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P91 Welding Consumables & Questions

P91 Welding Consumables & Questions

(OP)
I'm running an ASME IX/VIII-D1 PQR for a client on P91 thick plate.

I understand the issues around Ni+Mn and its effect on PWHT temperature, but I would like recommendations on quality covered electrode makers for this job.
The client has a small PWHT oven with all the necessary instrumentation and strip chart recorder, but should I insist on at least one TC attached directly to the weld? I'm not sure measuring only air temp gives enough control for this material.
On a related subject, has there been a determination of the mechanism and causes of SCC cracking of P91 after welding and before PWHT? For this job I have advised the client to clean the test plate and just store it in their rod oven until ready for PWHT. After cooling below 200°F and bakeout of course.
I also plan to do a Vickers (1kg) hardness survey. Any specific guidance on this, other than covering all the zones along the top and bottom surfaces?

Thanks in advance.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

RE: P91 Welding Consumables & Questions

I would use Metrode welding products for Grade 91.
http://www.metrode.com/en-gb/products.html

Regarding PWHT, you should have several TC's attached to the product at various locations and a survey of the furnace before you attempt PWHT of Grade 91 because of the response of this material to improper PWHT and PWHT temperature tolerances.

If you don't want to bother with a temperature profile survey of the furnace send the component to a reputable heat treater that knows and understands Grade 91 material.

If you decide to send the welded component out for PWHT, perform a post weld bake (500-550 deg F) for 1 hour minimum to remove any hydrogen to reduce the risk of SCC. The problem of SCC usually develops when an as welded component is exposed to high humidity, hydrogen introduced during welding or condensate before PWHT.

RE: P91 Welding Consumables & Questions

There is some good hardness testing guidance in API RP 582, 2009. You may want to consider a 10kg Vickers load.

RE: P91 Welding Consumables & Questions

We have used Metrode, Bohler and more recently (last 10 years) specific ESAB filler metals (the initial fillers were not considered acceptable)

RE: P91 Welding Consumables & Questions

We collaborate with Bohler.
We used for material X10CrMoVNb9-1 (Werk. 1.4903) the following filler materials: 1. GTAW - Trade name: BÖHLER C9 MV-IG; 2. SMAW - Trade name: BÖHLER FOX C9 MV

RE: P91 Welding Consumables & Questions

Bruscato factor and Mn:S ratio should also be considered in your filler selection as well as Mn+Ni.

RE: P91 Welding Consumables & Questions

Hi Brimstoner,

As per B-31.1-2016, recommended PWHT temperature for welds P-91 grade is (P-No. 15E, Group 1) 1,350 to 1,425 F (730 to 775 C).

With respect to Ni+Mn content the requirements of the above code are as follows and looks to be quite strict ascompared to the earlier versions of the same:-
-The Ni+Mn content of the filler metal shall not exceed 1.2% unless specified by the designer.If so the maximum temperature to be reached during PWHT shall be the A1 or AC1(lower critical temperature) of the filler metal, as determined by analysis and calculation or by test, but not exceeding 1,470°F (800°C).
-If the 1,470°F (800°C) was not exceeded but the A1 or AC1 of the filler metal was exceeded or if the composition of the filler metal is unknown, the weld must be removed and replaced.
-It shall then be rewelded with compliant filler metal and subjected to a compliant PWHT.
-If the 1,470°F (800°C) limit was exceeded, the weld and the entire area affected by the PWHT shall be removed and, if reused, shall be re normalized and tempered prior to re installation.

Hence the onus on electrode manufacturers to manufacture electrodes/fillers conforming to the code requirements are more.At the same time fabricators need to send these requirements beforehand to consumable manufacturers to get the right electrode meeting the design requirements.However all reputed manufacturers are aware of thies requirements.

I've attached some extract from Esab's literature, hope you'll find the highlighted texts interesting.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.

RE: P91 Welding Consumables & Questions

(OP)
Thanks for the Code update, pradipgoswami
Looks like the quality consumable makers were already aware of the PWHT issue and have been formulating accordingly.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

RE: P91 Welding Consumables & Questions

Hi Brimstoner,

Thanks for your response.There had been many developments with respect to the welding consumables for Grade -91 steel over the years. The push for developing newer consumables & incorporating the same to the design codes is always from the consumable manufacturer's side.Such developments are always better for the OEM, consultants and the utility, in the end the plant reliability is always better.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.

RE: P91 Welding Consumables & Questions

I would use a p91 filler metal and PWHT at 740ºC

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