I realize you posted this in the AWS forum but we weld lots of ASME pressure vessels with GMAW that are 100% RT inspected. there is no reason why GMAW welds should fail an RT inspection.
The question is not whether the welds would fail radiography, but rather if radiograph is capable of detecting serious flaws that can be present in a short circuit GMAW joint. I believe weldtek has the correct approach, and it seems Redhead1963 agrees.
The answer is yes. Provided all the radiographic parameters for density, sensitivity and latitude are met you will be able to pick up any flaws that would normally show in any other welding process.
The orientation of the discontinuity relative to the axis of the beam f ionizing radiation will influence the ability to detect planetary discontinuities.
If the planetary discontinuity is parallel to the beam the probability of detection is high. If the orientation of the planetary discontinuity is perpendicular to the beam the probability is very poor. Radiographic examination is not likely to detect discontinuities such as laminations, delaminations, or incomplete fusion to a backing bar. The discontinuity does not represent a change in thickness or density along the axis of the radiation.
Incomplete fusion between layers of weld beads may fall into the same category as a lamination because it may not be oriented in a favorable direction relative to the radiation.
A crack is often parallel to the axis of the radiation beam and detects cracks that do represent a change in material thickness.
Incomplete fusion, especially when welding with GMAW-S, may occur between the weld bead and the groove face. Depending on the orientation of the radiation, it may or may not detect the discontinuity. This can be very troublesome when “shooting” with an offset. The incomplete fusion parallel to the beam will be detected while the opposite groove face will be more perpendicular to the radiation beam and may be missed entirely. Consider a bevel groove with a groove angle of 45 degrees. If the radiation source is located on the side opposite the bevel and places such that it is 45 degrees to the test surface places the incomplete fusion to the groove face perpendicular to the energy beam. It is highly improbable the incomplete fusion will be detected. Changing the position of the source such that the axis of the radiation beam is parallel to the 45 degree groove face changes everything. The probability of detecting the incomplete fusion between the weld and the groove face is excellent.
The same tricks can be played when using ultrasonic testing with a shear wave, but the favorable orientation is perpendicular to the sound beam.
I see Microsoft did an automatic spell check and changed a few words for me. The word "planetary" was supposed to be "planar."
I don't disagree that welds deposited with GMAW-S can be examined using RT. However, since GMAW-S is known for the tendency to suffer fusion type discontinuities, it is something to keep in mind when performing any volumetric examination.
Thanks to all who responed. And maybe acceptable was not the right word to use in this case. But gtaw hit the nail on the head. That is what I have learnt in the past and in CWI school. All you people are great and thanks again for all the input.
A common misconception is that LOF problems are only encountered with GMAW-S.
All GMAW can be susceptible to LOF problems based on the welders technique.
I was in the unique position years ago in New Zealand where I would witness the welder qualification tests as a third party and then take them back to our lab and radiograph them myself.
I could basically tell who was going to fail before I had even radiographed them based on the welders who tried to "push" the torch rather than pull/drag.
Even with spray transfer, if the molten puddle is getting pushed ahead of the arc then the arc cannot come in to contact with "clean" metal and LOF problems come into play.
Agree totally with Als comments regarding the difficulty of identifying all LOF discontinuities with RT,
Cheers,
DD
Sec IX recognizes that GMAW is prone to fusion type defects in the short circuit mode and that RT has some limitations in revealing them. Therefore the prohibition in QW 304.
