and high-purity work often calls for far lower. The Handy Purge 100 measures to 0.01%, so you can weld against a number rather than a guess.
Which system suits my pipe size?
The Double Bag Purge System covers 2″ to 48″ and handles around 90% of traditional purge applications. Above roughly 8″, Rapid Purge is usually the faster option, covering 8″ to 80″ with a thru-bore design that cuts purge volume dramatically.
What if the pipe is pre-heated?
Both families have a heat resistant variant. Standard Purge HT is jacketed for 350°C continuous and 500°C short-term; Rapid Purge HT is rated to 250°C.
Are the systems reusable?
Yes. The dams deflate and withdraw after each joint, and friction-free coatings let them move through bends and elbows to the next weld.
Do I still need to monitor oxygen?
Monitoring is what turns a purge into evidence. Without it you are estimating; with it you have a reading you can record against the joint.