American Welding Society Forum
Working for an aerospace company and they are setting up in a new shop. They are wanting to run the argon lines from the main bulk argon supply to the weld booths using black pipe.
In the old facility everything was copper piping, which I thought to be suitable.
I'm concerned that the argon quality will suffer being transported through mild steel piping, the company would like to use black pipe as a cost saving measure.
NADCAP AC7110/5 G.2 asks, "Are gas lines and tubes used for the transportation of shield gas made from neoprene, PTFE, or material suitable for gas being used?"
The handbook references the following as a supplement to this question
Intent: To avoid using contaminated gasses due to leakage because of incorrect or poor quality / porous material.
Acceptable Objective Evidence: Auditor to visually check gas lines. If gas lines are made of suitable material and no degradation is visible, no further checks are required. If the tube material is incorrect and / or it shows signs of degradation, supplier must demonstrate that the gas has not been contaminated as a result of this. Examples of how this could be demonstrated are oxygen meters, dew point meters or strike plates etc.
Has anyone dealt with this before? I cannot find anything that states I cannot use black pipe, I just don't think it's good practice.
One question; will the joints be welded or threaded?
The black iron isn't porous and the argon is inert. I might be inclined to use ASTM A106 because it is seamless. There is a potential problem of leaks if threaded fitting are not properly installed. If the welds aren't properly made, they could leak. Copper tubing could suffer the same problems if the joints are not properly made. The solution? Make sure the installation is done properly and perform leak testing to verify the system is leak free.
Thanks for the response. I will check on the material, they are intending on using threaded connections with Teflon tape.
The quality of the threads does make a difference. If the die is worn, it will tear the threads and a quality seal is more difficult to attain.
I've used both the teflon paste and tape. I think the paste does a better job overall, but it can be messy. Just an opinion.
we are dealing with it right now. We made the decision to use 304L sch. 10 material mainly because of concerns of C.S getting internal rusting issues over the years and our shop being in South Texas where a constant high humidity exists. We are using SW fittings with limited screwed connections. A lot of what I'm saying is from lessons learned. My previous company that I worked for had a fab shop in Freeport Texas. We had a CS argon header system and were constantly dealing with leaks and rust contamination. The system had been in place for years. As we cut it apart to replace sections there was a lot of rust in certain sections of the pipe. It was not in all sections but it was enough to cause problems.
Did they ever determine why there was moisture in the system? The moisture content of argon that meets AWS 5.32 is very low, something like 17 ppm. That shouldn't be high enough to cause a problem with rusting on the ID of the pipe. Sounds like there is a bigger problem than simply using carbon steel pipe.
Yes. Mainly due to system leaking down. The shop supervisors would shut the system down on Thurs. (working 4 10"s) The system had leaks and would leak down and at 98% humidity in South Texas the system would get moisture. We know this because of the drain valves when opened would have moisture. Over the years parts of the system just deteriorated. To be clear we did not perform an RCA but this is what we speculated to be the cause. With that lesson learned we are using SS pipe with SW connections. In another post it was recommended that we consult our gas supplier. Well, we did and they concurred with our selection.
Using the stainless piping for the system may eliminate rust, but it doesn't eliminate leaks that allow moisture to enter into and to condense in the system. Both the moisture and air leakage contaminates the shielding gas. Several welding standards specify the shielding gas to have a dew point of less than -40 degrees F, condensate in the piping system is going to mean your dew point is going to be much higher for a period of time until all the moisture has evaporated.
Ask your gas supplier for their standard/recommendations.
Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill