Filler metal for root weld by GTAW in P91 1

[pandithan]

we are one of the leading Power piping manufacturer. There is a welding between P91 pipes, when we offered root weld by GTAW with Filler wire ER 90S-B9, the customer who is leading power plant manufacturer wants only ER 90S-B3 instead of B9
what is the advantage in Using B3 in place of B9, creep properties how

 

[metengr]

Ask your customer, they specified it. I would guess that it would have something to do with not having to back purge, and/or to avoid risk of stress corrosion cracking prior to completing the groove weld for P91 material.

 

[Guest102023]

You might want to ask the customer why he doesn't just use P9 piping to match the B9 filler metal?

This sounds like one of those situations where they got burned once and then made an unchangeable rule based on that experience.

 

[pradipgoswami]

Dear Pandithan,

Welding between P-91 to P-91 base metals shall always be done fillers/electrodes of matching chemistry AWS-ER90S-B9/E-9018-B9.
Often clients specify ER-90S-B3 filler or E-9018-B3 electrodes for welding between P-91 to P-22 alloys.This is to safeguard against over-tempering of P-22 base metals, as P-91 requires higher PWHT temperatures as per any code, say,B-31.1, Sec-VIII,DIV-1 or B-31.3.

From all design aspects B3 weld metal will have far less creep strength than matching P-91 weld metal.

Please feel free to drop any further queries on this issue.

Thanks.

Pradip



The following document provides a good overview on P-91 welding.You may refer this as a starting guideline.

http://www.sperkoengineering.com/html/Grade 91 R 10-05.pdf.

 

[pandithan]

Mr Goswami
i too agree for dismilar, but for same materials why they want B3 consumable at root
i have not convinced of any reply.
as per code if we use filler metal which has Cr less than 3 percent, we can go less pwht temp(705 c)
Thanks

Pandithan

 

[pradipgoswami]

Mr Pandithan.

There are tons of examples of P-91 welding with matching filler, which includes, GTAW with P-91 filler.As compared to SMAW,FCAW and SAW, GTAW produces one of the cleanest P-91 weld, with very low O2, Mn:S ratio >50( prevents hot cracking), Total Ni+Mn 1.5% max.
If there is a choice for extremely high and consistent quality, GTAW would be the choice to many fabricators,and in fact many boiler manufacturers especially Japanese, go for Automated Narrow Gap GTAW,for quality with slight sacrifice in productivity.

Using B-3 filler would not be recommended, due to low creep strength, if the super-heater design temperatures is 560deg C or more B-3 GTAW welds would invaribly intiate creep damage in service.

Plus if the PWHT is done @ 705deg C, this would not temper P-91 weld & HAZ at all.The welds may have excessive hardness, typically over 300 HV.

The recommended PWHT for utility services are between 740-760 deg C and if PWHTis done judicoiusly Weld/HAZ could end-up with hardness, of 270-290 HV, which is kind of rule of thumb for power industry.

It may be wise to discuss the issue with your client, and educate them with facts.

The attached link will take you to Metrode website.You may have to regiseter to download the details, in case website asks for.
Metrode and Bohler Thyssen are some of the comsumable leading manufacturers of P-91 consumables in the world.

I have tons of other references on P-91 welding, in case if you need.

Thanks.
Pradip

http://www.metrode.com/product_information/product.htm?PDF=P91TP.pdf&pdetail_id=161273&tptype_id=1

 

[pandithan]

Dear Mr Goswami
Thank u very much for ur reply, as u have mentioned i have come across somany things and currently we are carring out welding on P91 with Thyssen consumables.
Customer not agreed because he has done lot with b3 root and running for years
While doing welding with SAW process we are facing problems of Check Surface cracks, could u pl throw some thing on this issues
thanks
Pandithan
aws-cwi
Over more than 30 years in welding with Domestic and Abroad

 

[pradipgoswami]

Dear Mr Pandithan,

I am sorry for my late response on this issue,as I had some problems with logging in to this forum.
Looking at the description of problem:- it looks like due to a shorter aspect ratio on the capping beads.Aspect ratio is the typically ratio of depth to width of weld beads.
D:W = 1.0 is ideal for SAW beads. If this ratio is less than 1.0,there could be chances of preferential seggregation towards the centre of the bead, thus sometimes causing typically hot cracking. I am not sure how severe it's in your case, but I had noticed in the past these cracks are shallow & are removed by light grinding.

It would be good to hear Thyssen's viewpoint in case you contacted them.

Thw following attachment provides substantial information on various P-91 consumables, which may be of interest to you.

Thanks.

Pradip Goswami

 

[GRoberts]

By "check cracking", are you referring to what is also called "chevron cracking" because the cracks are often at 45 degree angles? If so, that is generally a hydrogen related problem associated with high strength weld metals, which P91 could be considered as it is definitely sensitive to hydrogen. What are your pre-heating and post-heating practices? What are your consumable storage practices? P91 has been known to crack even from the hydrogen introduced by light surface rusting due to condensation if the weld is in the brittle condition before PWHT.