PWHT

Date 11-16-2011 14:26

Hi vdao3004

If you have qualified 1" material, then you are qualified to 2" thickness, none-the-less, I understand the question. To overcome this requirement, you need to apply the maximum time that you want to use in production. Some client specs require you to qualify at the maximum and minimum time. This maximum time may include additional cycles for potential repairs during fabrication, and for "future maintenance repairs". If you really "go over the top" and qualify a long time, your tensiles and possibly impact tests may fail, so you need to considder carefully for what you will really be using this PQR in the future, and not test for "nice to have" situations you may never need.

Regards
Niekie

By vdao3004 (**)

Date 11-17-2011 00:03

Thanks for response, I just to make it clear per your comment, I must have 2 test plates, 1 is PWHT at 1 hours and 2 plate is PWHT to 2 hours or up to 8 hrs, it is depend on our product,, we always thought that per code we welded the .5 thick test plate and PWHT. at .5 , it will qualify upto 8 inches.

By ozniek

Date 11-17-2011 14:25

Hi vdao3004

According to ASME IX, you do NOT need to do two test plates. You only need to do one, with a PWHT of at least 80% of the time that you will be using in production. Thus you may have a longer time on your PQR test piece as what you use in production, but not more than 20% shorter. I mentioned the short time test piece only because this is required in some client specifications. If it is not required in your client specifications, then you only need to perform the long PWHT time on your PQR test piece.

My understanding has always been that if you have qualified your PQR on 1", and used a 1hr holding time, then in production you may not hold the PWHT longer than 75minutes, irrespective of the material thickness. (In essence, you can then only weld 1.25" with that procedure, to still comply with the ASME VIII requirement of 1 hour per inch of thickness.) This is why it is important to decide up front what thickness you will be welding in production, and tailoring your PWHT to suit. (e.g. 1" qualifies 2" production, which requires 2hrs PWHT, according to ASME VIII. If you want to include the posibility to PWHT twice, just in case you need to perform a repair/modification after you have PWHT'ed your vessel, then double that to 4hrs. You will then perform a PWHT of 4hrs on your PQR test plate.)

I just want to check the code interpretations and see if they say anything different. I will let you know tomorrow, if I can get me hands on the ASME IX interpretations at the office.

Just an aside: Only if your test plate exceeds 1.5" thickness, are you qualified up to 8" thickness.

Regards
Niekie

By vdao3004 (**)

Date 11-18-2011 01:31 Edited 11-18-2011 01:55

Nieke

Per your comment :
(In essence, you can then only weld 1.25" with that procedure, to still comply with the ASME VIII requirement of 1 hour per inch of thickness.) Can you tell how do came up with 1.25 allowed , can tell me what table in the COde which can use.
And I already have WPS certified 1", so now if I want to upgrade the PWHT Thickness, can I create new PQR to add on to this WPS.

Thanks for advice.

By ozniek

Date 11-18-2011 10:02

Hi vdao3004

If you have applied 1hr of PWHT to your PQR test plate, and this must be at least 80% of the time you use on the production work, then the maximum time you are allowed to PWHT on the production work can be calculated as follows:

60minutes = 80%; therefore 1 percent = 60/80 = 0.75minutes; therefore 100% = 0.75 x 100 = 75 minutes; which is 1.25hrs

The ASME VIII Div 1 requirement for PWHT holding time is 1 hour per inch of thickness, therefore if you are allowed to use a PWHT time of 1.25hrs, then you are allowed to PWHT a thickness of 1.25" for production work.

Just to add a point of clarification: The holding time for PWHT must not be calculated on the thickest base material, but on the thickest weld. This means that if your thickest weld on a vessel is 1", (Let us say this is the shell thickness.) but your thickest base metal is 4", (Let us say that you have an unwelded nozzle flange that is 4" thick.) the PWHT holding time will be 1hr, based on the biggest weld thickness of 1". The thickest part of the vessel (your flange in this case) will however dictate the heating and cooling rates of the PWHT cycle.

To answer your last question, yes you can, because you are allowed to base your WPS on more than one PQR, but if you are going to use the same thickness material and the other essential variables remain the same, and you perform the same testing, (only applying longer PWHT) then you will probably not actually gain anything by basing the WPS on both PQR's, unless your client specification asks for a minimum and maximum cycle PWHT.

Regards
Niekie

By ozniek

Date 11-18-2011 09:38

Hi vdao3004

I have confirmed the statement I made yesterday regarding the PWHT times. I will attach two code interpretations that illustrate the point. The fist shows that you can not have a longer PWHT in production, even if the material is thicker than your test plate, and the second shows that you may exceed the production PWHT time on your test plate.

Regards
Niekie

By MBSims

Date 11-19-2011 15:01

On the first interpretation in Question 1, the production PWHT time was to be 3.5 hours. To qualify for a 3.5 hour hold time, the PQR hold time has to be at least 80% of that, which is 2.8 hours. That is the reason the answer to both questions was "No", since the PQR only had a 1.5 hour hold time. It is possible to use a PQR to support a longer production hold time as long as the 80% requirement is met.

By vdao3004 (**)

Date 11-19-2011 15:36

MR. Sims,
Please comfirms me for the 3.5 hrs cal as : first 2 inches is 2 hrs, and 3-8 is added 15min. each. is this correct?
and how many time we can re PWHT the part, and if in case we do many rework and the PWHT time is up, what should we do?
and can we normalized and temper if the time it is up ,so we can restart the cycle again.
Thanks

By ozniek

Date 11-19-2011 16:10

Hi MBSims

Yes, I agree with you entirely.

Regards
Niekie

By MBSims

Date 11-20-2011 05:03 Edited 11-20-2011 05:06

For ASME Section VIII, the PWHT time required for P-No. 1 is 1 hr. per inch up to 2" thickness and 15 minutes per each additional inch that is over 2". For 8" nominal thickness, the PWHT time required would be 3.5 hours as you have stated.

QW-407.2 would only apply if impact testing is required, since it is a supplementary essential variable. If it applies, the maximum PWHT time allowed in production is 1.25 times the PWHT time qualified by the PQR (100% / 80% = 1.25). The heat treatment time can be in one or multiple heat treatments, but the total time can not exceed that qualified. If you qualify on 1" plate, then the maximum base metal thickness qualified is 2". If the PQR PWHT time is 1 hr., then the maximum qualified PWHT time is 1.25 hrs., which would not be acceptable for a 2" thick plate welded in production. So if you intend to weld 2" thick plate, the PWHT time for the 1" thick PQR plate would need to be at least 1.6 hrs.

If normalizing and tempering is performed, the welding procedure must be requalified based on QW-407.1 for a heat treatment above the upper transformation temperature (normalizing), followed by a heat treatment below the lower transformation temperature (tempering). You will not be able to restart the cycle again by normalizing and tempering for a impact tested vessel that is already welded without requalifying the welding procedures that were used to fabricate the vessel.

Rather than normalizing and tempering, the typical requalification would be to weld a PQR and subject it to a longer PWHT time. Many vessel fabricators choose to qualify the welding procedures for extended PWHT times in order to allow for the initial fabrication PWHT plus any subsequent PWHT for repairs. A 8 hr. hold time is common, which would qualify for PWHT times up to 10 hrs. total.

By vdao3004 (**)

Date 11-21-2011 01:57

MBSims,

Thanks, do you have any chance in the past if we PWHT 3.5 for 1 thick plate and passed the Charpy test.

By MBSims

Date 11-21-2011 02:15

It should pass Charpy testing with no problem. However, a 1" plate will not qualify for base metal thickness up to 8". So, why not weld a 1.5" thick plate to qualify a wider range of thickness?

By Unnikrishnan Date 11-06-2015 06:49

Dear Sims,

Your Statements " The heat treatment time can be in one or multiple heat treatments" . Does this mean if the heating time is 4 hr we can do it in multiple heat treatment cycle of 1 hr in 4 times??

By Don56

Date 11-12-2015 20:49

Yes