I am working in a pressure vessel manufacturing company. I told my boss we need to preheat some of the materials before welding. I showed all calculations, and standards but I never saw any standard that says preheating is must or just an advice. All standards I read says guidance. Could you please tell me is preheating is a must?
Redrua,
WELCOME TO THE AWS WELDING FORUM!!
That will depend upon many factors. You have told us you are working to ASME, but how about material grade, thickness, process, ambient temps. You said it is in a shop environment, it may well be that no pre-heat is required. But it is hard to give you any sound direction without more information.
Have a Great Day, Brent
Just to go a little further of what Brent said, ASME VIII (there are three Divisions, Division 1 being the most used), states when and how to perform preheating, interpass temperature maintenance and post weld heat treatment.
They depend, as Brent said, from the chemical composition of the base material, its thickness, process etc. Without that information it's impossible to give you any advice.
Another design and construction standard is AD Merkblatter, used in Germany and other European countries. To be frank, I'm not familiar with it.
Giovanni S. Crisi
Sao Paulo - Brazil
What does your WPS state?
preheat to remove moisture!
redrua,
It would depend mostly on what the code of construction is you are building to. e.g ASME Sec. VIII DIV I, II, or something else? Do you know that information? Secondly, do you have a WPS (welding procedure specification)? If so, what does it say for pre-heat?
Thanks
Jim
Hi redrua
Had another look at your post, and see that you appear to be talking only about pressure vessel codes. I will answer in terms of the ASME PV codes.
There are numerous circumstances within the different Divisions of ASME VIII where pre-heat is a requirement. (e.g. when performing repair welds following PWHT; when performing welding to UHT vessels; as an alternative to PWHT under certain circumstances etc.) In terms of "blanket" pre-heat requirements, such as found in B31.3, ASME VIII takes a different approach. Instead of giving a table, and making it mandatory, the information is given as guidance, but the onus is placed on the fabricator to prove that whatever welding procedure he qualifies, that the need (or lack of need) for pre-heat is qualified there. Given that there are more different variables that can influence the need for pre-heat when making vessels than when making piping, it is more difficult to be dogmatic about the actual pre-heats. Also, in critical applications there would be a need for producing production test plates etc. which would potentially highlight any "dodgy" welding practices. So, it would be possible to perform certain welds without pre-heat, but the resulting welding procedure will either not pass the required tests, or they will "scrape through", but will not be robust, resulting in problems such as hydrogen cracking on the job, or the production test plates not passing the required tests.
So, while it may be possible from a code perspective to dispense with pre-heat under many circumstances, it increases the risk of the product not meeting other code requirements, and will therefore result in greater costs associated with failures, than just following the "good engineering practice" pre-heat guidance.
Hope this helps.
Regards
Niekie
"If we do not know what we do not know, then how will we be able to come to the conclusion that we do not know? Forums like this help us with the process. I have certainly been helped in this way on this very forum!"
THAT has to be the awesomest summation!
And so true for me.
Thanks for this jewel of wisdom.
John
I think I couldn't explain what I want to tell.
We have WPS and PQR's for the weldings because the Codes (ASME, EN or CODAP) says weldings should do according to a WPS and PQR. I am the one preparing the WPS and PQR's. I am calculating the preheat temperatures according the chemical analysis of the steel. I do not have problem about calculations.
My problem is whenI tell my boss we should do preheating to the material because of the ambient conditions and material condition my boss refuse it. He tells that no standard says preheating is a must. He do not want to do it because preheating cost money to him. I need to show him a standard that says if preheating is needed according to conditions we have to do it without questioning it but all codes I read says preheat temperature is guidance. If I can't show, he will cancel all preheating procedures.
Redrua,
Did you qualify the PQRs with preheat ?
If so the requirement for preheat is based on your PQR.
If no preheat used in the PQR (if you are in Asia a lot of the ambient temperatures mean you do not require preheat) then you do not require preheat for your production welding.
ASME VIII Div 1 (surprisingly) does not have any requirements for preheat - only recommendations.
I thought B31.3 and B31.1 might give some requirements but B31.3 only has recommendations (for basic P1 material) and B31.1 only required with a specific CEV and a specific thickness (again for basic P1 materials).
You also mention EN and CODAP codes - you need to be more specific as the EN codes can be a lot more stringent than the ASME codes.
Regards,
Shane
redrua,
further to Shane's valuable advice/explanation.
If you are referring to EN you can quickly eliminate your boss' questionable behaviour.
Look at EN 1011-2:2001 (Welding — Recommendations for welding of metallic materials — Part 2: Arc welding of ferritic steels), pp. 36-38.
Actually however, your boss should have a thorough read beginning at 'page 8' already, firstly mentioning 'Preheating' as well as 'page 33' of this standard.
Here the specification explicitly deals with "Method B for the avoidance of hydrogen cracking in non-alloyed, fine grained and low alloy steels".
Page 39 (C.3.6) moreover covers some considerations on "Welding without Preheating".
I suppose, you can put your mind at rest again after your superior had a look into all this. Certainly that will both open his eyes and will recompense you for your efforts/patience.
EDIT: The big file size prevents from upload. However, you can find a free version at:
[deleted links to copywrited material - moderator]
Hope that helps you.
Electrode,
Thank you for your additional EN info but again it is only "recommendations".
I think we would all be in complete agreement that preheat on heavy wall thicknesses (as usually found in pressure vessels) is definitely beneficial but I am struggling to find any actual "requirement" ?
Cheers,
Shane
Shane,
thanks!
Yes, of course you're right and I fully agree.
'Funny' actually, that even nowadays there's still need obviously for even discussing this.
Some of the forum sections dealing with similar questions are packed with meaningful advice from outstanding and experienced individuals - including yourself.
Additionally I would recommend 'redrua' to get in touch with the steel producer/supplier. Usually that can help as well in case of doubt.
When a condition is mandatory, you must follow it whether you like it or not.
When a condition is recommended, it is recommended because there are good reasons to follow it. In my opinion, if you don't want to follow it, you should have better reasons than those which were used to make the recommendation. Does redrua's boss have those reasons?
This is the argument redrua may use to convince his boss.
Giovanni S. Crisi
By 803056 
Date 03-25-2013 01:30
Edited 03-25-2013 20:20
I have to support your boss' position here.
The boss may not be right, but he is never wrong.
Ask your boss if he is in agreement that preheat should be sufficient to drive the moisture out of the pores in the steel. If he agrees that the steel should be heated to ensure the steel is moisture free, find another job. The company is going to go broke shortly because there is an idiot at the helm.
OK, enough of the sarcasm, preheat is used the ensure an excessive cooling rate does not result in undesirable microstructure. Whether an undesirable microstructure will result is a function of the total chemistry of the alloy, thickness, ambient temperature, and heat input. Add a degree of restraint, toss in some diffusible hydrogen and you may have created the perfect conditions to cause delayed cold cracking. There is always the chance the stars will be in the proper alignment to avoid cracking. Call me a "Nervous Nelly", but I do everything in my power to avoid such complication.
Different welding standards have different recommendations and different requirements regarding the need for preheat and how much preheat is necessary. The benefits of preheat when welding carbon and high strength low alloy steels are widely recognized. The preheat temperatures listed by most welding standards are typically considered to be minimum preheat temperatures.
Since you mentioned pressure vessels and you also referenced ASME, you are required to qualify the WPS in accordance with ASME B&PV Code Section IX. You are then locked into the temperature range permitted by Section IX based on the preheat temperature used when you qualified the WPS. The actual preheat used must be recorded on the PQR. If post weld heat treatment was used, it too must be addressed by both the PQR and WPS. Be forewarned that the construction code, i.e., Section I, Section VIIII, B31.3, etc. have the nasty habit of modifying or adding to the requirement of Section IX. It complicates matters, but if you are aware of the construction code, it simply adds a level of detail you need to address.
Make sure your WPS provides the welders with specific information about the weld joint details you want them to use. Simply stating "all fillets and grooves" provides them with about the same level of information as your boss telling you to go design something without telling you what he wants. If you want the groove details to comply with B16.25, show them a sketch of the groove preparation. If you want the slip-on flange to be welded around the hub as well as around the circumference of the end of the pipe and the inside of the slip-on flange, indicate that is what you want with a sketch and specify the weld sizes of the fillet welds. Your welders may have no access to the applicable welding code or more likely, they have never seen a copy of the code, so it is up to you to provide them with the information they need.
Best regards - Al
redrua
preheat is mandatory according to its thickness,material type. if u provide more info then i can specify the importance of preheat.
you can refer asme sec viii for preheat details ....
Hi Vignesh,
kindly! help and share, preheat is mandatory for material FH 36 and thickness is 1"( 25.4 mm). ambient temperature 30 degree C.
Thanks,
Winai
WINAI
can u specify its p no, uns no or spec no......it will b more helpful
redrua,
reading this thread through its end, to me, the confusion seems greater than with its beginning.
I was almost certain to understand codes and standards just as some 'least common denominators', agreed between, sometimes, most different advocacy groups.
But, at the end of the day it truly seems that every code and standard must be considered a 'recommendation' only.
Hence, based upon your (good) initial post, it is truly your boss who seems to be right.
At least as long as he is literally willing to take the risk of standing legally "corrected" in case of some - perish the thought - disaster.
Hi redrua
I am not sure that I agree that pre-heat is not a requirement. There has been a change in the pre-heat approach of ASME B31.3 in the 2012 Version, which states the following:
330.1.1 Requirements. Unless specified otherwise
in the engineering design, the minimum preheat temper-
atures for materials of various P-Numbers are given in
Table 330.1.1. The thickness intended in Table 330.1.1 is
that of the thicker component measured at the joint.
This means that if ASME B31.3 (2012 version) is the design and fabrication code, and there is no other guidance in the design documents, (e.g. drawings or client specifications) then you need to follow the minimum requirements given in the referenced table.
Hope that helps.
Regards
Niekie
While many of the codes, specifications, and standards are 'suggestions' they become 'requirements' when they are the specified controlling documents according to either the Contract Documents and/or Government Regulations.
I am currently on a D1.1/1.8 project (yes, I realize I am comparing oranges with apples) where the Contract Documents state that in all cases the fabricator will use enough pre-heat to remove moisture before welding. Thus, regardless of the Code requirements there will be at least a minimal amount of pre-heat applied before any welding to ensure the absence of conditions which would cause condensation to develop at the weld joint. So check your General Notes, Job Specifications, and any other part of Contract Documents for wording that may dictate pre-heat.
Wording of a complete Clause often needs to be evaluated because it is not that pre-heat is 'recommended'/'suggested' but the wording is referring to it being a 'minimum' factor. They are not allowing that it NOT be done, they are allowing that it can be even higher than the 'recommended' amount.
I have probably done nothing to clarify this issue, just some thoughts that hopefully apply.
Have a Great Day, Brent
