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Up Topic American Welding Society Services / Technical Standards & Publications / Minimum preheat & interpass temperature part 2
- - By S. WINAI (**) Date 09-07-2012 09:24
Let's say if  do a procedure FCAW  Process qualification on a 1"(25 mm) plate grade EH 36 and preheat and minimum interpass temperature record is 65 Degree C.
So can write in WPS minimum preheat and interpass temperature according to AWS table 3.2  for plate thickness 1/8”(3mm) to unlimited.( 1/8” to 3/4” 0 C, over 3/4” to 1-1/2” 10 C, over 1-1/2”  to 2-1/2” 65 C,over 2-1/2" 110 C.)

Thanks

winai
Parent - - By jwright650 (*****) Date 09-07-2012 11:19
FCAW is considered a low-hydrogen process, so if the plate material is ASTM A131 EH 36, it will fall into category B(notice the welding processes listed. ASTM A36 is in category A and B, but the welding process used determines whether it falls into A or B. Typically low-hydrogen electrodes require less preheat in the material than non-lowhydrogen electrodes.

Don't forget to look at the subscripts, 1/8"-3/4" has an "a" by the temperature(so Note "a" applies)

"Note a: When the base metal temperature is below 32°F[0°C], the base metal shall be preheated to a minimum of 70°F[20°C] and the minimum interpass temperature  shall be maintained during welding."
Parent - - By Shane Feder (****) Date 09-07-2012 13:22
John,
The tables listed by K.Winai are for pre-qualified materials.
The impression I got was he had qualified a PQR with a 65 degree celcius preheat.
If that was the case would he not be governed by Table 4.5 and minimum preheat on the WPS would be 50 degrees (-15 degrees max as per essential variables)
Or am I missing something ?,
Cheers,
Shane
Parent - - By jwright650 (*****) Date 09-07-2012 14:12 Edited 09-07-2012 14:16
Shane you are right...I missed the fact that he was using a "qualified WPS"(good eye).
In using Table 4.5 you are correct about item #35 for any decrease in preheat of more than 25°F[15°C], take note that there is an allowance for reduced preheat during production given by Note "d" in Table 4.5, as long as it complies with Clause 5.6.

EDIT:
I'm wondering why they would use a preheat higher than necessary for 1" thick material to start with, because it ties them down to using more preheat than is really necessary on the WPS. For 1" they could have used 50°F[10°C] instead of 65°C.
Parent - - By S. WINAI (**) Date 09-08-2012 03:32 Edited 09-08-2012 05:57
Table 4.5 item 35,36 (d) The production welding preheat or interpass temperature maybe less then the PQR preheat or interpass temperature provieded that the provisions of 5.6 are met. and the base metal temperature shell not be less than the WPS temperature at the time of subsequent welding.
   5.6 Preheat and interpass Temperatures. Base metal shall be preheated, if required, to a temperature not less than the minimum value listed on the WPS( see 3.5 for prequalified  WPS limitations and Table 4.5 for qualified WPS essential variable limitations). My understanding is only prequalifiend WPS can use minimum preheat state in Table 3.2. If qualified by procedure test then use Table 4.5 minimum decrease allow 15 degree C. PQR record 65 degree C. so minimum preheat temperature should be 50 degree C  for plate 1” thick.But how if plate thickness less than 1” thick ? Let said if plate 1/8”( 3mm) thick. it necessary that minimum preheat must be 50 degree C?
Pls help if I miss understanding.

  Thanks & regard,

   winai
Parent - - By Shane Feder (****) Date 09-10-2012 11:28
K.Winai,
Why did you preheat the PQR to 65 degrees celcius ?
Ambient temperatures in Thailand are about 30 degrees celcius average so if your base material temp was 30 degrees you record that on the PQR.
You didn't need any preheat based on AWS D1.1 material thickness requirements.
Then your WPS will read - No preheat required if ambient temp is greater than 15 degrees celcius.
Mai mee punhaa !,
Cheers,
Shane
Parent - - By S. WINAI (**) Date 09-10-2012 13:03
Hi, koon Shane.
kop koon krap!

Because when they do the test they make it sure to pass, they need to preheat to 65 degree C.so that they dont waste the money if PQR failed. when the time to go  production welding,this preheat can make trouble some. slow down productivity cause of preheat requirements.

mee punhaa mak mak krap!

best regards,

winai
Parent - - By Shane Feder (****) Date 09-10-2012 13:30
Chai khrap - punhaa mak mak !
Yes, you have a very big problem.

This procedure will require minimum 50 degrees celcius on all thicknesses covered by this WPS (6 mm ?)
Why if it is an AWS D1.1 recognised material did you not use a pre-qualified WPS ?
Only reason you should be qualifying PQRs to AWS D1.1 is if the steel you are using is not recognised by AWS D1.1.
No need to run a PQR !
Write a WPS based on electrode manufacturers requirements and list preheat temperatures you have quoted above and you are good to go.

As I said - mai mee punhaa !
Send me an e-mail at sbrwelding@hotmail.com if you need more help,
Cheers,
Shane
Parent - - By eekpod (****) Date 09-11-2012 10:17
maybe the joint wasn't pre-qualified? just wondering
Parent - - By S. WINAI (**) Date 09-11-2012 14:23
hi eekpod,

the joint is the same as prequalified,but some part of the structure is CVN requirements and also some part need to do welding with ceramic backing.thats why i think  they need to do PQR test because of this requirements and this is my idea, but what QA do.i dont know because i sent only welder to do it there.

thanks,

winai
Parent - By eekpod (****) Date 09-12-2012 10:28
ok, because you had to use ceramic backing you had to perform a PQR to qualify the WPS, I get it now.
Up Topic American Welding Society Services / Technical Standards & Publications / Minimum preheat & interpass temperature part 2

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