SA 240 904L, N08904, SB 625

[r0nciS]

I just want to know the difference of the three if there is. The process specify 904/904L sstl for the shell of heat exchanger and as mechanical, I'm confused what to input between the three. Is there any restrictions?.

Thanks.

 

[metengr]

Please carefully review the material specifications for information SA 240 and SB 625. Review the scope of each.

 

[pradipgoswami]

904L(UNS 08904) is a super austenitic stainless steel with high degree of corrosion resistance especially in various acid medias, most notable are phosphoric and sulfuric acids.
As mentioned by metengr earlier, this specification is covered in Sec-II,Pt-A,SA 240.

Alloy 625 is a versatile austenitic nickel-chromium- molybdenum-niobium alloy with exceptional corrosion resistance and high temperature properties. By all means alloy 625 is a higher end alloy as compared to 904L. It could replace 904L if required. However selection and restrictions on use of these alloys are based on the various corrosion properties in the process media as defined by the designer or the process licensor.The cost factor vs equipment life is also to be considered. The following links provide brief but pertinent information on these alloys.


What're the process environments, and the various design parameters?

Thanks

http://www.atimetals.com/Documents/ati_904l_tds_en.pdf

http://www.sandmeyersteel.com/images/Alloy-625-Spec-Sheet.pdf

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[metengr]

I don't believe the comparison is with Alloy 625, it is with specification ASME SB 625 Grade N08904.

 

[r0nciS]

yes..it is not alloy 625 but SB 625 with UNS no. N08904..SB 625 is the corresponding plate/sheet material in ASME for SA 240 904L...

 

[metengr]

Did you read the specifications?????????? One is for pressure vessels (904L), the other is not. Look at dual certification, if possible.

 

[r0nciS]

I want to know the corresponding ASME material of N08904/904L for flange forging..thanks

 

[r0nciS]

alloy 625 (UNS N06625) is different to SB 625 (UNS N08904)

 

[metengr]

For flanges, look at ASME B16.5, N08904 is under SB 649. SB 625 is for plates.

 

[Cheops]

Can anyone explain the difference between SA-240 N08904 and SB-625 N08904? The first is listed as Austenitic Steel and it is NOT listed in the allowable stress tables of ASME Sec II table 1A. It is also NOT listed in table UHA-23. The second is listed as a non-ferrous material under both UNF-23.3 and ASME Sec II table 1A.

From what I can see, only SB-625 N08904 is OK for use for pressure vessels. But then, on what grounds can we tell a Fabricator who has already purchased SA 240 N08904, that this material is not acceptable??

I must say that, despite my 30+ years in design of pressure vessels, I am puzzled by this dual classification for the same chemical composition.

 

[marty007]

Hey Cheops,

I have recently been wracking my brain about this exact same material... see my thread on forgings: Link

I vaguely remember hearing from another engineer that ASME was planning on moving 904L from the SB specs over to the SA specs. Hence you see N08904 is both SA specs and SB specs (not neccessarily in ASME IID, but you'll find them in ASME IIA and ASME IIB:
Plate: SA-240, SB-625.
Forgings: This is a weird one, because you'll find 904L in SA-182, but it's not in the IID stress tables. In fact there are no forging specs in the IID tables.
Pipe: SA-312, SB-673,674,677.

I'm not aware of whether this is addressed in the new version of ASME 2013 that's coming out soon, but I sure hope it's all fixed up.

metengr:
When it comes to flanges, the latest version of B16.5 actually calls out calls out A479 for forgings and A240 for plates (A479 isn't even a forging spec, and N08904 isn't even mentioned in A479!)

Side note: I've sent an inquiry to the B16.5 Committee asking specifically about the forging spec, I feel that it should be A182. We'll see what they come up with.

Cheers,
Marty

 

[Cheops]

Thanks Marty.

I agree with you that B16.5 should refer to A 182, not A 479.

Classification under different material specifications has created a lot of confusion for a Fabricator I am working with. I hope this issue is addressd in the 2013 edition of the Code!

 

[EdStainless]

904L is a stainless steel, it has more iron in it than any other element.
But it is less than 50% iron. At some time back in the old days it was given a N UNS number and put into the B specs as non-ferrous.
This is being changed. These stainless grades (some of the 6% Mo alloys are this way also) are being moved into the A specs in ASTM. Then as these are adopted by ASME they will appear in the SA specs.
Eventually the B and SB references to these alloys will be removed. They have only been working it for about a decade, so it will still take a while.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Cheops]

Thanks EdStainless for shedding the light on this issue.

Cheops