Impact testing " TEST TEMPERATURE" for PQR specimen

[Sooraj Sucheendran]

Hi All,

This is a basic question but still needs an answer for a beginner like me.

Question is regarding Impact testing " TEST TEMPERATURE".

1) how do we decide at what temperature the test should be done for a particular base metal for PQR tests?
Is there any factor that will be considered from the filler metal property( weld metal)?

We have two types of temperatures available.
1. Service temperature/design temperature (MDMT) that we get from piping specification/ designer( or any other temperature data required for this?)
2. Minimum Temperature from ASME B31.3 Table A (sixth column) and Fig 323.2.2A showing curves which determine minimum temperature at which impact testing is not required.
For the time being other relaxation on temperature by stress ratio and other factors can be skipped.

Suppose by calculations we found out that impact testing is required since minimum design temperature falls below minimum temperature of Table A, then at which TEMPERATURE the specimens should be prepared for IMPACT TEST? is it at the same minimum design temperature or some other temperature?
Reply can be based on B31.3 or Sec VIII Div i.

 

[david339933]

UG-84: Impact temperature shall not be warmer than the MDMT.
B31.3: 323.3.4 says the same.

 

[Sooraj Sucheendran]

Thank you for your reply Mr. David.

I have one more query,
That is our service line has a thickness of 6mm and design temperature (MDMT) is -23°C and minimum temperature calculated as per curve B is -20°C which demands impact testing., but my PQR test piece for the same base metal has a thickness 15mm or more which can elevate our minimum temperature in the calculation as per CURVES in fig 323.2.2A. Let's say this situation gives relaxation from impact testing because of the thickness.( shape/slope of the curves are increasing with thickness and vice versa)

So in this case should I consider 6mm or the PQR specimen thickness (15mm) for calculating the minimum temperature?

 

[david339933]

Curve B is -20F not C. That is -29C. No impact testing should be required.

But to answer you question:
The test temperature is the MDMT or colder, regardless of thickness. The thickness of the PQR coupon will determine the thickness qualified, but not the test temperature. There are exceptions for sub-size specimens, but I will leave that alone as you state you are a newbie.

 

[Sooraj Sucheendran]

again thank you for your prompt reply,

please note that second question was entirely different from the first.There is no any concern of "test temperature" which was already clear from your first reply.

Also please note that curve B have minimum temperature range from -28.9°C to higher as per table 323.2.2A. of B313.3-2020 varies with the thickness so at 15.9mm the minimum temperature is -16.7°C and at 6.4mm the minimum temperature is -28.9°C( this is my understanding of the tables and graph)

I have used the word "Suppose" to denote that its not a real situation. But such a situation can happen. please look at the question only considering the thickness that I have mentioned. Whether we have to take design thickness or the PQR specimen thickness to decide whether we need impact test or not? suppose my PQR specimen thickness is different from design thickness.

let me elaborate a bit more,as the initial step to decide whether we need impact test or not, we need two parameters for calculating minimum temperature , one is the curve type and other is thickness, so my question is regarding the thickness only.

also please note I am not asking about the range of thickness qualified.

Now you may please read my second question again, I am afraid whether my english is bad!!

 

[david339933]

You need to qualify your welding procedure to cover what will be done in production. Therefore your PQR must cover the MDMT of the actual thickness used in production. The tables give exemption temperatures for different thicknesses. For 6mm you go to the table and see that for a Curve B material it is exempt from impact testing at a minimum design temperature of -29C and warmer. PQR thickness plays no part here.

Now going to Sec. IX, I refer you to QW-403.6. This states that if you do a PQR with a coupon of 15mm as you stated above, then the qualified thickness for your WPS is 15mm and greater. You would not be able to weld 6mm with this WPS. You have to do a PQR on 6mm (1/4").

So you see the PQR thickness is not arbitrarily selected, it is selected based on what you have to weld in production. Doing a PQR on 15mm when you need to weld 6mm is no good.

 

[Sooraj Sucheendran]

Thank you Mr.David for your reply with xtra infos...

 

[FacEngrPE]

Impact testing " TEST TEMPERATURE" for PQR specimen needing to be lower than service temperature is a hard learned lesson.

Metallurgy & Materials Engineering , Liberty Ship Failures