Post Weld Heat Treatment Times and Cycles (Urgent Help Required) 1

[KnaT]

Hi

This is long case but I will really appreciate your expert opinion on this.

I have was going through a vendor PQR with following details:

Applicable standards: API 6A, NACE MR 0175, ASME IX
Material AISI 4130 Quench Tempered, 75k YS, 38mm thick
Process: SMAW
Consumable: E7016 (root) E10018 D2 (filling capping)
PWHT: 630 Deg. C for 4 hours 45 minutes

Question: By what temperature can the vendor deviate in their WPS? Vendor has mentioned 630 +- 10 Deg. C. Can it be 630 Deg. C +- 20 Deg. C? I believe as long the temperature is approx 50 deg. below tempering temperature and above 600 deg. C it should be ok. Is that correct?

PQR coupon was 38 mm and it was heat treated for 4 hours 45 minutes. The WPS says PWHT holding time to be 4 hours 45 minutes to 5 hours 55 minutes. I believe it is incorrect. Taking the convention of 1 hour/inch material thickness for holding time. I believe the PQR coupon was required to be post weld heat treated for only 2 hours. The extra 2 hours 45 minutes might be a compensation for the repair welding.

Question: Having said that shouldn't the WPS say holding time to be 1 hour / inch?

The vendor has used the WPS to weld a coupon 3 inch in thickness. The job was then heat treated for 5 hours.
There was a repair in the weld after PWHT which was removed and re-welded.


Question: What should be the holding time for the second post weld heat treatment cycle? Will the final repair welding still be acceptable as per the qualified procedure? If not how can it be qualified? I think the vendor should weld another coupon of 38 mm thickness and post weld heat treat if for 10 hours. Perform tensile test to ensure that the material still has the required tensile properties.

 

[metengr]

Question: By what temperature can the vendor deviate in their WPS? Vendor has mentioned 630 +- 10 Deg. C. Can it be 630 Deg. C +- 20 Deg. C? I believe as long the temperature is approx 50 deg. below tempering temperature and above 600 deg. C it should be ok. Is that correct?

Yes, or if the construction code requires a specific minimum to maximum PWHT temperature range.

Question: Having said that shouldn't the WPS say holding time to be 1 hour / inch?

Was the above qualified with impact testing? The extra time for PWHT is typically for notch toughness properties because notch toughness may degrade over extended PWHT time. This is why I asked about impact testing. Extended PWHT time is normally for repair cycles.

There should have been no repairs made to the weld coupon for procedure qualification. Another coupon, 3" thick must be welded for qualification.

 

[SJones]

API 6A is not overly restrictive when it comes to control of PWHT. However, it does demand that PWHT is within the temperature range as written on the WPS. Then, at PSL 3, it allows a 'nominal temperature range, +/- 14 deg C', which probably should have been "nominal temperature +/- 14 deg C." It does not worry about holding time. This is where one would invoke ISO 17663 if an ISO 3834-2 welding quality operation is required under ISO 9001. ASME IX is clear about the holding time that is qualified by the procedure qualification test.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[KnaT]

Yes, or if the construction code requires a specific minimum to maximum PWHT temperature range.

The construction Code is API 6A which unclear about the PWHT. It just says that manufacturer has to perform the PWHT as per the qualified WPS.

Was the above qualified with impact testing? The extra time for PWHT is typically for notch toughness properties because notch toughness may degrade over extended PWHT time. This is why I asked about impact testing. Extended PWHT time is normally for repair cycles.

Yes, the WPS was qualified with impact testing.

The vendor has used the WPS to weld a coupon 3 inch in thickness. The job was then heat treated for 5 hours.
There was a repair in the weld after PWHT which was removed and re-welded.

My apologies, it was not a coupon. This was a production weld which was repaired by them.

 

[KnaT]

API 6A is not overly restrictive when it comes to control of PWHT. However, it does demand that PWHT is within the temperature range as written on the WPS. Then, at PSL 3, it allows a 'nominal temperature range, +/- 14 deg C', which probably should have been "nominal temperature +/- 14 deg C." It does not worry about holding time. This is where one would invoke ISO 17663 if an ISO 3834-2 welding quality operation is required under ISO 9001. ASME IX is clear about the holding time that is qualified by the procedure qualification test.

API 6A is putting a restriction on deviation from the WPS but it is not putting any restriction on the WPS itself. This will give a little more "flexibility" when more than one welding procedures are involved. I have seen cases where the temperature ranges on two different welding procedures do not coincide with each other and the job has to go for furnace PWHT. That is the reason I want the temperature range on the WPS to be extended.

 

[jbeckhou]

Search for HEMPS 11.100. This document will answer all your questions, its a little outdated but will provide the information your looking for. From reading your post and vendor welding information, seems correct to me. Didn't see a note stating Preheat Temperature or Inner pass temperatures.

Petrotrim Services

http://www.petrotrim.com

 

[cloa]

http://www.readbag.com/sections-asme-nwhss-pwht-hemps-11-100-a1

Here's one of the web references that can actually link e.g. ASME lists it but download fails.

 

[KnaT]

Thanks Cloa. You are right, it only allows you to read it online.

Jabeckhou: Could you please send us a pdf of this specification? I will really appreciate that.

 

[jbeckhou]

see below link

Petrotrim Services
www.petrotrim.com

 

[KnaT]

Thanks Jbeckhou. It is very informative and has clarified a few of my concerns but now I am feeling that none of my vendor's procedures are qualifying these requirements.

If you use the 1 hour per inch convention, a standard spacer spool will only require around 1.5 hour PWHT soak time. Making it go through 2.5 extra hours of PWHT has a very big cost and time impact on the process. Don't you think 4 hours soaking time for upto 5 inch thickness is a over generalization for simpler, more uniform shapes?

One more thing, do you know of any similar specification for overlay welding as well? I want to know what thickness will they consider for determining the PWHT Soaking Times.

 

[pradipgoswami]

Applicable standards: API 6A, NACE MR 0175, ASME IX
Material AISI 4130 Quench Tempered, 75k YS, 38mm thick
Process: SMAW
Consumable: E7016 (root) E10018 D2 (filling capping)
PWHT: 630 Deg. C for 4 hours 45 minutes

Question: By what temperature can the vendor deviate in their WPS? Vendor has mentioned 630 +- 10 Deg. C. Can it be 630 Deg. C +- 20 Deg. C? I believe as long the temperature is approx 50 deg. below tempering temperature and above 600 deg. C it should be ok. Is that correct?

Answer:- API 6A-6.3.4.2.1 Heat treatment- PSL-3 Components:-
The post-weld heat treatment of the test weldment shall be in the same temperature range as that specified on the WPS. Allowable range for the post-weld heat treatment on the WPS shall be a nominal temperature range, ± 14 °C(± 25 °F). Deviations within the API 6A specified range are acceptable,not beyond this range.

PQR coupon was 38 mm and it was heat treated for 4 hours 45 minutes. The WPS says PWHT holding time to be 4 hours 45 minutes to 5 hours 55 minutes. I believe it is incorrect. Taking the convention of 1 hour/inch material thickness for holding time. I believe the PQR coupon was required to be post weld heat treated for only 2 hours. The extra 2 hours 45 minutes might be a compensation for the repair welding.

Answer:- ASME Sec IX-QW-407.2 The procedure qualification test shall be subjected to PWHT essentially equivalent to that encountered in the fabrication of production welds, including at least 80% of the aggregate times at temperature(s). The PWHT total time(s) at temperature(s) may be applied in one heating cycle.

Here PQR was quaified with 4 hrs+45 mins(i.e 285 minutes) of soaking time.Hence it qualifies WPS up to approx 6 hrs of PWHT time (Note :-80% of this time is 288 mins)



Question: Having said that shouldn't the WPS say holding time to be 1 hour / inch? The vendor has used the WPS to weld a coupon 3 inch in thickness. The job was then heat treated for 5 hours. There was a repair in the weld after PWHT which was removed and re-welded.

Answers:- 1 Hr/inch is the nominal soaking time recommended by ASME BPV codes. However a PQR may be qualified with a longer duration of PWHT time, in order to accomodate further PWHT follwing any weld repair. By ASME Sec VIII, DIV-1,PWHT logic(which is most commonly applied in Non ASME fabrications also) a 4130 (Equivalent Sec IX, P No 4) weld of 3" thickness would require nominal soaking time of 3 hrs max. 5 Hrs is over killed for this thickness.

Question: What should be the holding time for the second post weld heat treatment cycle? Will the final repair welding still be acceptable as per the qualified procedure? If not how can it be qualified? I think the vendor should weld another coupon of 38 mm thickness and post weld heat treat if for 10 hours. Perform tensile test to ensure that the material still has the required tensile properties.

Answer:- If the design requirements calls for a minimum of 5 hrs PWHT soaking following welding, vendor needs to qualify a PQR with 10 hrs of PWHT soak time to accomodate any weld repair and subsequent PWHT. However for a Q&T component the following requires to be enforced:-
-PWHT temperature should not exceed the tempering temperature
- the total PWHT time should not exceed the tempering time
-For critical services,it would be advisable to get a prior basemetal simulation test done at the mill.


Thanks
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299