CVN Impact Test 1

[River7]

Why do we need to do CVN impact test at –46 degrees Celsius to qualify a WPS?
Is it a contractor requirement or ASME Code or AWS D1.1?

 

[stanweld]

Minimum design temperatures, usually defined by the Engineer or Owner, together with the governing design Code or Jurisdiction determine the need for Impact Test Qualification of Welding Procedures. You need to provide more information regarding what you are welding and the design requirements in order to provide a more detailed discussion.

 

[River7]

Thanks stanweld for your respond.
My question is just a general one. I mean, is there anywhere at AWS D1.1 or ASME Code, refering to CVN impact test at -46 degress Celsius?
Or it's just a contractor/design requirement? and why -46 degrees?
Thanks in advance for your help.

 

[grampi1]

-45C would qualify standard ASTM impact tested P1 materials, (A333 Gr 6, A350 LF2, etc) making the PQR as applicable as possible for P1.

 

[HgTX]

I couldn't find anything in D1.1 but that's not to say it wasn't some other number affected by some adjustment factor.

This is probably a really stupid question (what I'm best at), but why not just ask the specifier why they specified that?

Hg

 

[VeryPicky]

I know we are looking at AWS D1.1 but I don't have a copy handy to check, so I will quote some ideas from the codes I currently work with.

If you design a structure for climatic area of -46°C and up it might be a reason for that requirement.
ASME VIII (and AWS D1.1 too) being an imperial units code uses specific temperature values in °F.

Some materials are prequalified for use at -50°F (-45.5°C) as per ASME VIII Div 1 UCS 66. The impact exemption curves are also based on round °F values. These temperature values are customary thresholds for impact testing temperatures.
Your -45 or -46°C comes directly from calculation from °F.

As HgTX rightly says "if in doubt - ask".
And by the way: couldn't you use prequalified procedures?

 

[Carburize]

All Charpy test requirements are arbitrary, both the absorbed energy and the test temperature. The test bears no relationship to any actual failure mechanism and is only a very qualitative control test. During the last 50 years or so a number of certification societies have settled on numbers that give them a warm and fuzzy feeling - don't try and understand the science behind the requirements - there isn't any!

 

[stanweld]

River7
JacekM is right on with regard to the -46C CVN test origins that you have described; however, the minimum design metal temperature (MDMT)is specified by the Engineer/Owner. When the Engineer/Owner defines an MDMT of -46C for items fabricated from ferritic steels, ASME Section VIII, B31.3, etc. requires the welding procedure to be impact test qualified at that temperature.

 

[AJohnson]

ASM handbook Volume 8, Mechanical Testing, has a good history section on how CVN testing came into being, its limitations, and most importantly, its overall purpose, which is to define the temperature range of transition from ductile-to-brittle fracture. These two sentences seem particularly relevant. "Much Charpy impact testing is done at temperatures lower than those commonly designated as room temperature. Of these low-temperature tests, the majority are made between room temperature and -46 °C (-50 °F), because it is within this range that most ductile-to-brittle transition temperatures occur."



Andy