LTCS_average_grain_size

[Giuss]

Dear all,

we lost traceability on some small pup-Pieces and we are not 100% sure it is LTCS (A 333 gr 6) as per line requirements or if CS (ASTM A106 gr B) was used. We can not make destructive examinationand we proposed to verify it by the means of grain size measurement (ASTM E112) of metallographic replicas.
Could someone tell me wich should be the minimum grain size according to abovesaid std in order to esatblish it is A 333 or at least we could be confident that the installed material is tough enaugh to be comparable to a LTCS.
we suppose that from grain size 5& above we could have good confidence, what do you think?

Thank you very much


Giuss

 

[ad101]

Hi Giuss..

What is a pup-piece? I'm not familiar with either of these specific grades..but I don't think you're likely to get a particularly useful answer to minimum grain size. A hardness test might be a better place to start- can you compare the result to another part which you do know the spec of?

Adam

 

[metengr]

A pup piece is a slang term for pipe lengths that are short and used to extend a pipe or provide for improved fit-up. In this case, the pup pieces were unmarked because someone forgot to transfer mill markings - this happens often.

I am afraid you will not be able to sort between A 333 Grade 6 and A 106 Grade B using any method without impact testing. Why? Look at the mechanical properties between these two steels and you will find them to be nearly identical, so hardness will not be reliable for sorting.

Grade 6 Grade B
UTS 60 Ksi 60 Ksi
YS 35 Ksi 35 Ksi

 

[MikeMet]

Grain size is not a reliable indication of low temperature impact properties. You need to do testing.

 

[Giuss]

MikeMet, i do not think so.
By a qualitative and quantitative (grain size determination) metallographical analysis plus a chemical analysis i should be very confident:

-Grain Size
-Heat treatment
-Chemical (low presence of impurities (S,P,etc) or high content of deoxydized (e.g. Al>0.02%) or ratio Mn/C with the same Ceq or may be Ni presence.

I do not think there are other factors (excluding the geometric ones) influencing toughness of a low carbon steel.

Obviously i will not sure if the material was purchased according A106gr B or A333 gr 6 but i will be confident that the installed material should not have a brittle beahviour in typical range of temperature covered by LTCS.

Giuss

 

[metengr]

Guiss;
What is your minimum design metal temperature and pipe wall thickness for the above? If MDMT is at or above -29 deg C don't worry about impact properties because the SA 106 Grade B will have adequate notch toughness.

 

[MikeMet]

Guiss;

You are right, but you won't be right every time, hence it is not a reliable means to ensure that any given material meets charpy or mechanical property requirements. I have seen low alloy steel and carbon steels that look great have problems meeting properties, especially at low temperatures. What limit would you put on impurities? Sometime even elements that have limits in the ASTM Specs can cause problems with low temperature properties. Sometimes you have to adjust the normalizing and other heat tretment procedures to make properties for a given chemistry. You simply don't know how even the smallest amount of grain boundary constituents will react unless you test.

Are you willing to put your reputation and the safety of employees on the line based on only metallurgical and chemistry of a low temperature installation? If you are, then tell where every installation is that you have designed and I will stay away.