Sachin,
As per UCS-79- Vessel shell sections, heads, and other pressure boundary parts of carbon and low alloy steel plates fabricated by cold forming shall be heat treated subsequently (see UCS-56) when the resulting extreme fibre elongation is more than 5% from the as-rolled condition and any of the following conditions exist i.e. thickness of the part before cold forming exceeds 5⁄8 in. (16 mm).
By default ASME Sec VIII, DIV-1 code recommends Stress Relieving as post forming heat treatment also by NACE MR-0103-2007). For certain services, especially for wet H2S environments in refining and other sour environments, based on client (oil refiner's experience) heads should be fully normalized followed by SR (which would be performed while PWHT the whole vessel). My feel is this requirement is to :-
* nullify any localized residual stresses, which may generate during excessive forming
* cause uniformity of grain size and improve mechanical properties
I've come across this (NR) requirement in many oil clients' spec in the past. If you get hold of Shell's spec:- DEP 31.22.20.31-Gen.- Pressure Vessels (Based on ASME Section VIII) specifies: clearly:-
* All parts which have been cold formed by more than 5 % shall be subjected to an appropriate normalizing treatment and, if necessary, a tempering treatment.
* Normalizing of carbon steel components and base materials shall be performed separately and not as part of hot-forming operations, unless the finishing hot-forming temperature is in the normalizing temperature range of 850 °C (1560 °F) to 960 °C (1760 °F).
As EIL have pioneered many refinery construction and engineering in India for many years, they also incorporated this requirement in their specification 6-12-0002.I would guess that the cut off requirement of 16mm (5/8") comes from SecVIII, DIV-1 cut-off criteria.
Dished heads below 16 mm(5/8") may be subjected to SR, unless specifically asked by client (oil refiner).
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net
________________________________
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of sachin sankhe
Sent: Friday, October 22, 2010 11:49 AM
To: materials_welding
Subject: [MW:7718] Normalizing requirement
Hi,
As we all aware that ASME Sec VIII Div.1 do not speak on normalising requirement
Then when we say Normalising is done at 910 Deg.C and with holding time as 1mm/min, then what is the basis for the same.I mean acceptence code
Futher to this ASME Sec VIII Div1 says that if due to cold forming fibre elengoation is more than 5% then heat tretment as per UCS 56 to be done.However most of the client spec mention that normalising need to be carried out.
I feel that for small thk say 12-13 mm normalising is not appropriate and may warp the matereial.So in that case can we accept stress relieving?
In EIL spec normalising is mentioned above 16 mm if fibre elongation is more than 5%
Request you to clarify above query giving reference of code
Regards
Sachin
Regards
Sachin.Sankhe
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