B31.8 and API 5L Annex G CVN vs DWT 3

[AgsMyDude]

I am reviewing a specification for a gas pipeline (material API 5L PSL2) with a minimum temperature of -50F. According to B31.8, this triggers Annex G of API 5L. I am really struggling to sort the actual requirements of CVN and/or DWT testing.
- My understanding is that shear area is calculated from DWT and absorbed energy from the charpy (CVN) test. Is that correct?
- If the above is true, how is the shear area requirement (85%) of G.3.1 determined for line sizes </=20 in since the DWT test is apparently not applicable in that range?
- What is meant by a full-size test piece? My understanding is that CVN tests are performed on 10mmx10mmx55mm samples. Is this applicable to DWT?
- I assume the greater value of API 5L Table 8 or Annex G should be used (since we specifying PSL2 pipe) for minimum CVN energy.

Thanks in advance

 

[SJones]

- Shear area can be derived from both types of test as both will generate fracture surfaces
- The restriction to 20-inch for DWTT is a false restriction, probably based on pipe mill whining. DWTT can be achieved on smaller diameters. The UK and Australia require it from 12-inch.
- Correct the 10 x 10 x 55 Charpy. DWTT will be on full thickness test pieces, and have its own test piece dimensional requirements
- The required CV energy will be driven by the greater of the brittle fracture criteria of Table 8 versus the criteria derived from your ductile fracture arrest study.


Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[AgsMyDude]

Thanks a bunch Steve, very helpful.

I assume DWTT also produces energy values? Equations 1 and 2 in para 841.1.2 of B31.8 note the calculated CVN values as being "full size Charpy V-notch absorbed energy". That would indicate to me that these are in fact DWTT, not charpy tests. Annex G also makes references to CVN for full-size test pieces.

It is also interesting to me that Annex G specifies its methodology as being applicable to buried, welded pipe whereas B31.8 makes no such distinction.

Thanks again

 

[SJones]

Confusion is understandable since 31.8 has pointed you to a ductile fracture arrest consideration when it is trying to address brittle fracture. The DWTT will not give you energy values unless instrumented equipment is used, and the values should be massive compared to the criteria that you are reviewing. Such equipment is not alluded to in API Spec 5L. The "full size" is the full, standard Charpy test piece size.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[akpipelineengr]

full size Charpy V-notch absorbed energy

This statement does refer to CVN testing on full size coupons, i.e., 10mm x 10mm, as opposed to subsize coupons, which are permitted when the pipe isn't large enough to produce full size ones. The absorbed energy from subsize specimens can be converted to an equivalent full size energy value for comparison. Have a look at ASTM A370.

 

[AgsMyDude]

Thanks all,

Not being familiar with ASTM A370, it was not clear to me that full size specimen =/= pipe body. That clears it up.