CF8M - A351 vs A743

[HowJoh]

Hi All,

I've been supplied a casting for which the material certificate states that it is A743 CF8M but for my purposes I require A351. The foundry's wishes to send to me an revised certificate but I'm concerned that the standards are not equivalent to each other. I've only a copy of A351 and I'm not a metallurgical engineer so I'm wondering what are the differences between it and the A743 standard with regards to CF8M? If the standards are in fact different I'll need to convey to the foundry the exact reasons why they'll have to recast the piece in order that they're readily willing to do so.

Any and all expert comments and replies are gratefully received.

Thanks for your time and assistance,
Howie

 

[metengr]

HowJoh;
The basic difference between these two material specifications is that A 351 is for pressure-retaining service, while A 743 is for general application, in corrosive service.

What could happen, and I have seen this before, is to have dual certification for the same grade of cast material. What this means is that a particular grade of material is supplied where the chemical composition, mechanical properties and inspection/tests are met for both material specifications.

If dual certification is not possible, I would go back and reject the A 743 due to the fact that it is not intended for pressure-retainig service under Scope.

 

[arunmrao]

Agree with metenr's comments. clearly the foundry has erred in producing a test certificate as per ASTM 743,while the call was for ASTM 351.

However,having been involved in manufacturing of castings for a long time, it would be very harsh on the manufacturer to reject them before giving another opportunity.

If test samples are still available,you may conduct independent analysis or draw samples from castings. Also,if they are pressure parts like a valve body,perhaps you may check for radiography or leak test,before accepting them. This would ensure,that you get a product, conforming to your requirements.

Costs you can charge to the vendor. Hope,this helps.

 

[pwtomlin]

While there are some minor differences in the chemistry between A351 and A743, I would be surprised if the foundry in question actually had separate grades of CF8M for each spec. It is trivial to adjust the internal chemistry ranges to work for either specification. I can't speak to all the requirements for both specs, but as long as the chemistry is suitable for A351 I don't see a problem.

 

[metengr]

There is more to this than just chemistry compliance because for pressure retaining service you need to prove mechanical properties, since this is what generates allowable stress values. One would hope the foundry has extra material to run tensile tests in accordance with Table 2 of A 351 OR in accordance with Supplementary Requirement S12 of A 743. Otherwise, the foundry cannot establish dual certification for this heat.

 

[HowJoh]

Thanks for the comments people, I appreciate your time and effort but is no one able to point to a specific, salient difference between the two standards with regards to this material? Maybe I'm missing something but it seems all the replies were rather general. The wet analysis and tensile test has shown that the casting met the A351 CF8M requirements but as metengr pointed out there's more to the standard than that such as inspection, quench temperatures, furnace type & conditions, weld repairs, etc. The Supplement Requirements are not applicable as they were not a part of the original PO. I'd like to think that the difference between a pressure retaining part and one for general corrosive service is more than semantics and a change to the standard's title and its number.

 

[metengr]

HowJoh;
What more are you looking for? The responses above have indicated going the route of dual certification based on comparison between the two material specification requirements. There are various ASTM material specifications that are generated based on Purchaser/Vendor need and specific service application, there is no one size fits all.

My apologies, but you have missed the boat, if all you can conclude from the above responses is "I'd like to think that the difference between a pressure retaining part and one for general corrosive service is more than semantics and a change to the standard's title and its number".

 

[TVP]

HowJoh,

I agree with metengr, and would like to offer the constructive advice that if you feel the responses are lacking, which they are not, then it costs $39.00 to obtain ASTM A 743 directly from ASTM. My guess is that $39 is a paltry amount compared to the cost of your project.

 

[HowJoh]

The most significant difference is that A351 has tensile property, inspection, and quality requirements not found in A743. A351 references A703 which in turn sets out the testing & analysis methods and requirements. A743 references A781, a general specification for casting used in non-pressurized applications.

The foundry's metallurgical engineer didn't know this either until I sat down with his copies of the standards, went through them myself, and then explained it to him. Seems to me that anyone who offers comments regarding a standard, much less a casting to that standard, should be well versed in said standard.

 

[TVP]

HowJoh,

We all agree with that last statement. Very frustrating.

 

[blacksmith37]

Having been on various ASTM A Committees (and API committees) and heard extensive disscussions on certain phrases and WORDS :I will say it is not reasonably likely that that a causual comparison will detect the nuances of two similar specifications.
I would suggest that the end user may be able to accept a product . He would also have an understanding of legal implications in the use of the product. He may be able to "sign off" on some discrepencies.