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why mandate drop-weight test as long as impact test required?

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YuJie_PV

Mechanical
Jan 19, 2017
138
Dear all,

i am challenged by my manufacturer of boiler that as long as impact test performed for the material of shell, why still mandate drop-weight test.
BTW,the drum of boiler is constructed of low alloy steel with about 90mm thickness.

so i don't know how to answer the question but just say that the code mandates that.
i'd like to know what is the inherent difference between the two test, while both cares about toughness of steel?

Thanks so much

Jay
 
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The drop weight tear test provides a greater indication of toughness in thicker materials at very high cost. Charpy testing is a lower cost test method that provides quite good indication of toughness. In the many boiler steam drums that I have been involved, I have never seen a requirement for drop weight tear testing and ASME I certainly doesn't require such.
 
I used to do drop weight dynamic tear testing when I was working in railroad R&D. I always thought of it as a giant-size Charpy test. The advantage was little change of temperature due to the larger sample size in the time the sample was removed from the bath or furnace and the test. Dynamic tear was used in researhing heat treatment effects, and was also a requirement for many components.

I have also worked at facilities that had drop weight testers where a weight was dropped from a specified height, again both in the rail industry and also in a private industrial lab. I used those testers once or twice in each situations, but there was very little demand for those tests.
 
THanks for your reply, Weldstan and MRFAILURE.

i have another question. for instance, the steel is required to perform impact test at -20C。
if i specify the nil-ductility transition temperature of drop weight test 0C, is it total nonsense?
what do you think of it?

thanks in advance
 
Added cost with little gain, especially for a steam drum. Not sure why impacts at -20 C, as not required under ASME I but your Code of Construction may require such testing or owner/engineer may require.
 
Jay, your presentation of your question is confusing to me.

When you say nil-ductility transition temperature, do you really mean ductile-brittle transition temperature (i.e. where fracture is 50% ductile)? That would make better sense in the context of your question.​

Why are you supposed to come up with a transition temperature requirement? Wouldn't that be called out as one of your requirements​

Can you provide the exact wording of the requirements? I suspect something is getting lost in translation.​

Thanks.
 
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