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Technical Discussions
Biju Varghese
Biju Varghese
11:36 Jun-15-2009
Tandem testing of LSAW/Spiral Pipes



I would like to have views regarding tandem testing for mid wall defect in longitudinal/Spiral SAW pipes as per Shell specification (DEP 31.40.20.37 annex d) for automated UT testing in pipe mill. As per the specification we have to use only 45 deg shear wave probe for transmitter and receiver probe. The problem we face is that the reflected angle from inner surface changes depending on the thickness to diameter ratio of pipe and hence to use receiver probe with same angle is not possible. Because of the change in the angle of the returning beam that bounces off the inside diameter of the pipe, the received angle (with respect to the outside surface) will not be the same as the transmitted angle. The skip distance will also change depending on t/D ratio.
As per our trials we have found results are very good with 60/70 deg combination for transmitter and receiver probe depending on t/D ratio of pipe. With 45/45 deg combination we are unable get the results. Why code specs only to use only 45 (± 3) deg probe for both transmitter and receiver?

    
 
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Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
13:44 Jun-15-2009
Re: Tandem testing of LSAW/Spiral Pipes
In Reply to Biju Varghese at 11:36 Jun-15-2009 (Opening).

Biju...API5L is a common standard for Line Pipe and other national and international standards are similar. In the Standard there is no restriction on refracted angle to be 45 degrees. It could be that the person responsible for the company "specification" did not make provision for more effective inspections. API5L in 9.7.4.1 indicates that ANY equipment may be used. However, when used in the pulse-echo mode, it will be very difficult for an operator to correctly position the probes for the midwall region with any angle when required to use the notches or even the through hole because the "maximum amplitude" will generally be from the corner at either the ID or OD. To address this and get midwall coverage, the company I used to work for made a specification to use a calibration standard that used flat bottom holes aligned with the weld centreline in addition to the 1.5mm diameter through hole. Your suggestion for a tandem configuration would be a good option for a "practical solution" to the problem. A description of our concerns in 1998 was made in an article on NDT.net http://www.ndt.net/article/v04n11/eginzel/eginzel.htm
If the client is responsible for setting a specification that limits the efficacy of the guidelines set by the Standard then I would suspect they are also responsible for the outcome.

    
 
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