P91 Heavy wall

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I was wondering if anyone has pointer's on tig welding P91 chrome heavy wall pipe?
Reply:If you are welding at a power plant shutdown, the owner will SPECIFY how, and what has to be done proceedure wise, UNLESS you are doing it personally to keep your head in it (keeping in practice).then, you'll have to go to airgas, or other welding supply and tell them what you need as far as cut length wire for heliarc welding. in your case P91 chrome. they'll fix you up. normally its 1 heliarc root pass, 1 or 2 hot heliarc fill passes, and the rest stick all the way out to the cap. depending on the pipe diameter either 3/32 or 1/8" rod is the norm for this.hope this helps.mike.
Reply:The most important thing when welding P91 is getting a good purge for the root.  P91 is very difficult to root if you do not have nearly 100% argon on the back side, and I prefer a decent flow volume.  When rooting, I take the largest gap the QC will allow, up to 1/4", and the smallest wire available on site (usually 3/32).  I run the root between 60-80 amps and keyhole dabbing wire as I go.  Under a purge, the metal will tend to flow to the inside of the pipe and will not be prone to suck back as much.  A lot of folks try to feed or walk over the wire with P91.  I'm not saying this is wrong, as it does work for some, but you definitely know the wall is breaking down when you keyhole.  P91 can be pretty hard to breakdown walking over the wire or feeding it.  After rooting, I'll usually run 3 or 4 hot passes before switching to stick.  The first stick pass I run is always 3/32 just to be sure not to disturb the root or worse, blow through.  Then I'll usually switch to 1/8 (depending on pipe size).  Depending on the brand and type of Stick Rod (9018, 9015, etc.), The slag can be difficult to remove.  The biggest thing to remember when stick welding is keep it clean, very clean.  Don't be afraid to wire wheel after every pass and grind any high spots, narrow valleys, etc.  That hard slag can get trapped pretty easily. Basically, Good Purge, Keyhole, Keep it very clean.On Edit:  Forgot to mention...Heavy wall Tig Cups will help GREATLY when rooting and hot passing.  The longest ones I have are #8, 10, & 12 cups XXL Length.  They are about 6" long.Last edited by bagofdimes; 01-12-2010 at 12:01 AM.
Reply:A TON of P91 gets welded on this site, as our entire main steam system is all heavy wall P91.The 9015 rods dig a little harder than the 9018.  Watch out for wagon tracks along the sidewalls.  Grind as necessary.  Be conservative on any heavy wall joint.  One of our welds took 30 days start to finish with two guys on them due to busted info shots and machining to excavate a LOT of trapped slag.This one is a biggie - a lot of suppliers will ship P91 spools out with deoxiluminite primer on the face of the bevel.  This stuff is HORRIBLE for the joint, despite what the manufacturers tell you.  It often contributes to lack of fusion, and creates dirty, scaling weld pool.  It cannot just be wire brushed off.  Make SURE that joint has been wire wheeled, cleaned with MEK, and then hit with a tiger paw or flap wheel.  On a number of instances, we have actually had to take a hard grinder to the bevel to get it clean enough.  Same goes for the land and counterbore.  Your welding department/engineering should have a procedure for addressing this.On P91, try to run your stringers from the outside towards the center, rather than straight across the joint.  Some WPS's will specify this.  It promotes tempering of the heat affected zone.  If you're welding with a partner, ask QC/welding supervisors if they have any amber heat tape.  It's a see through amber tape that won't melt on the pipe.  This lets us put a purge on the joints while having someone else look you in on the root and hot.
Reply:Hey Supe...you guys hiring?
Reply:I kinda skimmed the thread, but I vote, purge and TIG the root, the cap with stick 9018 I am guessing.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:When testing to re-certify our 2 1/4% chro-moly we are not aloud to purge to simulate a "real life" situation in the coal fired boiler where a purge is just not practical. Of course your going to get a more asthetically sound weld when you add a purge. Just be sure your adding lots of material while your doing your root to avoid suck back.
Reply:Solar flux is always an optionDisclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Originally Posted by bagofdimesHey Supe...you guys hiring?
Reply:you could have a look to the below link:http://www.weldinguide.com/gdanastas...c.php?f=2&t=10