what is the correct procedure for UT examination of 1.5 inch pipe weld 3

[tigwired]

Am having several welds inspected utilizing UT, am wondering if grinding the caps off is the way to go?
Should the procedure be straight through inspection or shear wave inspected?
Diameters are 20 inch with a 1.5 inch wall thickness.

 

[unclesyd]

Planishing a 20" dia weld is quite a chore and is very had to get a smooth even surface on this dia.

With your same machine why can't you use an angle beam transducer?

Any UT Technician should easily handle the task if enough room is available for the standoff.

 

[JR97]

tigwired,

Short answer - angle beam will yield much more meaningful results than straight beam. Straight beam will only find volumetric defects such as slag or lamination type defects in adjacent base material. Angle beam will find the slag as well as much improved detectability of lack of fusion and other throughwall type defects.

If the weld cap is not ground off, there will be little impact to the perpendicular scan, as unclesyd said, as long as the technician can start his scan far enough from the weld. The more significant impact is for the parallel scan. This scan will detect defects lying primarily across the weld. With a weld cap, all the technician can do is pass the transducer along the edge of the cap and skew the transducer to try to see under the cap.

My bottom line is to look at your materials and process and determine if there is a concern with across the weld defects (e.g. hydrogen cracking). If there is a concern, take the cap off to get full coverage. If no particular concern with across the weld defects, leave it on.

JR97

 

[ndeguy]

tigwired

1st as both unclesyd and JR97 point out all welds requiring full UT should be examined by a comprehensive inspection plan designed with critical areas in mind (sidewall, root, toes of weld cap and HAZ) as well as a general examination of the body of the weld. This demands the use of various angle beam shear wave probes . International Codes demand this virtually without exception - successful UT examination requires perpendicualr incidence (+/- 10 degrees) on critical target areas such as sidewall fusion zone. Thus for a 30 degree bevel (60 degree included angle) a 60 degree probe is essential for adequate reflection from sidewall defects.

20" OD, 38mm wall piepwelds are ideal for UT of pipe to pipe welds. However pipe-to-fitting welds may have some access problems from the fitting side precluding full inspection from both sides of the weld. This limits the inspection especially of the top portion of the fitting-side fusion face for lack-of-sidewall fusion defects. Its possible to put sound into that region but its orientation will be oblique and so insufficient sound will return to the probe for detectionpurpises.

There are ways round this depending on the weld geometry. Sometimes creep wave probes of sufficient range (creep waves attentuate rapidly through metal) are used from the pipe side. In other cases full cap removal is not necessarily required, grinding the cap flat (not flush) will allow internal reflection from the cap without scattering or changing the reflected angle of the beam.

However more often than not such conditions are reported as a test restriction, this may be sufficent for non-criticcal welds but for high pressure, cyclically-loaded or lethal service welds your next step would be to fabricate a represntative mock-up containing purposely introduced known defects and then running trials to determine defect detectability in these regions.

Advanced UT such as TOFD and Phased Array have the same problem as manual UT but can be better controlled and offer permanent digital records.

Consult a professional UT Level III with demonstrated experience in these matters.