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Up Topic American Welding Society Services / Technical Standards & Publications / Preheat Requirements
- - By stuzhotwire (*) Date 02-23-2009 17:08
I have searched the subject of preheating and could not sufficient comment on this topic so I'll post a new one.  D1.1:08 section 5.6 Preheat / Interpass Temp states to refer to your WPS for minimum preheat requirements.  If our WPS is qualified for CPJ groove max 1" plate which allows unlimited thickness for fillet welds per table 4.2 part 1 foot note (d), when does the preheat come into effect?  Table 3.2 Catagory B for GMAW and 2 1/2" A36 plate requires a minimum preheat of 150 degrees.  Our current WPS has a preheat min. of 50 degrees based on testing at the 1" plate for groove welds.  I'm confused as to why AWS allows "unlimited thickness" for fillets while not holding a minimum preheat requriement.  My question is, do we ignore table 3.2 since that is establishing a wps and not for production?  If a job requires higher plate thickness but using fillet welds, is the engineer responsible to state preheat requirements on the design drawings or our responsibity to follow code in table 3.2?  If I don't have enough information here let me know. 
Thanks for your help in clearing this up.
Stu
Parent - - By hogan (****) Date 02-23-2009 19:15
Try looking at AWS D1.1 (08) 4.7.4
Parent - - By stuzhotwire (*) Date 02-24-2009 12:35
Yes D1.1 4.7.4 is establishing the preheat for qualifying a wps.  I have asked another cwi and he stated the question never arose before.  He didn't believe there were preheating requirements for fillet welds.  The shop believes the wps is sufficient and allows fillet welds on unlimited thickness.  This is based on the information given in my previous post.  If AWS does not pin it down more precisely than I would assume the shop is right.  I dont' see how I can take the 3.2 chart and hold preheat requirements on the shop over and above their wps.  That's is with the understanding they are not out of the perimeters of their wps.  I wish there were a more clear answer on this but maybe I'm over interpreting.  Thanks again.
Parent - By hogan (****) Date 02-24-2009 13:47
This is an essential variable! How is it not pinned down? I'm not going to quote the entire section, but it states that if you don't follow table 3.2 (if you are lower) you need engineer approval.
Parent - - By 803056 (*****) Date 02-25-2009 04:36
I would be somewhat conservative when specifying preheat. It is less expensive to use preheat than it is to excavate and repair cracked welds.

When you qualify a WPS by testing, the maximum thickness is limited to 2T unless the test is performed on plate at least 1 inch thick. The minimum preheat is no less than 25 deg. F below than that used when qualifying.

It amazes me that fabricators and contractors try to eliminate or minimize preheat and then they act surprised when they have cracking problems. 

I am so ever grateful contractor and fabricators don't get any smarter as the years go by. That's what keeps me gainfully employed.

Preheat is based on the thickness of the thicker member being joined. Whether the weld is a groove weld or fillet weld is immaterial. Any CWI that doesn't know that wee piece of information should be flogged. He is most likely one of those individuals that still believes there is water in the pores of the steel and it must be dried out by the preheat. If I had a rubber "I'm STUPID" stamp I would stamp him with bright red ink right on the forehead so everyone could read it.

If you are a CWI and find that last paragraph offensive. GOOD! The rest of us can have a good belly laugh!

Best regards - Al
Parent - By jwright650 (*****) Date 02-25-2009 12:13 Edited 02-25-2009 14:33
<scarastic tone on>Al do you mean to tell me that the water isn't trapped within the pores of the steel and we shouldn't be drying it out with preheat?<sacastic tone off>...Bwhahahaha...where's my red stamp?
Parent - - By hogan (****) Date 02-25-2009 14:31
I recently was in the position of having a fabricator state that they were removing water from the steel with preheat. I suggested that we should make a wager on it. A weeks pay if you could put the steel in a press and get two drops of water out of it.
Parent - By CHGuilford (****) Date 03-17-2009 16:32
BE CAREFUL!  Those beads of sweat from his brow could end up dropping on the steel when you aren't looking.
Parent - - By stuzhotwire (*) Date 02-25-2009 17:10
OK thanks guys.  A light just went off in my head and hopefully it is not illuminating the rubber stamp.  Ha!  But since I'm not a CWI it doesn't apply. 

It appears the key word I was missing was "minimum" preheat.  Our wps minimun is 50 degrees for 1/2" - 1" plate. 

So I'm hearing it doesn't matter if our wps allows unliminted thickness for fillets because we should know the code mandates a minumum preheat on plates such as 2 1/2" of 150 degrees.  That would be our new minimum preheat even though it is not on our wps. 

Furthermore the code specification is based on material grade, thickness and weld process but not weld type.

The kicker was how they qualified a wide range on the essential variables staying compliant with the wps when the heavier plate dropped into the picture.  Everything was fine until a few pieces of thicker plate showed up and my gut told me to investigate. 

If I'm on taget then great.  If not then throw some more at me.  In the meantime I'll hang on to the stamp just in case. :) 
I do appreciate your help.
Stu
Parent - - By jwright650 (*****) Date 02-25-2009 17:42
Hi Stu,
Take for instance a small A572 gr 50 WF shape column with a web of say 5/16" thick and flanges that are 5/8" thick...but has a 3" thick base plate. The 3" thick base plate would govern how much preheat is required. Remember that the thickest part, at the point of welding, governs....in this case a cold 3" thick base plate would be the heat sink that would suck all of the heat from welding out of that root pass and quench the weld metal too quickly. To counter act this, you would add the proper amount of preheat to the base plate to reduce the cooling rate. And this preheat is verified at a minimum distance of 3" from the joint on the thickest part(in this case the base plate) typically using a tempil stick(a temperature melting crayon).

When I write WPSs for other people, I include the preheat temperatures on the WPS itself, but for our people in my shop, I simply write it saying that the preheat is to be in accordance with AWS D1.1 (current edition)Table 3.2. Auditors have challenged me on this practice in the past, but I teach all of our people how to read a WPS and how to use Table 3.2, so I always welcome them to go out and question any welder on my shop floor, if they have any doubts.
Parent - By Bill M (***) Date 02-27-2009 19:09
Geez...everytime I bring it up here.....well, I think the exact quote is:  "jus git 'er  hot enough to "git the water out".
Parent - By Bert70 (*) Date 03-04-2009 10:54
I would recommend a little caution before you grab your whip... consider the following:
2" A572-50 member
welded (fillet or groove) to a
4" thick A913-65 or A710 Grade A member
using E7018MR-H8 (or some other filler metal/process capable of depositing weld metal with a maximum hydrogen content of 8ml/100g...)

Keep in mind it is the "piece/part" with the highest minimum preheat that governs. In the example above it is the thinner member that governs.

Regading "water in the pores" of the steel... the individual's terminology may be poor, but it does not mean that water is not driven off the surface of the steel when it is preheated. Water can condense on the surface of a material as long as there is sufficient difference in temperature to allow the latent heat of vaporization to be transferred from the water molecule. Just because you can not see it with the unaided eye does not mean it is not there.

It is not necessary for someone to be a physicist in order to be a welder (or even an inspector for that matter), but if you are willing to help them understand the reason why we do things, ie; preheat so we can reduce the cool down rate of the joint..., perhaps you will not go through so much red ink. Just food for thought before you break out that stamp too.
- Bert
Parent - - By DAYANARA (**) Date 02-28-2009 16:22
D1.1 is only minimum requirement, I think best is determining minimum preheat by Annex I (remember is mandatory).
You have reviewed both minimum and maximum base metal thickness and determining preheat. The results haven't below of table 3.1.
When D1.1 said 1" - unlimited, you have thought in other essential variables for example Preheat. (See table 4.5 point 35)

Best Regards.

Dayanara
Parent - - By Nanjing Date 03-05-2009 16:03
With regard to preheat requirements I think American codes, take no offence, treat welding as engineering by numbers. In Europe the minimum preheat suggested for avoiding cracking is given by specifications which give you simple charts to follow (BS 5135- now superseded by some Euronorm). Basically the guidance given is that you must consider a number of factors. These are, with regard to joint configuration, the combined thickness, the arc energy of the process/procedure, the diffusible hydrogen content of the specified welding consumable and the chemistry of the materials being joined. Knowing all these variables, all you have to do is select the correct chart for your variables and read off the minimum preheat required. Apart from giving you guidance on deriving minimum preheats it helps in giving an understanding of why preheat is applied and how you can select materials and consumables to avoid cracks.
Parent - By DAYANARA (**) Date 03-05-2009 16:34
Dear Nanjig

I like your standar BS 5135.
Please.

Thank you
Parent - - By hogan (****) Date 03-05-2009 16:34
AWS gives you minimum preheat requirements. This is just a starting point. It is up to the fabricator to have the knowledge needed to evaluate the entire situation and make a quality product. Maybe the American codes recognize this.
Parent - - By Nanjing Date 03-06-2009 14:43
The point I was driving at was in response to stuzhotwire's statement that someone thought there was no requirement for preheat for fillet welds. I think this is the crux of the matter. Why did this person think no preheat was required? He could not find the section in the code book for preheat requirements for fillet welds therefore he decided that there was was no requirement? or did he not understand the concept why preheat is required? Great emphasis is placed on the welding of primary members however I find that one of the biggest problems has always been in the attitude of welding secondary members to primary members, that is "well it is only secondary steel and only a 6mm fillet". How dangerous, do a search on the Alexander Kielland and look at the reason for the catastrohic failure traced to a 6mm fillet weld which caused the death of 123 men in the North Sea back in 1980. OK materials and welding consumables are not the same now as they were then but we still often encounter cracking problems.
Parent - - By hogan (****) Date 03-06-2009 15:04
That is understandable from a welders point of view.
Parent - By Nanjing Date 03-06-2009 16:03
What?
Up Topic American Welding Society Services / Technical Standards & Publications / Preheat Requirements

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