My shop does a lot of work with chrome moly's and it would be unthinkable for us to weld without preheat. Perhaps this may be due to the fact that along with the high Cr, the alloys we use also have a high C content or high CE value. Even on minor surface repairs we will require some amount of preheat, whatever the WPS wants.
I presume that you are talking about the low alloy piping; I have done few power plant projects which have a lot of alloy piping, for this kind of materials the preheat mandatary and only exempted for alloy with Cr less than 1/2% only.
cheers
Alex
If memory serves I've run onto some specs that neglected to make it explicit. When I made a point of addressing it they corrected the oversite.
In code work I have seen none. In the real world, CrMo tubing frames made of thin material could be welded without preheat. Oxy Acet welded CrMo could be welded without preheat :) .
Here is an interpretation . I don't know if its still current. I don't have a section I with me so I am not even sure the context of the interpretation.
Interpretation: I-83-66
Subject: Section I, PW-39, Postweld Heat
Treatment of Seal Welds
Date Issued: November 11, 1983
File: BC83-116
Question (5): Is preheat required for welds of
socket welded fittings permitted by PW-415 for
P-No. 1, P-No. 3, P-No. 4, and P-No. 5 materials?
Reply (5): Preheat is not mandatory for such
socket welds between P-No. 1, P-No. 3, P-No. 4,
and P-No. 5 materials. However, refer to
Appendix A-100 for nonmandatory guidelines.
There may be situations in which a reduced preheat can be used. Some processes are more forgiving than others. GTAW is by nature a very low hydrogen process and in some cases such as temper bead welding may produce satisfatory results without the typical code required preheat as is needed for other processes. That doesn't mean the code says its ok. But that also doesn't mean its not possible.
Again, this may not be indicated in any code and this thinking may not apply to the materials you listed above.
Here is a paper related to P1, P3 materials that addresses reduced preheat for temper bead welding using mechanized GTAW .
http://www.epriweb.com/public/GC-111050.pdf
Thanks everybody. Thats what I was looking for.
Here is a paragraph from B31.1
131.5
For inert gas tungsten arc root pass welding, a lower
preheat temperature in accordance with the temperature
established in the WPS may be used.
Just to add what Gerald already indicated... The very reason for applying the use of a tempering bead technique is to eliminate the need to reqiure high post weld heat treatment even though in certain specific situation PWHT cannot be avoided completely.. However, the greatly reduced amount of required temperature for PWHT is advantageous in some situations such as welding on HY-80 or similar steels where dimensional tolerances need to be closely monitored, and a lower preheat temp is desirable. ;)
As Gerald and others in here know, the USN has been using these practices way before EPRI came out with their reports and findings on this subject. :) :) :)
Respectfully,
Henry
Guys, I appreciate your help but I am trying to build a case here for preheating Low alloy steel for welding. I am not concerned about tempering bead techniques. Only pipe welding.
We have some people on my project that do not believe preheat is important for pipe welding.
So my question is, is preheat important for pipe welding on low alloy steels and P-1 material over 1" thick?
NDT III,
You don't mention what code but if you are talking chromolly piping then it is quite posibly B31.1.
If that is the case Section 131.4 clearly states minimum preheat temps for P1,P3,P4,P5 & 5A,P6,P9A & B and P10I. None of those materials listed can be welded without preheat and be in accordance with the code.
AWS D10.8 Recommended Practices for welding of Chromium-Molybdenum Steel Piping and Tubing lists under "Suggested minimum preheat temperatures for various base metal combinations for wall thicknesses not exceeding 3/4"."
1/2 to 1 1/4 CrMo as 250 degrees F minimum.
2 to 3 CrMo as 300 degrees F minimum
5 to 9 CrMo as 400 degrees F minimum
Hope that helps,
Regards,
Shane
NDT-
I feel your pain. All too often I have to engage in needless debate with people who don't care and don't want to listen to "requirements". If they don't accept your metalurgical explanation on why preheat is a good thing then you have to point to the governing specs and end the argument. If you are working on power pipeline, then for P-1 materials, see B31.1:2006 paragraph 131.4.2 where preheat for P-1 is listed as 175 deg F if the two conditions of .3% max specified C and >1" thickness are met; If you are working on process pipe, B31.3:2004, then you probably have absolutely no argument and you can't win, see Table 330.1.1 where P-1 preheat are only listed as "Recomended".
The story will likely be different for the low alloy's you are talking about and if you are joing P-1 to low alloys then the required B31.3 or the B31.1 preheats for the low alloy in question will govern.
Ironically, I have had to qualify a couple of new WPS's and used no preheat and no stress relief which have passed tensiles and bends. And it makes you wonder why bother! (I hope and presume the story would be different if Charpy's were involved). (edit: I said "no" preheat but should have said "70 deg F" which was room temp at the time.)
What you DO have to do is follow your qualified WPS, or else qualify another WPS w/o preheat.
Tom,
If you qualified a WPS without preheat would it not be ineligible for work in accordance with B31.1 even though bends, tensiles etc were fine ?
I have only ever used chromolly on power piping, is there other applications for it which would allow say B31.3 to be used and therefore no preheat requirements ?
Regards,
Shane
Hi Shane-
Regarding no preheat on NDTIII's post for P-1 mat'l, the way I read it is that unless the two B31.1 conditions are met, i.e., specifyed C > .3% and thickness > 1-inch then preheat is not required. This is for P-1 only. Chrome-molys will be different and the listed preheats are mandatory.
I believe that a qualified WPS w/o preheat may trump spec requirements IF reviewed AND approved by the engineer of record. The preamble in the ASME documents usually address this situation, B31.1 does. I have not seen this situation arise in a B31.1 application. My comment regarding qualifying a WPS w/o preheat was in the use of 4130 & 4340 alloys for some Mil Spec applications and in those couple of situations the engineers were in the review/approval loop. The point of my comment was to remark on my own surprise that eliminating pre & post heats still produced acceptable test results.
The simple answer is yes, it is important. The very reason that code bodies insist upon preheating for the applications you listed is that there is a mountain of data (and I mean Everest here) that supports the metallurgy that a minimum preheat requirement is essential for ensuriong that delayed cracking and microstructures with improved toughness (depending upon the alloy of course) will result.
If you have engineers that are arguing that it isn't necessary I would think that it would be incumbant upon them to supply evidence and data to support their contrary view. Otherwise go with the wisdom here.
JS55-
To some engineers, the PQR data is all the evidence they need to support their contrary view point and that may be a hard point to argue especially since (presumably!!) they will have intimate knowledge of their application and operating environment. Fortunately, most engineers that I cross paths with accept the Codes and standards and will "go with the wisdom".
Tom,
There are certainly, as indicated in other posts, variables that can mitigate the need for PWHT. Material thickness, alloy content or type, welding practices, joint design, etc., and engineering can certainly be utilized to take advantage of these variables.
And I myself have argued for engineering perogative as well instead of the usual knee jerk logic.
But I would hope they would carry more than a single PQR into court with them in the face of mountains of metallurgical and engineering data (especially with CrMo's) to the contrary in case of a failure.
How else is one to drive the moisture out of the steel?
It explains why I can't keep a can of beer in the refrigerator! The darn liquid leaks out through all those pores in the metal! :(
Al :(
Al,
I really think there is another explanation as to why you can't keep a can of beer in your frig.
I know, thats your story and your stickin to it.
My kids get to it before I do?
Al :)
One of My friends is starting to have that problem with His 10 year old. He can't set a beer down and get back to whatever He was doing without the kid drinking it when He isn't looking. Because of this, He is having to cut back on His own drinking, maybee not an all together bad thing...
true story - a troop of VIP engineering managers were touring our facility last year and came though the weld shop. After a brief show and tell, one asked how we know what temperature to heat the metal to before welding, which I thought was a good question coming from a management type. I told him that we need to raise the temperature above the dew point of the particular alloy depending on the barometric pressure of the day, but since we don't always know what that is we usually go with 400 degrees. I got some very serious head nods and they all moved on.
Tom,
A better answer would have been "I check the WPS and make sure the preheat is in accordance with the WPS requirement". 400 degrees for a SS would be a bit over the edge.
Regards
Fred-
I think you missed the point, I was just having some fun at the expense of the suits.
And I was chiming in with Al's beer can joke, which crosses over to many other discussions in the last year about phereat and hydrogen control.
It's the old "if you don't know the answer, baffle them with bullXhit!"
Al
If you are constructing to B31.3 then, para 330.1.1 applies. Otherwise stated in the Owner's requirement.
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