Welding C/S at high temperatures????
Welding C/S at high temperatures????
(OP)
We have a refractory lined, carbon steel collection header which has sustained localised refractory damage and subsequent hot spots. We are unable to shut the process down to repair the refractory so I want to investigate an on-line “temporary” repair.
I am proposing to weld nozzles onto the vessel on-line in the areas of localised refractory damage (temps up to 930 OF when steam cooling is removed), hot tap into the vessel and inject liquid refractory into the void areas. To make it more interesting, the vessel contains hydrogen gas at approx 2000 kPa (290 psi).
Things I am wondering are;
· Will welding at these high temperatures cause excessive stresses in the joint when the system is eventually cooled down (hopefully in a year or so).
· Can welding be successfully carried out at these shell temperatures?
· Will the existing refractory be damaged by welding (shell is 16mm thick).
Any help on this subject will be appreciated.
Thanks
I am proposing to weld nozzles onto the vessel on-line in the areas of localised refractory damage (temps up to 930 OF when steam cooling is removed), hot tap into the vessel and inject liquid refractory into the void areas. To make it more interesting, the vessel contains hydrogen gas at approx 2000 kPa (290 psi).
Things I am wondering are;
· Will welding at these high temperatures cause excessive stresses in the joint when the system is eventually cooled down (hopefully in a year or so).
· Can welding be successfully carried out at these shell temperatures?
· Will the existing refractory be damaged by welding (shell is 16mm thick).
Any help on this subject will be appreciated.
Thanks





RE: Welding C/S at high temperatures????
RE: Welding C/S at high temperatures????
RE: Welding C/S at high temperatures????
Assuming that the gas is diatomic and not monotomic hydrogen, welding can be successfully accomplished provided the interpass temperature is limited only slightly greater than the 930 F temp with low heat input GTAW/SMAW processes.
If refractory is presently damaged as you have indicated, welding may increase the damage area somewhat.
The weld will lack the toughness normally seen for such welds and may be unsuitable for your requirements. You should qualify your welding procedure to simulate the "preheat/interpass" conditions. You should also "qualify" your welder under similar simulated conditions including welding a nozzle to pressurized (with air) pipe to give him/her that "warm" feeling that all will be safe.
RE: Welding C/S at high temperatures????
I posted this in another thread.
H2 in line is dangerous no matter what state it's in. I think this is too dangerous to attempt a weld or use a hot tap machine, which is going to damage more refractory, on the line.
If you get a H2 leak and the resultant fire you will have a melt down of anything close.
H2 isn't interesting it is very dangerous.
RE: Welding C/S at high temperatures????
RE: Welding C/S at high temperatures????
We have had an experienced metallurgist give us alarm/high alarm/shutdown temperatures and we are monitoring them continuously. At the moment the temps have stabilised but I wanted a plan in place in case they got worse. Ideally the plan wouldn't involve shutting down but this may turn out to be unavoidable.
Thanks again.
RE: Welding C/S at high temperatures????
We have actually used water sprays (mist) and steam on the same material at approximately your temperature. Just keep an eye on the line as H2 can make small hole very large quickly.
Your idea has does have merit as we do it all time on the plenums of an low pressure oxidizer system that operators at 3000°F. When we get a hot gas leak at break in the shell or a "stinger" in the shell we weld on encompassing 1/2" pipe nipples and blow a hole in shell and inject a phosphate based hydraulic refractory very carefully as not to push off the remaining internal refractory.
One other thing we have done in these plenums is the application of process know as refractory welding. This is repairing large areas of failed refractory and burn through without cooling below 2000°F. A little expensive but we avoided 3 days coming down and 3 days coming on stream. Since we didn't shut the unit down we suffered no recordable downtime.
Hope it last until you can have an outage.
Good luck.