Welding P22 sch 80 20" Pipe

[frankcc]

Anyone, I have a set procedure to follow on this job I am working on. Using ER90SB3 for the TIG root and E9018B3 Stick to fill. I was wondering how others would do this job. What temperature do you preheat to and do you prefer gas backing for the root run ? I have several butt welds to make and I have mostly welded P11 in the past so this P22 Material I am told has to be done in a careful manner. The job will be heat treated when finished along with xray. Any thoughts or comments would be greatly appreciated. FrankCC

[Stu Bass]

All the code work I've done on boilers they required a purge for anything 9018 and above. Preheat was most of the time about 100 degrees or just hot to the touch. Every once and a while some inspectors would want as much as 250 degrees. With the b3 wire I would say yes you definately would want a purge for your open root. stu bass

[frankcc]

All the code work I've done on boilers they required a purge for anything 9018 and above. Preheat was most of the time about 100 degrees or just hot to the touch. Every once and a while some inspectors would want as much as 250 degrees. With the b3 wire I would say yes you definately would want a purge for your open root. stu bass

I have to preheat to 350 Degrees because of the thickness in the Tees and Elbows. Normally I tape the joints closed and use purge dams to keep my gas backing in place. With this preheat holding the argon backing inside to the desireable amount seems difficult. Tape won't stick at this Temp. Some say argon backing is not necessary but I favor using it. Purging seems to be relatively simple on small pipe sizes, but with high preheat and larger pipe sizes I would like to know how you or anyone would handle this situation? I like to feel a positive but light flow of gas backing before I start welding. Any thoughts on purging and backing would be of great help. Thanks, Frank CC

[Michael Albro]

Frank I pre heat p-22 to 400 with interpass not to exceed 600. but even with the small socket welds I have the heat treat people there and they put there heating elements and thermo coulples on and preheat it for me and tell me when the temp is good. also tell me when temp is getting close to 600 so I can stop and let it cool some. of corse I have a temp stick in my pocket too. so I can check it myself.This allows the heat treater to go strait into the PWHT process as soon as Im done with the weld. also gives a graph read out of the whole process from preheat to post weld heat treat. And yes a P-22 open root butt joint I would purge the root side with argon, and leave it on at least through the hot pass.

Hope this helps, Mike

[frankcc]

Frank I pre heat p-22 to 400 with interpass not to exceed 600. but even with the small socket welds I have the heat treat people there and they put there heating elements and thermo coulples on and preheat it for me and tell me when the temp is good. also tell me when temp is getting close to 600 so I can stop and let it cool some. of corse I have a temp stick in my pocket too. so I can check it myself.This allows the heat treater to go strait into the PWHT process as soon as Im done with the weld. also gives a graph read out of the whole process from preheat to post weld heat treat. And yes a P-22 open root butt joint I would purge the root side with argon, and leave it on at least through the hot pass.

Hope this helps, Mike

My main problem is how to purge large pipe sizes with high preheat Temps. I normally tape the open root closed to hold my backing gas and remove it as I weld. With the tape in place it insures I get a positive flow. The tape falls or burns off at 350 and I lose the purge I need to insure a good under bead. How do you get a good purge with the root open. I tried increasing the flow and even added an extra hose to compensate for the root gap opening. I still have a week to figure this out and I appreciate any help I can get. Frank CC

[Michael Albro]

Frank what I do is, Masking tape works great with stainless but like you said with the preheat it melts. So my inside dams are kept far enough away that the heat doesn't affect them. and on the outside rather than using masking tape I stuff Kaowool or some ceramic fiber insulation in the joint to seal it and remove it as I go. This is the same stuff they rap there heating elements with when heat treating. I also have a high output regulater I use for purging a large area. smaller flow meter regs. just don't put out enough gas. An oxygen reg will work if you change out the fitting or have an adaptor.

hope this helps, Mike

[Slyfox1956]

You could try aluminum HVAC tape used for wrapping heating ducts or they do make a fire tape at 3m. We make hot welds with the fire burning and it stays in place with no problems. It is a fire retartent tape so the weld hardly affects it as you pull it off.

[frankcc]

Frank what I do is, Masking tape works great with stainless but like you said with the preheat it melts. So my inside dams are kept far enough away that the heat doesn't affect them. and on the outside rather than using masking tape I stuff Kaowool or some ceramic fiber insulation in the joint to seal it and remove it as I go. This is the same stuff they rap there heating elements with when heat treating. I also have a high output regulater I use for purging a large area. smaller flow meter regs. just don't put out enough gas. An oxygen reg will work if you change out the fitting or have an adaptor.

hope this helps, Mike

This coming week I will give everything a try and see how it works out. Purge dams are in place far enough away from the heat. Tried kayowool already, it was difficult to hold in the joint and also a bit dusty. High temp tape is my next try. It is good to 800 degrees. I will also try a different regulator to increase the output like you suggested. I will let you know how everything works out. Its nice to talk to people with hands on experience in the same kind of work I do. Thanks again, Frank CC

[frankcc]

You could try aluminum HVAC tape used for wrapping heating ducts or they do make a fire tape at 3m. We make hot welds with the fire burning and it stays in place with no problems. It is a fire retartent tape so the weld hardly affects it as you pull it off.

Your reply must of came up while I was getting back to Mike. I will be trying a brand of high heat tape that should arrive Monday. I don't know what brand it is yet, I was told it would withstand the preheat and a lot more. Thanks, Frank CC

[frankcc]

Your reply must of came up while I was getting back to Mike. I will be trying a brand of high heat tape that should arrive Monday. I don't know what brand it is yet, I was told it would withstand the preheat and a lot more. Thanks, Frank CC

If this would be of any help to anyone. I am using a high temp tape from ESAB welding products. Part No 693000341. This tape is 3.375 inches in width. It stays in place with no problem with a 400 degree preheat. This tape has really helped me out on this job. FrankCC

[Michael Albro]

I will have to try it next time Frank, thanks