Corrosion Testing of Duplex Tube-to-Tubesheet PQR

[minibenny]

I'm hoping someone can provide some help in regards to some issues we've been having with developing duplex tube-to-tubesheet strength weld procedures per ASME Sec. IX QW-193.

The material of the tubes and tubesheets are S31803/S32205 duplex. Tubes are 3/4" OD x 16 gauge. The tubes in the coupon were not expanded into the tubesheet.
We have no problem meeting the requirements of QW-193, but the issue is with meeting client requirements. It's common that duplex WPS' need to be supplemented with ASTM A923 Test Methods B and C, which is one of our client's requirements. However, due to the geometry of the tube-to-tubesheet coupon, Test Method B cannot be obtained, which the client is aware of. The experienced lab we generally send our PQR coupons to for testing and WPS development have been claiming the A923 Method C is not applicable to tube-to-tubesheet joints due to the type of specimen. Our client is insisting that the test can be accurately done on a tube-to-tubesheet coupon, and say they know it's been done before, but no guidance could be provided on specimen size and shape.

From discussions I've had with the lab, my understanding is that since the weld is only a partial penetration, and there is a gap between the tube OD and tubesheet hole ID, the A923-C corrosion test will provide inaccurate results. Apparently, there will be corrosion in the gap between the tube OD and tube ID, which will cause the specimen to fail the test even if there is no pitting or corrosion in the weld or HAZ.

I'm wondering if anyone can provide some feedback on experiences they may have had with A923 Test Method C on tube-to-tubesheet welds. Will expanding the tubes to the tubesheet make a positive difference? On successful tests, how were the tube-to-tubesheet weld specimens prepared?

 

[metengr]

The tube to tubesheet mock-up should have had the tubes roll expanded into the tubesheet. , since this is part of the production joint design. This is the approach I have seen over the years for tube to tubesheet PQR qualification. Roll expanding the tubes into the tubesheet mock-up results in direct metal to metal contact versus an existing gap, and corrosion testing will not be adversely affected.

 

[EdStainless]

You need to section out just he portion of interest for a sample.
The surfaces must be freshly ground for a 923 test.
You can seal the back side with wax so that you don't get crevice corrosion.

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Plymouth Tube