Alternative body valve material 1

[Johnrem]

Hello Specialists;

Can ASTM A487 Gr 4C be alternative material (valve body material ) to A216 WCB specified in Client Piping Material specification?
In other words the problem is as follows: Client piping specification stipulates A216 WCB as check valve body matrial. Vendor is propsing A487 Gr 4C. Shall I accept or not.

Service: Gas injection
design pressure: 450 bars@70°C
Gas: Not coorosive

 

[rneill]

ASTM A487 material is generally much higher strength than A216 so given your design pressure, it was probably selected for that reason. However, this is not a listed material in ASME B16.34 so the valve would not be able to be stamped as an ASME B16.34 valve if that is a consideration - depending on the valve standard it is made to, it might be considered an unlisted component under B31.3.

In sour (containing hydrogen sulfide) service, the material may be questionable since the high strength may lead to problems meeting NACE/ISO requirements.

Other than sour service, I can't think of a general problem with the material right now.

Ultimately, doesn't the client need to accept or not since it is his specification that you would need a waiver against?

 

[Johnrem]

Rneill
Thank you very much for your helpful advice.
1) The valve is check valve under API 594. The valve will be installed in gas injection wellhead.
Yes A487 Gr 4C is not a listed material in B31.3, onlr A487 CA6NM is listed there. This material is not listed also in B16.34.
Please can you advise the of accepting an unlisted material?

2) During our clarifcations with Vendors, we very often met such problems. Almost all Vendors proposed to us alternative materials for valve body, trim...etc.
Can you advice the generals rules governing acceptance or rejection of alternative materials that Vendors proposes.
I know that SS can't be substitud by CS or low temp CS and low temperature CS can't be substitude by CS. But when both material (requested and propsed one) belongs to same family, I can't make judgement. Are SMYS and UTS only the points to check?

3)What will be the problem if the valve will not be stamped B16.34?

4) if A487 Gr 4C is acceptable as alternative to A216 WCB, why do you think that Client may reject waiver to his specification.

Thanx alot

 

[rneill]

1. What is the design code that you are required to work to - is it B31.3? Assuming yes (which is not necessarily the case since you indicate this is at a gas injection wellhead), you would look at Table 326.1 to determine the listed component standards. Something is either on that list or not. If it is on the list then liability for acceptability of design and materials is substantially reduced as the component is "pre-approved". If it is not on the list then the "designer" is responsible to ensure that the component meets all the requirements of B31.3 (see Clause 326.1.2 and 326.2.2). In this case, API 594 is a listed valve standard so you don't need to worry about this issue.

2. It is very difficult if not impossible to provide a comprehensive set of rules regarding what substitutions may or may not be acceptable. This will be highly dependent on the specific circumstances of each job. Some of the more important things you have to consider are:
- Do the materials have equivalent low and high temperature ratings (impact test values for example)
- Do the materials have similar mechanical properties such that they have the same pressure ratings
- What are the possible considerations with regards to the service environment (e.g., susceptibility to problems in H2S service)
- Are the materials of the same type (e.g., forgings, castings). Some clients will not accept castings in place of forgings unless they receive supplemental examination.
- Do the materials have similar weldability

Note: one common mistake I've seen people make is to accept SS valves as a substitute for CS not realizing that SS flanges have lower pressure ratings than CS flanges and so they then should be derating the entire piping system and resetting their PSV's.

3) that depends on the client and the clients specs. Somewhat addressed by my point 1 above. If the client specified B16.34 then it is a contractual problem and the client may reject a valve that does not comply. It is common for B16.34 to be specified but it is also extremely common for API 594 to be specified. One possible issue is that B16.34 specifies the required wall thickness of the valve body but API 594 does not. This means that a valve purchased to B16.34 is assured of meeting a minimum standard. A valve made out of A487 material to API 594 is subject to the discretion of the manufacturer and so depending on whether the manufacturer is trying to save money, may have a less robust design - there is no specified minimum design wall thickness.

4) It is not clear that you can positively state that A487 Gr 4C is an acceptable alternative to A216 WCB. They are different materials and there may be some technical reason that the client has (that neither of us is aware of) that makes the A487 material unacceptable to him and to be honest, while it might be nice if he did, he is under no obligation to justify his rejection of a material that does not meet the contracted specifications. Myself, I'm not intimately familiar with the properties of A487 (nor do I have any detailed information on the service) and so without comparing the A487 and A216 standards side by side can't positively comment on whether A487 is an entirely acceptable substitute. There may be differences in heat treatment requirements, in examination and inspection requirements, etc.

The Client may reject your waiver on non-technical basis as well. I've been on the client side many times and on a large project you are inundated with so many requests for deviations and exceptions to project specifications that you simply cannot respond to every one. I've often been forced into the situation (purely on the basis of time management) of refusing to review deviation requests unless the person putting forth the request can demonstrate that the original technical requirement could not practically be complied with.

Another possible reason for rejection is that the client representative simply does not have the technical expertise to evaluate the proposed recommendation and it may cost him/her money to get impartial third party advice. Since they have a contract in place that specifies a technically acceptable product, which is available, they may not see why they need to spend time and money evaluating alternatives.

 

[Johnrem]

Rneill,
Thank you again for your nice explanation. However I've to disturb with some questions as follows:
1) I confirmed that our gas injection system is under B31.3 code near the wellhead and under B31.8 for flowline in the desert.
Table 326.1 in B31.3 includes standard API 594. A487 specification is listed in Appendix A of B31.3 but the grade 4C of A487 is not listed in Table A-1 "Basic Allowable Stresses". Only grades CA6NM and Cl.A are shown on Table A-1. Under these considerations shall I consider grade 4C as unlisted material or not?

2) I can't understand why you said that some time clients refuse castings in place of forgings. I used to accept such deviation many times provided that casting and forging belong to same group (example: A216 WCB instead of A105 and vice versa). Am I wrong to do that?

3) Regarding SS valve as Alternative to CS: you said that it is a mistake to do that.
I think we can substitute CS by SS without derating the entire system provided that design pressure/temperature of the piping system is covered by the SS flange pressure-temperature rating given in B16.5 or B16.34.
Example: a piping system having design press=410bar, design T°=38°C. For me, A 351 Gr. CF8M can replace A216 WCB as a material for valve body since class 2500 pressures in both ''Group 2.2 Materials'' and ''Group 1.1 Materials'' are bigger than piping system design pressure. Is my idea correct?
4) If my understanding is clear, you can't ensure that A487 Gr 4C is technically acceptable as alternative to A216 WCB. You said also we have to compare these two materials side by side in order to take a decision. Can you indicate me which properties shall I compare side by side in order to take a decision. Forget about cost effect and Client specification, just let focus on technically point of view.

Thank you again Rneill

 

[rneill]

1. If the specific grade is not listed, it is an unlisted material.
2. You are not necessarily wrong but castings are much more likely to have detrimental defects than forgings. In some critical services, I specify forgings and will accept castings only with supplemental examination - this is not an uncommon practice. If I recall, the Exxon specs require supplemental examination of all castings meeting certain criteria.
3. I didn't say it was always a mistake - just that it was sometimes done without considering the reduced flange rating (which is a mistake). There may also be services where CS is suitable but SS is not (e.g., some sour services).
4. Put the two specs side by side and see what's different between them (they are short documents) so compare everything and consider the effect of the items that are different.