Maximum Deviation/ Tolerance in Mechanical Properties ? 1

[Rizkyffq]

Hi All,

May someone help me, i already searched in everywhere but i still cannot get the answer.
Is there any standards that stated about Maximum Deviation/Tolerance in Mechanical Properties ?

So the case is between Mill Certificate of material and Standard are having difference value between them, but the difference is very very little is like between "450 MPa and 448 MPa".
So actually we want to accept it because the deviation is very little, but we need a legal statement that stated the range tolerance of deviation.

Before many thanks guys.

 

[ulyssess]

I don't know which type of material is concerned, but for carbon steel plate see ASME SA20/SA20M subclause 10.3

"10.3 Rounding Procedures—For purposes of determining conformance with the applicable product specification, a calculated value shall be rounded to the nearest 1 ksi [5 MPa] for tensile and yield strengths, and to the nearest unit in the right-hand place of figures used in expressing the limiting value for other values, in accordance with the rounding method given in Practice E29."

Please note that discussion often arise due to unit-dependent different minimum values in ASME.
ASME SA20/SA20M subclause 1.5

"The values stated in either inch-pound units or SI Units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification."

E.g.: ASME SA 516-65 has a minimum tensile strength of 65 ksi when delivered to inch-pound units and 450 MPa when delivered to metric units. Or 65 ksi is exactly 448 MPa. So if a tensile strength is measured 448 MPa, the plate can be delivered when certified 65 ksi, but is not conform to specification if certified as SA 516 grade 450 with a value of 448 MPa.

 

Not sure what the question is here.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[mfgenggear]

most specifications will specify tolerances, AMS , QQ-X-XXX ect

 

[Rizkyffq]

Thanks ulyssess for the information.
So we have a legal statement from a standard that those comparison between mill certf and material spec are conformance.

 

[MintJulep]

There is a thing called "engineering judgement" which is what you should be using in cases like this.

 

[kingnero]

He's asking for a legal document, so I'm assuming the context but if the client has a "spec is spec" mindset, your engineering judgement is basically worthless. Regrettably.

 

[MintJulep]

I read it as he is trying to avoid being an engineer by hiding behind a piece of paper. But maybe I'm just cynical.

 

[EdStainless]

For example if the ordered sped is A20 as in Ulyssess example, if it was simply ordered to A20 the min strength must not be less than 65ksi. If it was ordered to A20M then the strength must not be below 450MPa.
The spec is the legal basis for the contract.
People that play mix and match with units are playing with trouble.

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[kingnero]

I read it as he is trying to avoid being an engineer by hiding behind a piece of paper.

True, but either him or the client. I was giving him the benefit of the doubt! One of them certainly is.

 

[mfgenggear]

actually it starts with the P.O., the engineering drawing and the specifications on that drawing.
whether by the designer or the manufacture, be precise

 

[IRstuff]

It seems to me to be a simple question and answer. If they want to accept non-conforming material, then they need to go back to the engineer who specified the material to write up a waiver stating that the non-conforming material still has sufficient margin to do the job.

TTFN (ta ta for now)
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[EdStainless]

In ASTM or ASME there is no room for exception. If it doesn't meet the spec it cannot be certified to it. Period.
So if they want material with a test report but no spec on the CMTR, then fine.
I used to have a line in my spec that said 'all measurements must be reported in the units of the actual measurement, conversions may be noted in parenthesis'. I was sick of hardness conversions that were so far off as to not be usable.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[IRstuff]

Like I implied, it would still be non-conforming, and essentially, the engineer would waive his requirement for ASTM conforming material, based on his assessment of whether there's sufficient margin, if any. Obviously, he would be in uncharted territory, unless he finds some other material spec that looks like the non-conforming material to get its mechanical properties.

TTFN (ta ta for now)
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[Tmoose]

What material standard are you using ?
As said by others, many ASTM materials have ranges, or minimums.
Is your question about a material that tested 2 MPS below the minimum or over the maximum ?

Single number values are so unrealistic as to reflect badly on the user's and especially the originator's parents.

 

[mrfailure]

From a test lab perspective: Conformance is based on the precision of the specification so, for example, a test result of 79.9 ksi will be rounded to 80 ksi if specification is something like 70 ksi minimum, but it won't be rounded if the specification instead reads 70.0 minimum. Rounding is performed per ASTM E29 as ulysses noted. Also as noted, mechanical properties do not usually have an allowable tolerance so conformance is absolute.