Defects in Pipe 1

[enginerding]

I posted this earlier in the "Structural Other Topics Forum", but I think maybe this is a better location for this discussion...

I was using a t-mic wall thickness gauge to verify the wall thickness of column pipes that were delivered in the field. The pipe was either API 5L-X42 or ASTM A252 Gr. C pipe, 66"Øx0.875". This section of pipe is 40'-0" long and is made up of five 8'-0" long cans. The pipe was rolled and welded, not spiral welded pipe. I checked the thickness of each can as I went down and all of them were coming out at roughly 0.880" thick. The last can measured 0.413". I moved the mic over about 2" and it read 0.88". I started checking a bigger area around this initial bad reading and found a somewhat random spattering of good and no good readings. The measured thickness is 7/8"; there is no pitting.

The gauge was consistently reading bad where the bad readings were found and consistently reading good where the good readings were found. There were a couple of spots where the t-mic provided a good reading with the mic axis running one direction and a bad reading with the mic axis perpendicular to the first spot. Maybe the edge of an internal imperfection?

All the bad readings ranged from .390" to .430" – right about half the thickness. We cut out a portion of the pipe so we could see if we could find some cracks or delamination, but it was impossible to see anything on the torch-cut edges. Oddly enough, even though the steel in the coupon tested no good in the pipe, after it was cut out, it tested fine everywhere.

I don't know what to think about this. The bad spots seem to be so small that they probably won't cause a problem, but so many of the locations tested badly. Because the bad readings are all roughly the same, I think the delamination, cracks, or other imperfections don't run through the thickness, but rather parallel the surface of the steel. Does this seem reasonable?

Have you had a problem similar to this before? Is this a common problem? Do you have any suggestions of testing we should perform, or questions I should ask the pipe supplier?

 

[Ron]

It is probably a lamination. Grind the flame-cut edges, sand them as flat as possible, and then etch the faces with hot muriatic acid. This should show the lamination.

 

[eyec]

another suggestion is to use a cut off saw and etch that edge, less sanding and disruption of any possible lamination

Steven C
Senior Member
ThirdPartyInspections.com

 

[metengr]

You can also have shear wave ultrasonic testing performed to confirm the size and depth of the laminations.

 

[enginerding]

Would the heat from the torch bond the laminations back together again? The same section of pipe that showed up bad on the pipe tested fine after it was cut from the pipe.

 

[JR97]

Concur with the ultrasonic testing but you want a longitudinal straight beam not an angle beam. Angle beam will not produce a significant reflection from a lamination. That is why ASME Code requires base metal be scanned with straight beam transducer to detect laminations prior to performing angle beam inspection of weld.

Your T-mic is actually a longitudinal straight beam transducer and instrument except instead of a display of the returned pulse as in a UT scope, there is a trigger level and timer which returns a decimal number directly proportional to the time from the initial pulse to the return signal, hence proportional to the thickness. When you calibrate the instrument you are setting the 'time' number to read as thickness. When you have a lamination in the plate the ultrasonic signal reflects of the lamination and returns to the instrument in about half the time as a signal which makes it to the ID resulting in a thickness reading of about 1/2 the pipe thickness.

 

[rustbuster]

I would suggest you have a qualified NDE Technician scan the areas with a flaw detector (CRT)and O Degree probe. You would then see the reflections and be able to interpret and size the defects.

Digital thickness meters should be used as "indicative" information, not for examining flaws.

good luck!