[MW:6455] Difficulties in meeting API publication 938A requirements for 1.25Cr-0.5Mo requirement

Dear Mr. Pradip Goswami

 

Thank you for your time and effort on this detailed explanation.

MPCF 5 or 7, how can we consider which is low and which one is high?

as per my understanding the values given for MPC 5 & 7 are 2 and 0.5 could be cut off values and value greater than this to considered as high MPCF to evaluate PWHT temperature as per fig-1

 

On page 3 of this publication it states as limiting factor, where as in Appendix E (page 114) states this value being the cut off for high low considerations.

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of pgoswami
Sent: Saturday, August 07, 2010 8:17 AM
To: materials-welding@googlegroups.com
Subject: [MW:6344] FW: 6186] Difficulties in meeting API publication 938 requirements for 1.25Cr-0.5Mo requirement

 

Mr.. Bathula,

 

This document is a part of the activities  on 1.25Cr-0.5Mo taken around late 1990's by API and MPC and is a very well researched document. However you know that steel making practices and the resultant metallurgical properties have changed a lot over last 15 years.

 

API-938A specifies, Materials Composition Factor (MPCF), which is a combination of controlling  C, tramp elements causing embrittlement - e.g - Sn,As,Sb and S& P (also causing poor toughness and high temperature embrittlement) .MPCF has great influence on cracking behavior. Typically @ C≥   0.15% and with higher levels of tramp elements, cracking possibilities are more for 1.25Cr-0.5Mo class 2 plates and min PWHT @ 1325⁰ F is recommended.MPC should be between 5-7.

 

 Another important formula from this document is  Cracking Parameter, PSR = Cr + Cu + 2 x Mo + 10 x V + 7 x Nb + 5 x Ti – 2, when it's > 0, material is more susceptible to cracking, which calls for a good control on trace alloying elements.

 

API later produced technical report 934-D,Technical Report on the Materials and Fabrication Issues of 1¼ Cr - ½ Mo and 1 Cr - ½ Mo Steel Pressure Vessels. Many of the observed problems on this material as listed in this document  have commonalities with API-938.  As you know research papers or technical reports are difficult documents to follow for any engineering projects and technical specifications are more appropriate.

 

API RP934C,- Recommended Practice for Materials and Fabrication of 1 1/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High Temperature, High Pressure Hydrogen Service is adopted by all oil and gas industries in general .It had refined and incorporated all the observations of API-938A . Some of the requirements of API RP-934  are:-

 

·         X – bar < 15 ppm, Where X – bar = (10P+5Sb+4Sn+As)/100, P, Sb, Sn, and As  reported  in ppm]

·         C = 0.15% max, P = 0.007 wt% max, S = 0.007 wt% max, Cu = 0.20% max, Ni = 0.30% max

·         All product forms shall be normalized and tempered (N&T) or quenched and tempered (Q&T).

·         For >2" (50 mm), Q&T is typically required to meet the properties specified in RP-934C. Usually Tempering shall preferably be done at  temperatures that is more than PWHT temperatures..

 

Some extracts from Oil Majors Specification on Cr-Mo steels (1Cr-1/2Mo and 1/4Cr-1/2Mo)  for Hydrogen Services are  and would be of interest :-

 

A.     A  Leading  Canadian Refiner 

1.     The materials used for fabrication of the pressure envelope shall be Quenched and Tempered (Q&T).

2.     Chemical analysis for each material heat. As a minimum the analysis shall present the concentration (%) of the following elements; C, Si, Mn, Cr, Mo, V, Nb, Ti, Cu, Ni, P, S, Sn, Sb, As.

3.     The materials shall have the following restricted chemistry;

·         C < 0.15%

·         Cu < 0.20%

·         Ni < 0.30%

·         P < 0.007%

·         S < 0.007% or (S+P < 0.014%)

·         P_SR = Cr + Cu + 2 x Mo + 10 x V + 7 x Nb + 5 x Ti – 2 < 0

·         X bar = (10 x P + 5 x Sb + 4 x Sn + As) / 100 < 15

 

B.    A Global Oil  Refining Company:-  Additional requirements for pressure vessels constructed of all grades of chromium-molybdenum (Cr-Mo) steels. These requirements shall apply to pressure vessels regardless of whether they are in hydrogen service. For heavy-wall pressure vessels constructed from 1¼Cr-½Mo, see API RP 934C.

 

Materials:- 1.25 Cr - 0.5 Mo steel plates-A 387 -11, Class 2-  to be normalized and tempered or quenched and tempered Specify: Cu 0.20% max. Ni 0.30% max. (%Si+% Mn) ≤1.10, (%Si+%Mn) x (%P+%Sn) x 10⁴  ≤ 150.,Specify P-0.005% max.

 

 

I would think  the present API standards as mentioned above and ASME Sec-II ,Part-A, SA 387 (supplementary requirements) addresses very well the concerns raised initially  in 1996 report on API-938A.  

 

Some of the  major  steel mills (see the attachment) have already incorporated these stringencies of  controlled composition in their product specifications  and had been regular participants in API forum on Cr-Mo steels.  

 

Hence upon discussion with process licensor, incorporating requirements of Latest API documents may ease material procurement issue.

 

 

Thanks.

 

 

Pradip Goswami,P.Eng.

Welding & Metallurgical Engineer/Specialist

Ontario Power Generation Inc.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

 

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Bathula Raghuram (Mumbai - PIPING)
Sent: Thursday, July 29, 2010 7:32 AM
To: 'materials-welding@googlegroups.com'
Subject: [MW:6186] Difficulties in meeting API publication 938 requirements for 1.25Cr-0.5Mo requirement

Dear all

Please share your views/experience on API 938 requirements as a fabricator perspective, and difficulties faced for sourcing materials and during fabrication.

In particular composition and PWHT values considering high MPCF.

 

Thanks in adv.