Occasional Elongation Oddities
Hi all, hopefully this an easy one and I’m left feeling dumb.
I work in a mechanical test lab where it’s very common for us to run a tensile test to verify incoming properties on our vendors pipe/plate. Got a number of vendors from just about everywhere and a range of carbon, low alloy, stainless, and nickel-based alloys. Sometimes the material comes in raw/as-rolled and sometimes it’s heat treated from the mill prior to shipment.
The samples we use have minimal/zero cold work and are not torch cut. We get a rough piece of the pipe/plate cut out then get it machined to the standard A370 strip-type specimens with a 2in gauge length and 1/2in width for the reduced section.
We generally get good matches on yield and tensile strengths, but occasionally our measured elongation is noticeably lower than the mill’s values. For example, if we get a low alloy pipe whose elongation is reported as 42% from the mill, sometimes we’ll get results closer to 34% or somewhere in that neighborhood. Other times on other tests we’ll get much closer matches.
Can someone chime in on where this occasional difference may be coming from? We are testing in the same direction (longitudinal) and are using the same strip-type samples as the mill and I’ve seen this behavior on numerous grades, so I tend to think it’s something in our testing process.
Thanks all,