what is meant by the minimum elongation required in astm a182/a 182m -

[etrobal]

sir:

Table 3, Tensile and Hardness Requirements, page 9 of the ASTM STD A182/A 182M - 99, Standard Specification for Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings and Valves and Parts for High-Temperature Service provides among other things, the Elongation in percent minimum.

We had a valve stem specified as F6a Class 4 destructively tested to check its properties under this Table 3 of the ASTM standard.

The elongation test result came out as 24% while the minimum required under Table 3 is 12%. Does this mean that the valve stem passed the elongation requirement of the Standard?

The valve stem failed in all the minimum required under tensile, yield, reduction in area.

i would like to solicit some advice regarding this elongation minimum as per Table 3. or should this be elongation maximum?

what is meant by the term in table 3 as "elongation in 2 in. (50mm) or 4D, min,%"?

thank you very much.

 

[SJones]

ASTM E6 would be the document to consult to learn of mechanical testing definitions. No doubt, some kind person on here will type out verbatim what it says for you. If there is a minimum specified and the the value obtained exceeds that specified minimum then it can be stated that the elongation meets the requirements of the specification.

Elongation is a means of imposing a required minimum level of ductility to match the minimum strength requirements: generally, it would not be useful to have a strong material that is unacceptably brittle. The converse is also generally true which may explain why the excellent ductility value recorded in your test coincided with insufficent strength.

The elongation value is generally expressed in terms of the percentage increase over the original 'gauge length' that was used as the datum at the start of the test.

Steve Jones
Materials & Corrosion Engineer

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

 

[Ron]

etrobal...it is a minimum. The reason for it is to make sure the part has adequate ductility. Low elongation would imply a potentially brittle material, more sensitive to some types of failures.

It sounds like your stem material is relatively soft and weak.

 

[etrobal]

thanks sir jones, sir ron.

i did read ASTM E6 and there were for discussion items there on elongation. were these items meant to confuse rather than provide a clear definition of elongation?

further to the destructive test done by a reputable third party testing agency, the test result was questioned by the manufacturer as the minimum parallel length required by A370, Test Methods and definitions for Mechanical Testing of Steel Products, under Figure 4, referenced as 'A', is 45mm, while the test specimen prepared was at 40mm.

am i correct in emphasizing that the parallel length has no bearing to the test and it is the gage length, which was followed, that should be taken into account?

again, many thanks indeed.