Equivalent diameter in tensile test

• Sep 29, 2022

• #2

TugboatEng

Marine/Ocean

Nov 1, 2015

11,839

Equivalent diameter usually refers to the flow area of a tube. For a circular tube, the equivalent diameter will be equal to the ID.

 

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• Sep 29, 2022

• Thread starter
• #3

isoca

Materials

Mar 16, 2008

58

Thanks for the answer, but I have a question.
If the equivalent diameter is related to flow area (cross section?), where does it come from that it is equal to the ID? As far as I understand, the ASTM E8M indicates that the gauge length must be equal to 5D where D is the external diameter.

 

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• Sep 29, 2022

• #4

TugboatEng

Marine/Ocean

Nov 1, 2015

11,839

I think your customer used the wrong terminology and this should be clarified with the customer. Equivalent and external seem like easy enough words to swap if English isn't a first language.

 

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• Sep 29, 2022

• #5

EdStainless

Materials

May 20, 2004

16,283

In the US people use 2" or 4D (outside) for tube GL.
In Europe it is more common to use 5D.
I have seen both OD and mean D used in the GL calculation.
At the end of the day it doesn't matter.
Annealed 316L will be up over 50% elong however they measure it.
Strain rate matters more.

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P.E. Metallurgy, consulting work welcomed

 

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• Oct 4, 2022

• #6

WKTaylor

Well-known member

Sep 24, 2001

4,181

WHAT 316L material-tube specification, WHAT strain hardness and WHAT wall thickness?

Is this a structural tube or a fluid-flow ['hydraulic' quality] tube?

Regards, Wil Taylor
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• Oct 5, 2022

• Thread starter
• #7

isoca

Materials

Mar 16, 2008

58

The tube is an ASTM A213. We have a lot of experience in manufacturing this type of tubes, however in this case the client requests that for the tensile test the elongation shall be taken using a gauge length equal to 5D where D is the equivalent diameter. What is not clear to me is the meaning of "equivalent diameter", that's all.
Thank you

 

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• Oct 5, 2022

• #8

EdStainless

Materials

May 20, 2004

16,283

The client doesn't know themselves.
I would use the OD.
And you need to also report the value with a 2" GL in order to comply with A213

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

 

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• Oct 6, 2022

• #9

MagBen

Materials

Jun 7, 2012

728

Theoretically, equivalent diameter = Squad (OD^2-ID^2)

Practically, you can use equivalent diameter = (OD+ID)/2. Or, simply use equivalent diameter = OD

Intrinsically, all probably donot matter much, as Ed pointed out, since 316 material would have a large elongation value (unless the deformation rate >95% during manufacturing).

The key is to clarify with the customer.

 

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• Oct 6, 2022

• Thread starter
• #10

isoca

Materials

Mar 16, 2008

58

Ok thanks for the information. Obviously it is something that I asked the client, but sometimes the answers tend to come too late.

 

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