API5L X65 PSL2 + PWHT 2

[gabstag]

I am buying API 5L X65 PSL2 plates 39mm thk. We asked for normalized plates but the mill says that this cannot be possible becouse the plates sour resistance will be lost with the normalizing temperature (about 600°C).
They propose TMCP plates without possibility of PWHT.

I need the plates for welded pipes according B31.3 and I need to perform two PWHT's at 593-605°C (one during the pipe fabrication and one during the site erection.

How do you think I have to procede?

Thank you for your co-operation

 

[metengr]

If you intend to use the plates to fabricate seam welded pipe in accordance with ASME B31.3, you will need to perform PWHT, and in this case my preference would be a normalize and temper post weld heat treatment versus a sub critical PWHT.

The proposed alternative by the mill is actually plate specified to ASME SA 841 - "Standard Specification for Steel Plates for Pressure Vessels, produced by Thermo-mechanical Control Process (TMCP)". I would recommend you review this specification because it requires mention of PWHT requirements in the purchase order to the mill because test coupons must be produced to simulate post forming or PWHT conditions to assure properties are not degraded. The maximum specified PWHT temperature for TMCP plate is 1200 deg F.

If the mill is proposing to substitute the TMCP plate to avoid PWHT, this is not a correct assumption for your application. The PWHT will need to be performed for plate thickness in excess of 3/4" (19mm) in accordance with ASME B31.3 for S-No 1 material (API 5L X65).

I would proceed with using API 5L X65 material and after welding perform a normalize and temper post weld heat treatment.

 

[metengr]

One additional note; for butt welds in the field, this of course would be a sub critical PWHT that must be performed below the tempering temperature of the normalize and temper PWHT that is performed during fabrication of pipe spools in the shop.

 

[gabstag]

Than you for your reply.

I would like to clarify our position.

We have to manufacture welded pipes for sour service starting from plates API5l X65. They are 48" and 39mm thk.
The client specification requires as design code ASME B31.3.

Now, the steel mill can supply TMCP plates only. They state that normalized or Q&T plates loose the HIC resistance due to the high temperature of normalizing process.
They state that with TMCP plates the PWHT is not necessary or if it is mandatory the max T must be 560°C for 2min*mm.

This is a deviation to ASME 31.3.

And what happen after the second PWHT on site?

 

[metengr]

Quench and temper heat treatment will improve resistance to HIC and increase toughness. You can use an alternative plate like SA-516 Grade 65, roll form, seam weld and quench and temper to enhance HIC resistance during fabrication.

Applying a second PWHT in the field for butt welds will affect toughness and HIC resistance of the plate. However, the mill can evaluate for the second PWHT application and perform an HIC test to assure minimum properties using test coupons. This has to be discussed and agreed upon with the mill.

 

[gabstag]

The steel mill states that the Q&T plate according API5L X65 doesn't exist.

 

[metengr]

API 5L is a Specification for either seamless or welded pipe from 1/8" up to 26 NPS, not plate.

What exactly are you trying to do? Are you intending to fabricate pipe to API 5L?

 

[gabstag]

Yes, I intended the pipe API 5L X65 but the steel mill said that the plates for this welded pipe for sour service can be supplied in TMCP only and Q&T one don't exist.

What I have to do to have 2 PWHT's according B31.3?

Do you think the only way is to change material?

 

[metengr]

Yes, I would use ASME SA-516 Grade 70 plate to fabricate your 48" diameter pipe under ASME B31.3. This plate material can be made to order for increased HIC resistance by specific control regarding chemical composition (reduced sulfur content and inclusion shape control).

The plate could be supplied after welding into pipe in the quenched and tempered or normalized and tempered heat treatment condition for maximum HIC resistance. The mill can work with you regarding test coupons to evaluate HIC after field PWHT.

 

[gabstag]

Thank you

I will try this way, but the pipe thikness will increase with this material.

 

[stanweld]

With regard to B31.3, please note 331.2.2 Exceptions to Basic Requirements.
(a) "When provisions less stringent than those in para. 331 are specified, the designer must demonstrate to the owner's satisfaction the adequacy of those provisions by..."

Whereas you are the pipe manufacturer, the resposibility to demonstrate that your pipe meets API 5LX65 requirements and (Engineering)HIC requirements after manufacturing including PWHT rests with you - not the skelp manufacturer. It appears that you have no justification at this time to provide pipe meeting the Engineering requirements without additional research and testing.

Has the Owner or its Engineer specified the purchase of X65 pipe for the application?

 

[gabstag]

The X65 has been specified by the Owner.
I am not the pipe manufacturer, I am a package integrator.

I know the exceptions to basic requiremente 331.2.2, and I asked to pipe mill and steel mill to demonstrate the adequacy of the proposed material but up to now they didn't answer and it seems they don't want answer.

 

[stanweld]

It appears that the pipe mill cannot provide X65 pipe that can meet the Owner's requirements. If you hve sourced from other reputable mills and they have provided the same response, it is quite possible that the Owner's requirements cannot be met. I know that when I was highly involved with these materials about 15 years ago, no mill could meet the requirements that you describe for X65 with the heavy wall thickness defined. Lower strength steels were required to meet the HIC (wet H2S) cracking resistance requirements.

As metengr stated, skelp from SA-516 normalized may be required, which of course will greatly increase the wall thickness required of the pipe. A specially fabricated lower strength (X42 thru X52) pipe may also be available.

 

[gabstag]

Yes, I confirm that this is the present situation.

The Owner can accept the code deviations about the PWHT, but requires further information as indicated in B31.3, 331.2.2 Exceptions to Basic Requirements, as i.e.:

- thermal cycling
- flexibility stress levels
- probability of brittle fracture
- additional PQR testing

Steel and pipe mills do not provide any detail and at the moment I am in big trouble with my Client.

 

[stanweld]

Appropriate engineering analysis can resolve the first three items. If brittle fracture is to be considered at the design conditions or required by B31.3, impact testing of pipe and welding procedures can be specified and then reviewed with the pipe manufacturer. I would assume that additional PQRs will be required to be performed by the pipe manufacturer and installer to confirm strength and ductility and appropriate hardness to meet NACE MR-0175 or equivalent requirements.

 

[gabstag]

But what doyou think? With this material the PWHT is mandatory or not (as states the steel mill)?

 

[metengr]

gabstag;
Why don't you obtain some of this material from the mill and evaluate the effects of PWHT and perform HIC resistance tests? This information will provide the necessary engineering information to review with your client. All we can do is speculate and this will serve no purpose.

 

[stanweld]

Whereas API 5L is a listed material in B31.3, Appendix A and the longitudinal weld is not required to be post weld heat treated under the material specification for X65 which is also listed in Table A-1, the pipe is not subject to PWHT as defined in Chapter V of B31.3(ref. Section 327). PWHT per Section 331 is required for the welds involved in fabrication (ref Section 300.2), assembly, and erection, unless waived by the Owner per 331.2.2.

 

[gabstag]

stanweld
could you please explain better where in B31.3 is indicated that the PWHT after the longitudinal weld is not required?
And what about the PWHT at 560°C for 2 min*mm (as indicated by the steel miil) for the circunferential welds during the assembly and erection.

Thank you

 

[stanweld]

The requirements for PWHT per 331 are for fabrication, assembly and erection of pipe systems. Fabrication is defined in 300.2. It does not include manufacture of pipe to a listed material specification.