NDE UT of Forged Ring (Hollow Forging), SA-388, Reference-Block Calibration, Change in Thickness

[PressEquip]

Hello,

Question: For a physical calibration standard/block for angle beam UT, how much of a change in thickness is allowed between the forging being UT inspected and the calibration standard/block?

We often buy forged rings that are then machined into body flanges.

One of out suppliers only offers them as-forged, so our shop does the rough machining and UT per SA-388 both: straight beam and angle beam examination.

For straight beam UT, per SA-388, para. 9.2.2.1 Back Reflection Technique (Back-Reflection Calibration Application to Forgings with Parallel Entry and Back Surfaces), we can simply use the rough forged rings to do the calibration. So this doesn't concern me.

What concerns me is the angle beam UT.

We do custom work so typically each forged ring has unique geometry. We don't make 100's or 1000's of parts of the same size, where creating a calibration block would make a lot of sense.

For angle beam UT, per SA-388, para. 9.3.3.1 Calibration with a Physical Notch, states: "A separate calibration standard may be used; however it shall have the same nominal chemistry, heat treatment and thickness as the forging it represents."

For a physical calibration standard/block for angle beam UT, how much of a change in thickness is allowed between the forging being UT inspected and the calibration standard/block?

For pipe, in ASME Sect. V, in Article 4, para. T-434.3 Piping Calibration Blocks, states: "...Thickness, T, shall be ±25% of the nominal thickness of the component to be examined. ...", and refers to figures T-434.3-1 and T-434.3-2. Obviously a forged ring isn't a pipe and this doesn't apply. But it shows how other pats of the code covering UT inspections allow for a percentage variation in thickness of a components before a calibration block is no longer considered representative of the component being inspected. Typically pipe has a mill tolerance of 12.5% on wall thickness so practically there needs to be some allowance for variation in wall thickness when doing UT inspection.

I'm trying to determine what the most efficient way is for us to complete this UT inspection.
- Each forged ring, order with extra material on the ID and OD so that a physical notch (approx. 1/4" deep) can be machined, per SA-388 para. 9.3.3.1 Calibration with a Physical Notch for Angle Beam Examination.

I'm wondering, if we should considering buying the software so we can do Distance Gain Size or Sensitivity (DGS) with our UT equipment which does not require a physical calibration.

Thanks in advance for responses!



A Fan of EngTips, share the knowledge

 

[EdStainless]

If it says the "same thickness" then I would say that it needs to be within the allowed tolerance for thickness.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[PressEquip]

Thanks EdStainless for the response

These forgings are for custom body flanges and other than the pressure vessel's designer's tolerance (typically the TEMA tolerance) on the finished machined body flanges; there isn't a ASME code standard tolerance. Also the forged rings are typically rough machined and then UT inspected; the forged rings still would have machining allowance on all the faces (making the rough machined forging thicker than finished machined). So in my mind, there isn't a clear ASME tolerance to use to answer the question of: For a physical calibration standard/block for angle beam UT, how much of a change in thickness is allowed between the forging being UT inspected and the calibration standard/block?

A Fan of EngTips, share the knowledge

 

[EdStainless]

How does your LVL III feel about this?
Ask them, check the procedure that you use.
Your cal procedure should call out dimensional limits.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[r6155]

Be careful. The UT must be carried out with certified personnel.

Regards

 

[JR97]

Pressequip,

As long as there isn't a significant difference in the rough machined and final machined thicknesses, the conservative approach is to cut the notches into one of each run of forgings at the rough machined thickness with the notch depth based on 3% of the final machined thickness. A small difference in notch thickness (3% rough vs 3% final) should have minimal affect on the calibration amplitude. I have used that approach with success as long as there isn't a significant amount of material coming off after rough machining.

JR97