Scale consideration with ultrasonic wall thickness testing

[timsch]

I'm running calculations to re-rate our carbon steel hydrotest chambers. I have UT wall thickness measurements. These chambers are very long (4 to 5" pipe, 100' long), so any scale that might be on the ID of the chambers was not removed. Would scale throw off the measurements, or would the scale be too discontinuous from the uncorroded metal to affect the readings?

 

[Andrew ONeill]

In my experience, not a problem, extensive experience with hard slurry like scales that form inside pipes, sometimes several inch's thick. This is assuming you are measuring from the outside. If you are measuring from the inside, it will be a problem.

 

[timsch]

In my experience, not a problem, extensive experience with hard slurry like scales that form inside pipes, sometimes several inch's thick. This is assuming you are measuring from the outside. If you are measuring from the inside, it will be a problem.

Thanks for the response. We're measuring from the outside.

 

[LittleInch]

Re rate sounds interesting.

Unless you have a full scale body map, your potential errors in missing a patch of corroded metal are far higher than the odd mm or so that your U/T machine misses.

what sort of U/t coverage are you planning?

 

[r6155]

Please take care of the calibration of the instrument and use qualified personnel.

 

[timsch]

Re rate sounds interesting.

Unless you have a full scale body map, your potential errors in missing a patch of corroded metal are far higher than the odd mm or so that your U/T machine misses.

what sort of U/t coverage are you planning?

We're taking 4 measurements @ 90deg every 3 feet, totaling 168 points (chambers are actually over 100' long). Statistically, I think we should be fairly confident that we have a pretty good picture, but I agree that we likely don't have the absolute minimum thickness. My calculations are conservative so there is wiggle room already there. Your prodding did make me consider that they likely do not empty the chamber and that I should look to see where the water line may tend to be and do a closer inspection in that area, so thanks for that.
.

 

[LittleInch]

Well I guess you will need to hydrotest your chamber to 1.5? times it's MAOP or mx test pressure for whatever it is that you put inside this thing.

For me that's nowhere near enough data points. I would want ones every 6 inches and at least eight around the circ to catch areas of corrosion big enough to be an issue.

Or just build another one from new pipe....

 

[timsch]

Well I guess you will need to hydrotest your chamber to 1.5? times it's MAOP or mx test pressure for whatever it is that you put inside this thing.

For me that's nowhere near enough data points. I would want ones every 6 inches and at least eight around the circ to catch areas of corrosion big enough to be an issue.

Or just build another one from new pipe....

We will test it to 1.5 times its MAOP. I will keep your other recommendations in mind. Thanks for the responses - much appreciated.

 

[timsch]

Please take care of the calibration of the instrument and use qualified personnel.

3rd party inspection service has done the measurements.