NDT Acceptance Criteria for Bars and Forgings
NDT Acceptance Criteria for Bars and Forgings
(OP)
Good Afternoon,
I'm looking for standards that can be referenced to define NDT acceptance criteria for the following:
Rotating Shaft (Critical Component)
Material 4140
Test Specified - Ultrasonic Test and Liquid Penetrant Test
ASTM A788 (Standard Specification for Steel Forgings, General Requirements) does list criteria for UT, MPI, and LPT, however specifically states "Because of differences in manufacture, hot rolled, or hot rolled and cold finished bars (semi-finished or finished), billets or blooms are not considered to be forgings."
If the shaft was to be machined out of hot or colded rolled round bar, would this standard for acceptance criteria still be applicable or appropriate to apply? If not, are there any other ASTM standards that outline Classes of acceptance for bar (for UT, MPI, and LPT)? I have found an EN BS standard for UT of bars, but nothing from ASTM.
With regards to the A788 standard itself, what is the order of most stringent to least stringent UT level? I assume BR, DA, and then S.
Any comments with regards to what level's listed for acceptance are realistic?
Thanks
I'm looking for standards that can be referenced to define NDT acceptance criteria for the following:
Rotating Shaft (Critical Component)
Material 4140
Test Specified - Ultrasonic Test and Liquid Penetrant Test
ASTM A788 (Standard Specification for Steel Forgings, General Requirements) does list criteria for UT, MPI, and LPT, however specifically states "Because of differences in manufacture, hot rolled, or hot rolled and cold finished bars (semi-finished or finished), billets or blooms are not considered to be forgings."
If the shaft was to be machined out of hot or colded rolled round bar, would this standard for acceptance criteria still be applicable or appropriate to apply? If not, are there any other ASTM standards that outline Classes of acceptance for bar (for UT, MPI, and LPT)? I have found an EN BS standard for UT of bars, but nothing from ASTM.
With regards to the A788 standard itself, what is the order of most stringent to least stringent UT level? I assume BR, DA, and then S.
Any comments with regards to what level's listed for acceptance are realistic?
Thanks





RE: NDT Acceptance Criteria for Bars and Forgings
You have one of three choices - either develop your own acceptance criteria based on type and magnitude of service stresses and acceptable flaw size using proper design margin, or try to find an international standard for rotating equipment or try to locate AWS D14.6, Specification for Welding of Rotating Elements of Equipment. The acceptance criteria for welds will be as stringent as required for the base material.
RE: NDT Acceptance Criteria for Bars and Forgings
At this point I am going to call out UT and DPI - Class 3 for 100% of the shaft in accordance with BS EN 10308 and 10228. This is of course in absence of finding other relevant criteria.
Thanks
RE: NDT Acceptance Criteria for Bars and Forgings
The relatively easy solution is to have no linear indications permitted on the shaft surface using wet fluorescent MT or Liquid Penetrant testing – this would a one type of acceptance criteria.
Ultrasonic testing of forged shaft material is more complex because now you need to establish some threshold reporting criteria because with UT you are using shear wave to look for internal forging defects or inclusions. With a solid bore shaft I would use the UT shear wave method to ensure no planar internal defects - cracks or bursts.
RE: NDT Acceptance Criteria for Bars and Forgings
A much better criterion for MT would be "no indications over 1/8" in length". I would need to consult with a Level III in PT to come up with an appropriate criterion for that method. Having a minimum length gives the inspector the ability to ignore the small stuff, most of which are non-relevant indications.
For UT, "UT shear wave method to ensure no planer internal defect - cracks or bursts" is not an acceptance criteria, it is an inspection requirement.
The short answer is that you really need to consult with a Level III inspector to determine what inspection methods and procedures are appropriate to be able to locate the imperfections that you are trying to detect.
rp
RE: NDT Acceptance Criteria for Bars and Forgings
RE: NDT Acceptance Criteria for Bars and Forgings
I looked in my library and it appears I don't have a copy of D14.6. By the sounds of it I should consider purchasing a copy of it and will consider that tomorrow.
redpicker
Is there any relevance to my past post about bs en 10308 and 10228 Class III acceptance?
THanks
RE: NDT Acceptance Criteria for Bars and Forgings