ASME Boiler and Pressure vessel Code question

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Is anybody posting on here familiar with ASME BPVC, and ASME B31.3 code for process piping?I'm looking for information on any code requirements for using back purge when welding certain classes of materials, like stainless steel.  I found a clear statement in section IX that backing gas is an essential variable in any TIG or MIG welding procedure.  But there doesn't seem to be any guidance in the code that explains what materials require backing gas.  There are some requirements related to exotics like zirconium, but nothing for austenitic stainless steels or Cr-Mo steels.Is there a separate document where ASME lists this sort of information?  Do they refer to other code documents and I missed the reference?I've searched the AWS forum for clues.  The info I found there suggests that without backpurge, a stainless steel or Cr-Mo(Cr>3%) welding procedure qualification will fail on visual or radiographic inspection, or it might fail a mechanical or corrosion test.  For materials that need backpurge, the sugaring on the root side produces porosity, lack of fusion, or other non=specific defects.We all 'know' that you have to back purge stainless steel piping and some grades of Cr-Mo.  I've found some references in D10.8 and API 582 that require purging for Cr-Mo grades with more than 3% Chromium in the steel.But I can't find a link to ASME B&PV code or B31.X code.  Any help would be appreciated.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:I am in the same situation because my employer has me researching certification for tig welding stainless in accordance with B31.1 & B31.3I have called a few testing facilities and they told me to look into ASME Section 9 code. Could not find much about it without purchasing the code book.Sent from my SM-G920P using TapatalkTOO MANY TOOLS & NO MORE SPACE
Reply:Give John McCracken a call. He knows pipe. Chances are he may know what you're looking for. Pretty knowledgable guy.www.firstratefabricators.comExpert Garage Hack....https://www.facebook.com/steven.webber.948
Reply:Although I do have a CWI, I am by no means a welding expert or welding engineer. Now that that is out of the way, here is what I can add.I am unaware of a ASME document that lists the materials that require a back purge.I has been my experience that the following materials do require a back purge:P5A & P5B materials (2.25Cr, 5Cr, 9Cr), P8 materials (stainless), P42 thru P45 (Monel, Inconel, Hastalloy) The only exception to the above would be for a double bevel weld (i.e. welded for both the front and back sides). In that case a portion of the root pass on the inside (back side) would be ground to sound metal, then the remainder of the joint could be welded.
Reply:@ A_DAB_will_do - you may find some backing gas information for P-class materials in the below docs.  Have not yet poured through them.* ASME B31.1, Code for Pressure Piping, 2007* ASME B&PV Code, IX, Welding and Brazing Qualifications, 2010"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Hello A DAB, I have found that a lot of the time the engineer of record will be the one who will determine, what, how, etc. that question will apply to their specific project. There are some pretty obvious ones, in particular titanium, it is one that has some obvious requirements for back-purge and often times may even specify chamber welding. As to the others: Argon backing, Nitrogen backing, Solar Flux backing, Argon/Hydrogen, and a list of others have and are used for backing with various materials and for different purposes. I am doubtful that you will find a code designated listing, I believe that it will rest with the welding engineer and take into account the intended use of whatever system is being installed. Good luck and best regards, Allanaevald
Reply:It is up to your welding engineer what you use.......  However it must pass the requirements of sec IX, and then be your WPS.  If you can weld stainless without a backing gas, and your WPS meet the requirements of sec IX your go to go.......good luck though...lol.  I worked for company "A" who's WPS stated we had to weld 2% chrome with a backing gas...... That was the law for company "A".......as a matter of fact the backing gas had to be argon.  Couple years latter I was working for company "B". There WPS didn't require a backing gas for chrome.....as long as I follwed the WPS I was good.It all boils down to the procedure that was developed by your engineer, that was proven to meet the requirements of the code, is what you have to follow for that given company.  The code is not ment to hand cuff you........we as welders, need to know how to work the code.....Hope this makes sense........Interprovincial RedSeal Welder and SteamfitterMiller Maxstar STL 110vMiller Blue Star DX 185Lincoln 180
Reply:Originally Posted by 7A749Give John McCracken a call. He knows pipe. Chances are he may know what you're looking for. Pretty knowledgable guy.www.firstratefabricators.com
Reply:He would be the guy to ask Expert Garage Hack....https://www.facebook.com/steven.webber.948
Reply:Originally Posted by butrbalAlthough I do have a CWI, I am by no means a welding expert or welding engineer. Now that that is out of the way, here is what I can add.I am unaware of a ASME document that lists the materials that require a back purge.I has been my experience that the following materials do require a back purge:P5A & P5B materials (2.25Cr, 5Cr, 9Cr), P8 materials (stainless), P42 thru P45 (Monel, Inconel, Hastalloy) The only exception to the above would be for a double bevel weld (i.e. welded for both the front and back sides). In that case a portion of the root pass on the inside (back side) would be ground to sound metal, then the remainder of the joint could be welded.
Reply:Originally Posted by ManoKai@ A_DAB_will_do - you may find some backing gas information for P-class materials in the below docs.  Have not yet poured through them.* ASME B31.1, Code for Pressure Piping, 2007* ASME B&PV Code, IX, Welding and Brazing Qualifications, 2010
Reply:Originally Posted by aevaldHello A DAB, I have found that a lot of the time the engineer of record will be the one who will determine, what, how, etc. that question will apply to their specific project. There are some pretty obvious ones, in particular titanium, it is one that has some obvious requirements for back-purge and often times may even specify chamber welding. As to the others: Argon backing, Nitrogen backing, Solar Flux backing, Argon/Hydrogen, and a list of others have and are used for backing with various materials and for different purposes. I am doubtful that you will find a code designated listing, I believe that it will rest with the welding engineer and take into account the intended use of whatever system is being installed. Good luck and best regards, Allan
Reply:Originally Posted by Skull1It is up to your welding engineer what you use.......  However it must pass the requirements of sec IX, and then be your WPS.  If you can weld stainless without a backing gas, and your WPS meet the requirements of sec IX your go to go.......good luck though...lol.  I worked for company "A" who's WPS stated we had to weld 2% chrome with a backing gas...... That was the law for company "A".......as a matter of fact the backing gas had to be argon.  Couple years latter I was working for company "B". There WPS didn't require a backing gas for chrome.....as long as I follwed the WPS I was good.It all boils down to the procedure that was developed by your engineer, that was proven to meet the requirements of the code, is what you have to follow for that given company.  The code is not ment to hand cuff you........we as welders, need to know how to work the code.....Hope this makes sense........
Reply:Well A DAB, if it had been 30 years ago or so you would likely "do as the Romans do" and go with the consensus of the trade. But in our age of lawyers, legality, etc. you better have a bit more to base a decision on. As I did mention though, the codes are really mum on these sorts of things as there are just too many exceptions where the purpose justifies a different approach than those that we may be familiar with. When I was in school (a day or 2 ago) I was contemplating going on and getting into nuclear pipe welding. At that time they were welding carbon with a full argon purge and GTAW all the way out in some instances. By today's standards that would probably not be the norm although possibly within the nuclear area it may still be a desirable method. I seem to recall hearing that some folks who are welding on chrome will use a nitrogen purge, however, as you have already eluded to, this may just be an approach that some folks take and you would be hard pressed to find it etched in stone anywhere. I'll be following this as it is definitely good information to know. Thanks for bringing it up as a topic. Best regards, Allanaevald
Reply:@ A_DAB_will_do - if there is not any known code specifying the use of Ar backing gas, seems to me that you should adopt 'best practices' and use Ar shielding on the P91 piping.  Certain you' ve seen/read the P91 tech ref from SperkoEngineering, but perhaps the P91/T91 Handbook by Vollourec-Mannsfield (1999) may shed some light.  Have not been succesful in locating a .pdf of the Handbook.If you are the defacto Engineer of Record, then why would there be an issue in having the WPS callout the requirement for backing gas?  Understand the impact is cost/schedule to your client.  However, all the tech refs.......and other WW threads (2009) discussing welding P91 discussed internal shielding.  Is there a risk or negative impacts resulting from using Ar backing gas?  Don't believe so.Totally tracking on your desire to locate a REQUIREMENT.  Staunch proponent of Requirements 101.  Good stuff."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Originally Posted by ManoKai......Understand the impact is cost/schedule to your client.