NDE and MPI 1

[zulsaid]

Dear All,

Is it necessary to do NDE or MPI for final machining component? Is there any possiblity that material can be cracked or defect after machining?

If any defect/crack is because of raw material or procedure of machining problem?

Thanks

 

[arunmrao]

It is best to perform NDT check at the raw material stage,thus avoiding wastage at and heart burns (in my case high BP) at the final stage of inspection, It will minimise agonies to say the least.

Machining as such will not introduce defects in the raw material,excepting build up of internal stresses ( probably if due care is not taken,).

If you mention the alloy being machined and the machining process,better information can be available.

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________

 

[zulsaid]

Dear arunmrao,

That's mean once we already present the test at the raw material, so we dont need to do test to the machining product.

Thanks

 

[SJones]

What does the purchaser require? What NDT would be performed on the starting material?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[zulsaid]

The purchaser request for MPI for pressure containing part like ball, body and closure but doesn't mention which stage need to do test either at raw material or final machining.

Currently our forging supplier do UT test for the raw forging material(per heat no.) then once finish machining we do MPI test to the finish product.

Do we still need to do MPI for the final machining even we already check the raw material?

Is there any possiblity the material crack due to during machining job?

 

[arunmrao]

Now you are disclosing the parts as pressure parts. In this case,the ultimate test of pressure testing will have to be done before certifying it as acceptable.

Please also remember that no upgradation will be permitted if the parts leak under pressure test.

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________

 

[JR97]

MPI is a surface inspection; particularly if a yoke is used. If a yoke was used in a rough machined condition, or if more than about 1/16" of material was removed, all you tested was the chips you removed. MPI and/or Liquid penetrant should be done on the final surface. You may want to continue, on an informational basis, the MPI on the raw material to disclose if there is a major problem with the material before you invest in the machining. UT is a volumetric inspection so the stage of manufacturing is not as critical. Generally UT can be done anytime after heat treatment.

JR97

 

[SJones]

Try to think it through. How reliable is the forging supplier's UT? Have you ever found a defect by MT even though the material has been subjected to UT? What is the application of the items? What defects can you expect and will they be a critical size in service? Will they grow to a critical size in service? What are the consequences of the failure both to the user and you as the supplier? What does the customer really want if you go back and ask? Having determined answers to the foregoing, what is the monetary value of omitting MT? More importantly, what have you offered to do and the customer has accepted and are you looking for a way to change that arrangement?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[tgmcg]

Yes. Do not skip performing NDE after finish machining. Prior inspections can and do miss rejectable defects.

Ask me how i know....

 

[arunmrao]

tgmcg : how?

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________

 

[tgmcg]

Today we rejected two 1400 HP turbine rotors on tight delivery schedule because post-machining MPI turned up many dozens of linear indications on the smaller diameter sections of the rotor. The forgings were previously inspected by UT and MP. I do not understand why prior NDE missed so many defects.

 

[arunmrao]

tgmcg
thanks for sharing your experience. No words can compensate for your pain and frustration. I have marked your thread and sent them to a few friends of mine.

Who did the NDE? Was it by an independent agency or used vendor's facility?



I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________

 

[zulsaid]

tgmcg,

I also just experienced it last 3 weeks, which after machine we found porosity causing 1 heat was rejected.

During UT not found any defect.

 

[tgmcg]

Thank you all for the supportive words. We absolutely need to identify an appropriate NDE protocol to identify such defects earlier in the process.

Is improved NDE the solution, or perhaps better oversight of the forge and ingot manufacturing procedures? I'm not sure what the limits of current UT practice are.

 

[hogan666]

When performing UT of forgings you need to have an appropriate procedure. A technique that is repeatable on parts with known defects or a mock up. Without this there is a good chance you can miss indications. UT (longitudinal) and MT (WFMT) when performed correctly should find any discontinuities in your forging. Consult a level III.

 

[mfgenggear]

after heat treat if possible do in process inspection during machining.

depending on the type of heat treat and material,
defects from machining can be induced. Normally from grinding. Yes this is the result of wrong grinding wheels or procedure or both.

forgings or castings but also wrought material will crack during heat treat if not properly processed or it can open up defects not detected from previous NDT.

I have experienced UT not detecting fine defects.
you need an example\Test piece for the technicians to qualify their test.
so this is where mag & penetrant is useful.
picks up fine defects on the surface