Can an 'H' stainless steel have less carbon compared to its normal stainless steel? ss347H-ss347

[samvanwesen]

Hello!

-a welder in our workshop showed me that his 2'' sch160 pipe had the markings SS347/SS347H on it.

Looking at the material certificate and the corresponding standards(ASTM A312-A376), chem composition can work for either SS347 and SS47H.

What is confusing is what the standard A312 states:
SS347 should have a carbon content of 8%
SS347H shold have a carbon content of 4-10%.

Reading this, I could buy a HIGH CARBON CONTENT SS347H (thats what the H stands for right?), and still have a lower carbon content compared to SS347.
Looking at Table 1 in A312, this goes for all the other H versions of the stainless steels

curious what your guys take on this is.

Thanks!

Sam

 

[XL83NL]

Correct. The H-grade just requires a minimum carbon content (0.04%), whereas the straight grade a max. So theoretically a striaght grade might not meet the H-grade, when C < 0.04%.

What youll see (probably) is that most commercially available 347 pipe is dual certified, as
- it makes it easier for the mill to sell their products (meets both specs)
- most 347 applications require the high carbon content due to Code restrictions
Furthermore there's a difference in Nb content for both grades. This is another difference.

Dual certified is readily available for a lot of common grades, like 304/304L, 316/316L, 347/347H, 321/321H, and also some carbon grades (I think e.g. for A106B/A53B/API 5L).

 

[EdStainless]

It usually isn't done because the window of overlap for C is small, only 0.04-0.08%bu t it is possible.
The Nb isn't much of a problem because the spec is focused on the minimum, there is plenty of room to raise it a bit and meet the requirements.
Another point is that the "H" requires coarse grain size.
I would ask my QA guys to give this another look just to make sure, and I would pull some product tests (chemical and mechanical) to confirm.

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P.E. Metallurgy, Plymouth Tube