Criteria for hot tensile test 2

[PAN]

I found the related thread in thread794-103286 .
However, I still do not know the criteria for hot tensile test. Please comment for my opinion below.
- Should we follow mill's recommendation for all cases? What is the basis from mill's comment?
- I understand that the ASME allowable stress shall be less than yield strength at elevated temperature. Therefore, the yield strength from hot tensile test should not be less than yield strength from the ASME Table. - If we do not have the criteria for hot tensile test, why should we perform hot tensile test?

 

[metengr]

PAN;
What are your specific concerns related to performing an elevated temperature tensile test? Your post seems confusing. ASME has notes that indicate mill tests may show some variability in comparison to minimum published values.

 

[PAN]

metengr,
In my case, there are 2 materials (SA 542-D Cl.4a and SA 387-22 Cl.2). Hot tensile test is a requirement without acceptable criteria.

I agree that ASME allow the variability in comparison to minimum published values. However, I do not know what is the maximum variation (-10%, -15% or more) that we can accept? Please comment.

 

[SJones]

What standard or specification is dictating that you perform an elevated temperature tensile test? If there is no stated acceptance criteria, could it be that the test is being demanded for information only?

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[metengr]

PAN;
The client's specification must have invoked a Supplementary requirement for SA-387, which is S7, a High Temperature Tension Test. This is their right to do so.

Now, if you intend to evaluate the high temperature tensile test results go see the Notes in Table Y-1 of ASME B&PV Code, Section II, Part D. This table contains published minimum yield strength tensile values for various Code approved materials. A similar Table exists for tensile strength values, as well.

Look at Note (b) at the end of the Table Y-1. It mentions....to summarize (briefly) the Code Committees of Section I, III and VIII do not require elevated temperature testing of production materials used in Code components. This is important because ASME does not and will not recommend any comparison of actual test values with published minimum values in Table Y-1. The note continues that if the test results fall below the minimum values by a large (my words would imply significant) amount, a retest or further investigation should be performed.

Your client can do one of two things, they can evaluate the test values with published minimum values in Table Y-1 and decide on their own if the test values fall "significantly" below these values. Keep in mind that you are dealing with statistical populations for the published values from ASME B&PV Code committee Section II and using the results from only a few tests. The second option is to discuss the tensile results with the mill and decide if this is a heat of material statistically falls below a reasonable minimum acceptance level.

 

[bmoorthy]

But what is the purpose of asking hot tensile test. under what circustances one demands hot tensile.

If Client wants for information purpose only what purpose does the information serve? There has to be some rationale for asking such a test.

Can some one throw some light on need for such a requirement

 

[metengr]

Yes. The client would want to assure minimum thru thickness mechanical properties for heavy wall plate thicknesses.

 

[PAN]

Sjones,
I intend to refer test method in ASTM E 21.

You may be right. The mill propose that test result should be for information only.

metengr,
I still worry that we cannot assure anything because of no acceptance criteria.

In my opinion, I will keep the minimum yield strength from Table Y-1. I will allow the lower tensile strength from Table U. This may be -10% or more. I belive that the material must hav a yield point that is sufficiently far from the ultimate strength. However, I still cannot find the reasonable relationship between them.

 

[SJones]

I wasn't inquiring about the actual test specification to be employed, it was about what element of the purchase order dictates that the testing be performed in the first place. E21 is as good as any other. I'm wondering if your client is trying a bit of reverse engineering: they are not quite sure of the operating and design conditions and are taking a bit of a flyer; because of this uncertainty it may be necessary to do a fitness for service analysis; naturally, it would be ideal to do the FFS up front and thereby set criteria for whatever testing is necessary, but they haven't had the time so the best they can do is ask for the testing now so that the data is available later on to do the FFS. In the meantime, they keep their fingers crossed. Of course, I could be wrong!

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/