Subject: FW: [MW:3815] RE: 3807] Welding of P5A & P5B Material
Date: Thu, 10 Dec 2009 16:58:43 -0500
From: pradip.goswami@opg.com
To: pgoswami@sympatico.ca
Dear Friends,
I put some useful information on the first part of the query- SA 335 Gr. P91 (PNo-5B, Group No-2)
- What is the Preheating Temperature? 400F (200C)
§ Application of elevated preheat and PWHT, including interpass temperature controls, are absolutely necessary with Grade 91 weldments, regardless of diameter or thickness. The literature suggests that 2000C (~ 4000F) is adequate for preheating P91 weldments. Fabricators typically aim for 2500C (~ 5000F) but will go as low as 1500C (~ 3000F), for root and hot pass layers only, thin-walled components or where GTAW is utilized.
§ Interpass temperatures normally are restricted to 300 to 3500C (600-7000F).
- What is the Post heating Temperature & Time (Extract from API Technical Report 938-B)
§ PWHT performed at 760ºC ± 14ºC (1400ºF ± 25ºF) for utility services is typically performed for at least one hour for wall thickness less than 13 mm (½ in.). For wall thickness greater than 13 mm (1/2 in.), PWHT holding time is about 2 hours. For wall thickness greater than 50 mm (2 in.), PWHT holding time is minimum 2 hours plus one hour for each additional 25 mm (1 in.).
§ For process services and in order to meet the above mentioned hardness requirements, the holding time is typically six (6) hours minimum. To avoid over-tempering and softening thin wall material [e.g. < 12.7 mm (< ½ in.)], shorter minimum holding time is usually established during pre-production welding procedure qualification. It is good practice to determine PWHT holding time based on testing of welding procedure qualification.
§ Generally PWHT shall be conducted within a narrow band and it should not exceed the tempering temperature of steels, which would soften the steel ,causing a loss of creep properties in service.
- PWHT is required or not-
§ PWHT is required always, irrespective of thickness. Look at TABLE-132 of ASME B31.1 , no exceptions allowed.
- While welding (GTAW) Backing is required
§ GTAW backing is always required, steels with typically 9Cr-1Mo will get highly oxidized, causing a loss of corrosion properties. Even in the unities (under steam) if the water chemistry is not balanced proper, stress corrosion crack or other forms of corrosion may occur. Hence it is always a good engineering practice to Argon. purge the root .
- Typical Welding Cycle for welding P-91 steel:- As recommended by Book. For thinner sections(≤ ½") immediate PWHT may be deferred after performing DHT(@ 300-3500C ,2hrs minim) and storing in dry environment(helps to avoid SCC).
- Criticallities of P-91 Steel- Though classified under Cr-Mo steels in various codes, P-91 steel is totally different than say P-22 steel with respect to welding metallurgy, hence extreme care should be taken, for materials specification, welding consumable selection, qualifying the Code required variables etc.An extract from one of the leaders on P-91 in north America sugegsts recomemnde the following
Comparison of Important Variables when Welding P(T) 22 versus P(T) 91.
| Variable | Base Metal | |
|
| P(T) 22 | P(T) 91 |
| Preheat | Always | Always ! |
| PWHT | Sometimes (some code exemptions) | Always ! |
| Normalize & Temper (after bending or cold working) | Sometimes | Always ! (> 18% strain) |
| Certified Material Test Report | Rarely (not normally required) | Always ! (PWHT < AC1) |
| Toughness Requirements | Rarely (not normally required) | Always ! |
| Post Bake | Rarely (not normally required) | Always ! (except GTAW) |
| Cool < 1000C before PWHT | No (not required) | Yes (pending further study) |
| Bead Sequence | Rarely (not normally required) | Always ! (interbead tempering needed) |
| Purge | No (not normally required) | Always ! (material will sugar) |
Hence P-91 is always a challenge to a welding engineer.
Thanks
Pradip Goswami,P.Eng
Senior Engineer/Specialist(Welding-Metallurgy)
Machine Dynamics & Component Integrity Dept.
Engineering & Training Services Division
ONTARIO POWER GENERATION Inc.
PO Box-2000, RR-55(South)
Nanticoke, Ontario,N0A1L0
Tel:-(519) 587-2201, Ext 3107--in Nanticoke
(416) 231-4111, Ext 5925--in Kipling,Toronto
Fax: (519) 587-6814
-----Original Message-----
From: pgoswami@sympatico.ca [mailto:pgoswami@sympatico.ca]
Sent: Thursday, December 10, 2009 6:23 AM
To: GOSWAMI Pradip -FOSSIL
Subject: FW: [MW:3815] RE: 3807] Welding of P5A & P5B Material
> Subject: [MW:3815] RE: 3807] Welding of P5A & P5B Material
> Date: Wed, 9 Dec 2009 08:59:10 -0600
> From: jhenning@deltak.com
> To: materials-welding@googlegroups.com
>
> See below -
>
> -----Original Message-----
> From: materials-welding@googlegroups.com
> [mailto:materials-welding@googlegroups.com] On Behalf Of KC
> Sent: Wednesday, December 09, 2009 1:44 AM
> To: Materials & Welding
> Subject: [MW:3807] Welding of P5A & P5B Material
>
> Can any body inform about the .....
>
> For the welding of SA 335 Gr. P91 (PNo-5B, Group No-2) Material.........
> 1) What is the Preheating Temperature? 400F (200C)
> minimum
> 2) What is the Post heating Temperature & Time ? Typical 1400F
> +/- 25F (760C +/- 15C)
> 3) PWHT is require or not ? P91 should
> always be PWHT'ed, only exception - ERW tube finning with qualifiers
> 4) While welding (GTAW) Backing is require if yes, then Argon is OK
> ? P91 open root welds should always be gas backed with Argon due to
> high Cr.
>
> For the welding of SA 335 Gr. P22 (PNo-5A, Group No-1) Material.........
> 1) What is the Preheating Temperature? 300F (150C)Code
> minimum, I recommend 400F (200C)
> 2) What is the Post heating Temperature & Time ? Depends on
> Code: Sec I or VIII 1250F (675C) min.; B31.X 1300F (705C) min.
> 3) PWHT is require or not ? Depends on (1)
> Code and then (2) thickness, (3) diameter, and (4) type of weld -
> insufficient detail
> 4) While welding (GTAW) Backing is require if yes, then Argon is OK
> ? Not required by Code, some customers want it others do not. My
> opinion is that Cr content low enough it is not really required except
> perhaps for highly aggressive corrosive environments certainly should
> not be necessary for steam service.
>
> --
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> The views expressed/exchnaged in this group are members personel views
> and meant for educational purposes only, Users must take their own
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>
> --
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> The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
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