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Up Topic Welding Industry / Technical Discussions / Preheat or no preheat!
- - By RButler (*) Date 12-06-2007 14:25
I am doing procedure qualifications on 516Gr 70 Plates for an up coming job using ER80S-Ni1 filler metal. I am using  the GMAW process and 99/1 argon oxygen for gas coverage. I have not seen any information that says I should preheatbefore welding. My question Is: should I preheat before welding, andf if so waht would be an approperiate temperature for preheat? Interpass temperature also is a concern to me . What should the interpass maxium temperature be held to during the welding cycle?

Ron B
Parent - - By 803056 (*****) Date 12-06-2007 14:48
There are many reference documents that can be used to determine the required preheat needed to prevent cracking.

If you are not welding in accordance with a specific welding standard such as ASME, AWS, or a military welding standard, I suggest you look at one of the electrode manufacturer's web sites to see what they have to offer in the way of recommendations or texts on welding. One that I like is the Lincoln "Welding Procedure Handbook".

I would also suggest that you consider adopting a nationally recognized welding standard for your "shop practices". If you are welding miscellaneous steel and doing repairs on machinery, I would recommend purchasing a copy of AWS D1.1 and use it as the basis of your shop practices. If you weld pipe, then consider an ASME piping code such as ASME B31.3 for process piping. If you need a "how to" standard, then stick with AWS standards. AWS will provide more information on how to make an acceptable weld than ASME standards. AWS will provide information on matching filler metals to be used to weld different base metals, electrode storage, preheat requirements, joint details, etc.

The draw back for the small operator is the cost of purchasing the documents from either AWS or ASME, but consider them as a cost of doing business. Consider buying an older edition of AWS D1.1 from Amazon or EBay to save a few bucks. Any version of AWS D1.1 is better than none, but try to get a 2000 version or later edition.

Best regards - Al
Parent - By js55 (*****) Date 12-06-2007 15:12
RButler,
Advice really doesn't get any better than the above post. You're just gonna have to bite the bullit and get at least a couple of the docs Al suggested. Especially considering that becasue you are using Ni steel filler you are probably dealing with a reasonably critical application (low temp impact stuff). The good news is 516 is a terrific material. Very tough, fine grained. If I had to guess I would say someone's done some research already matching Ni steel filler with 516.
Good start.
Parent - By toddler (**) Date 12-21-2007 11:30
I don't know if this can be of help. Here are some of the PQR's we've done successfully:

               
  Process  Mat'l Thk  Fillermet  Preheat  Interpass  PWHT  IMPACT 
  FCAW  38mm  E71T-1  10°C  ---  none  no 
  SMAW  37mm  E7018-1  100°C  250°C  none  no 
  FCAW  25.4mm  E71T-1   27°C  490°C  yes  no 
  GT/SM  28mm  70S/7018-1  100°C  250°C  yes  -60°C 
  SMAW  41.8mm  E7018-1  150°C  150°C  yes  -29°C 
               
Sorry nothing for GMAW. Depending on the service application, you may treat this as an ordinary carbon steel and use E7018 (but qualify a procedure).
Parent - - By jon20013 (*****) Date 12-21-2007 12:02
The gents give you some great insight.  You don't mention material thickness nor application so it's extra difficult to give you specific information and not wanted to "spoon feed" anyone all I can say of it were in my shop, I normally specify preheat, but of course, the temperature that varies with thickness and alloy.  Using just a very, very general guideline, I'd say preheat to 150F and hold your interpass to 450F or less, if possible.  Now, theres a little more good advice, do some homework!
Parent - - By darren (***) Date 12-22-2007 18:49 Edited 12-22-2007 20:55
i cant imagine where 150 200 to start and 450 max interpass is bad advice for any steel as a baseline. if you were to accomplish that alone as a standard the whole industry would be providing a better product in general.
Parent - - By john baxter (*) Date 12-30-2007 07:56
This is a bit of concern. The grade of steel you mention is pressure vessel material for moderate and low temperature service. Do you not have a Welding Engineer to develop a pWPS? You need to know service conditions, chemistry of the material and thickness for a starter. If you do not know this then you are onto plums.
Parent - By js55 (*****) Date 12-31-2007 14:52
If I may, if you are using Ni fillers you clearly are working to a cold temp application and so you need to minimize your preheat as much as possible.
SA-516 is a fine grained material with really good low temp toughness and any heat added to it will decrease the cooling rate and create an HAZ with lesser properties than the UBM (unnaffected base material).
Even achieving what is essentially a normalized (though with contact cooling) microstructure, with welding, (keep in mind this stuff is usually delivered normalized or N & T), your HAZ will not achieve the toughness of the UBM. So, if you're in a regime cold enough to require BM charpies keep the cooling rate as quick as possible.
Up Topic Welding Industry / Technical Discussions / Preheat or no preheat!

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