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Pipe Fittings - Carbon content restriction in the steel used
2

Pipe Fittings - Carbon content restriction in the steel used

Pipe Fittings - Carbon content restriction in the steel used

(OP)
A typical client spec for CS Pipe fittings used in the Upstream Oil and Gas industry reads as, "All carbon steels, including normalised steels, used for the fabrication of fittings shall have a maximum carbon content of 0.23 %."

ASTM A234 Gr B or C, generally used, has a C content of 0.3 to 0.35 max restriction.

How can this restriction be imposed, unless a custom mill order be done with the Carbon content restricted during the steel making process.

The Procurement description of the item that comes of the material management application (Marian or the Smart Plant Materials) does not have this stated.

A generic requirement stated as an overall requirement in the client specification. I am just wondering, will this requirement get addressed to the manufacturer or supplier? The only time this would probably gets checked is when it is offered for inspection, when it is too late for any change.

An Industry standard fitting can have the C content in the range allowed by the ASTM Spec. Or, is it that the C content is invariably restricted to 0.23% irrespective of what it says in the ASTM A234, even if the component is off the shelf.

I need to see the ASTM A960 which defines the buying description for A234 and a typical MTC for a A234 fitting.

Any thoughts as to how this works out?


RE: Pipe Fittings - Carbon content restriction in the steel used

Add the max carbon content to your purchase order as a requirement (or better, to your RfQ), so your supplier can determine on a MTR per MTR basis if a certain heat meets the requirement (and can be delievered to you) or not (so shall not be delivered).

RE: Pipe Fittings - Carbon content restriction in the steel used

Is the fitting for the low temperature process?
The low carbon content material could be specified for the low temperature with better ductility. Check B31.3 for the suitable material, such as A420.

RE: Pipe Fittings - Carbon content restriction in the steel used

XL83NL has it correct. You will pay more for the controlled carbon content.

RE: Pipe Fittings - Carbon content restriction in the steel used

(OP)
Thanks for your thoughts.

From the text of the client statement, it appears the requirement is weld ability.

The C max Content requirements of ASTM A106 is Gr A : 0.25, Gr B : 0.3, Gr C : 0.35. Would it not be better to opt for Gr A, but the trade off is the corresponding material strengths. By restricting the C max, the intent may be to compensate the strengths with addition on Mn. What is the change in the weld ability attribute in doing so.

In any case, the buying descriptions do not include requirements of constituent chemistry. A Valve would have a data sheet to specify more specific attributes, but not a piping bulk item. This is customary.

RE: Pipe Fittings - Carbon content restriction in the steel used

It may indeed be weldability. The increase in Mn will increase the strength in lieu of higher carbon content. From a welding standpoint no issues.

RE: Pipe Fittings - Carbon content restriction in the steel used

(OP)
I looked up the A960 referenced in A234 and it does not require any chemistry to be stated as a buying specification for the A234 fitting.
Also by reviewing a sample set of MTC for A234 Gr B material shows that the C content invariably is around 0.18. Therefore gets acceptable for the imposed 0.23.

My point was why an important attribute for the material is not specified in the material description itself, than in a referenced specification.

The reasoning is the above.

RE: Pipe Fittings - Carbon content restriction in the steel used

The reason is that the client believes that a specific restriction over and above the requirements of the base ASTM standard is warranted to ensure satisfactory performance. For example, the restrictions could be for sour service applications.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Pipe Fittings - Carbon content restriction in the steel used

(OP)
If a SOUR service restriction exists then it should be stated so in the ISO 15156. In this case, it is only the weld ability that is cited as the reasoning by the client. If there is a real weld ability problem with a A234 component C content, how is that it is included in the A234 as a material for pipe fittings intended for welding to CS pipe. The 0.23 C requirement is a preferential one. In this case it so happens that the C content in any standard fittings of WPA, WPB or WPC have identical C content well below the 0.23 limit set.

RE: Pipe Fittings - Carbon content restriction in the steel used

svi - why don't you discuss this with your client? It really makes no difference what is posted here, the client decides.

RE: Pipe Fittings - Carbon content restriction in the steel used

(OP)
how much of a weldability advantage does the 0.25 or 0.18 C provide over the 0.3 or 0.35 C?

RE: Pipe Fittings - Carbon content restriction in the steel used

Carbon is the one element that has an immediate impact on strength of the weld and weld region. Along with it comes sensitivity to cracking and precautions required like preheat and possibly PWHT. This is why ASME Code limits the carbon content to 0.35% max. If carbon needs to be reduced, other alloy elements are added but they do not directly compensate for strength like carbon.

RE: Pipe Fittings - Carbon content restriction in the steel used

(OP)
A typical material test certificate from Nippon Steel for API 5L Gr B / X42 PSL1 reads as,
Composition : C 0.19, Si 0.18, Mn 1.07, P 0.013, S 0.005, Cu 0.002, Cr 0.004, Ni 0.003, Mo 0.002, Ca 0.001, Ceq = C + Mn/6 +(Cr+Mo+V)/5 + (Cu+Ni)/15 = 0.42
Tensile
YS : Spec min 42.1 ksi, actual : 51.3 ksi
TS : Spec min 60.2 ksi, actual : 74.4 ksi
El : Spec min 27%, actual : 42%

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