chemical composition alloy percentage tolerance

[Erkamal]

Dear Friends,

I am working as a design engineer in Oil and Gas industry.

Generally in chemical property of steel or other material, Alloy percentage has been given only without Maximum and Minimum condition or sometimes , it has been given only with Maximum condition .

Do any have answer that why alloy percentage has been given with maximum condition? Mean what about Minimum condition also ???

or what standard , I should follow to see alloy percent tolerance......

Kamlesh

 

[redpicker]

Can you provide an example? I've worked in the oil and gas industry for over 30 years as a metallurgical engineer and I don't think I have ever run into a material specification that only had maximum for an alloying element. For residual elements, sure, but not for an alloying element.

 

[metengr]

One example is with ASTM/ASME material specification in the power generation industry, in many carbon and low alloy steel Grades the carbon content among other alloying elements is specified in maximum amount by mass percentage simply because this gives flexibility to suppliers for lowering carbon and increasing other alloy elements to achieve strength level. The ASME code requires 0.35% or less in carbon because of weldability concerns.

 

[arunmrao]

@ RP,

Perhaps he refers to S and P contents, which have a max specified(0.05%Max) or as the case maybe.



"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Erkamal]

Dear Friends,

For example , I have attached the ASTM A105 chemical composition here.

Like Maximum condition of S, Co, Ni, C, ....
what about minimum condition ??
I have seen same condition in other standard also.


Kamlesh

 

[CoryPad]

For low carbon steel pipe, there can be zero sulfur, copper, nickel, etc. and the material will function as required, thus no minimum concentration is needed.

 

[EdStainless]

For trace elements that are not deliberately added and have minimal influence on properties you spec a max. This is usually because if they are too high they will have a detrimental effect.
For example on "L" (low carbon) grades of stainless there is no min for C, you want as little as possible.

There is another issue here, with all alloys. When you analyze a finished product you are allowed a tolerance outside the original specification range. These amounts vary but each specification system has a method for allowing these.

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P.E. Metallurgy, Plymouth Tube

 

[Erkamal]

Dear Sir/ Friends,

Thx a lot . I have been understood now.

Just for my clarity, I have attached the UNS N0 6625 material chemical composition .

Aa Per my understanding, for maximum condition alloy, we can add minimum value of alloy based on our experience and their effect on material behaviour. Right??? There is no international standard or some thumb rule right?......


Kamlesh

 

[arunmrao]

"Aa Per my understanding, for maximum condition alloy, we can add minimum value of alloy based on our experience and their effect on material behaviour. Right??? There is no international standard or some thumb rule right?......"

Why do you need to do it. Just specify the standard and leave it to the vendor to supply conforming to standards. If you attempt providing our own interpretation, in the event of a dispute, you will have little protection.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

If you look at your last 20-30 heats of 625 that you have used you will notice a few things.
1. Each mill balances the chemistry slightly differently, their targets as mil specific.
2. Mo being the most expensive element added will tend toward the low side of the range.
3. There will be certain patterns that everyone follows (elements to the low side or high side).

Some companies have their own specs, but in order for them to be usable they have to fall in the 'Goldilocks' zone, they have to be more restrictive than the UNS (or ASTM) and they still must allow what almost everyone is actually making.

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P.E. Metallurgy, Plymouth Tube

 

[mrfailure]

You also asked in your original question about tolerance.

Material specifications may have an allowable tolerances for delivered product that goes beyond the specification requirements. In order to know whether such tolerances apply, you have to first make sure you have the complete standard.

In your example of ASTM A105, the general requirements of the specification state "Product furnished to this specification shall conform to the requirements of Specification A961/A961M, including any supplementary requirements that are indicated in the purchase order." The allowable tolerance of the finished product for specified elements is defined in ASTM A961/A961M.

Your other example involved UNS N06625 (IN 625). UNS is strictly a specified composition range, and no product tolerance can be applied if that is the only specified requirement.

 

[NBrink]

If for whatever reason, you want to specify tighter tolerances within the alloy range, you're welcome to do that, just know that there will be a cost from the mill associated with doing so...

It's not especially uncommon (in refining at least) to specify 316 with min 2.5% Moly for example, when the spec is 2-3%.

 

[Erkamal]

Dear Friends,
Thanks a lot for giving so great information.

Kamlesh