Vendor Claiming No NDT Necessary

[TiCl4]

We are having a tank manufacturer build several API 620 tanks. The vendor is claiming that they are only required to complete a visual inspection and hydrotrest. I argue that, under section 7.17.2.1, spot radiography is required in all cases unless 100% radiography is required. In our case, we don’t meet the requirements for 100% radiography, but still need spot check x-ray.

Am I missing something?

 

[JStephen]

Refer to Table 5-2, joint efficiencies.
The way I read that, the first two lines require either spot or full radiography for shell welds at 85% and 100% joint efficiency.
The next three lines are "dash" (no radiography), spot, or full, at 70%/85%/100% but those are for "Roofs above liquid level" only, not for shell welds.
The lines don't line up as printed, so it's sort of confusing, but I believe the intent is that all shells are either spot or full radiographed.

 

[TiCl4]

JStephen,

Right. The section I referenced specifically mentions that roof seams could be excluded via Table 5-2. I have seen no such reference to the shell joints.

 

[HTURKAK]

I agree with you..and think that, it is clearly stated in ( 7.17.2 Spot Examination of Welded Joints
7.17.2.1 For all butt-welded main joints (see 5.26.5.2) that are not completely examined, spot examination is
mandatory and shall be done according to the procedure and standards of 7.15.6 and 7.17.4, except roof joints exempted by Table 5-2. )

And Table 5-2 Maximum Allowable Efficiencies for Arc-welded Joints ; for all double-welded joints, ( except for roofs
above liquid level ) there are two joint efficiencies and for Spot radiography 85 %.

If the tank-wall thicknesses at the joint exceed 11/4 in. and the joint is subjected to tension stress greater than 0.1 times the tensile strength; Full examination is mandatory. refer to Appendix P NDE and Testing Requirements for Summary.

You did not define the tanks ..You may look to Figure Q-2 in case of app. Q tanks and Figure R-2 for app. R tanks..

 

[NDT3RICH]

There is a lot of NDT required when building a 620 tank! Please refer to Appendix P. It sounds like your vendor has underbid the job and does not want to follow the standard.

 

[TiCl4]

As an update to this, we verified my understanding with a certified API inspector. He confirmed the radiography was required, and that my interpretation was correct. The vendor performed the required radiography. It turned out that 1/3rd of all shots had defects (fusion defects) and had to be repaired. The time it took for repair delayed a major installation we had planned, and will end up costing us significantly.

I think I have learned my lesson on assuming a tank vendor will be fluent in all the required aspects of a particular code...

 

[david339933]

And of course they did the extra shots required when defects were found??

 

[TiCl4]

Yes, the API inspector that was doing the 3rd party inspection did the shots on either side of the defect to confirm the extent of the defect. The defects are being ground out, re-welded, and will be re-radiographied when complete.

 

[IFRs]

Given the 33% rejection rate, I'd consider 100% RT as a possibly prudent step towards ensuring integrity. API 620: "The rejected weld shall be removed and the joint shall be rewelded, or at the Manufacturer’s option, the entire unit of weld represented shall be completely examined and only the defective welding need be corrected." See section 7.17.4 (from an old edition, this may have changed since 2014).