magnetic particle test for shell to bottom joint as per API 650

[mechfabricator]

In M.4.2 for the shell to bottom joint we shall do as following:
"MT shall be performed at every 13mm of deposited weld metal while the weld is being made and on the completed weld."
if the bottom plate is 10mm thk. and first course shell is 12 mm the fillet weld size is smaller than 13mm, then is that necessary to perform MT as above?
generally, what is the meaning of

 

[fegenbush]

It is necessary to perform the MT per M.4.2 for a weld of 13mm.

If you are depositing less than 13mm of weld, it is only necessary to MT one complete pass around the internal and external fillet weld. An additional pass would be required were you to exceed the 13mm limit.

 

[Duwe6]

Meaning 1/2-inch 13mm depth of deposited weldmetal. Basically, one full weld pass. Typically, we just MT each weld pass, and make sure if the tank welders are using 'Jet Rod' E7028 5/32" diameter, that they move fast enough to not exceed that 1/2-inch 13mm maximum per weld bead.

On your tank, you would only need to do the cap = Final Weld, if nobody laid down a first pass that exceeded 1/2-inch 13mm.

 

[IFRs]

See 5.1.3.6
Two pass welds are required for shells of any thickness if the shell is group IV or above, for any hand weld for groups III and below if more than 1/4" fillet, etc... The MT would still be once for every 13mm or partial. Fillet welds are measured not by depth but by leg length.

 

[Duwe6]

"Fillet welds are measured not by depth but by leg length"
Depends. API refers back to ASME IX, and leg length [with allowanced for theoretical & actual throat] are used, and AWS D1.x even gives great illustrations of leg vs. throat.

BUT our Continental brothers use EN, ISO, and DIN. Those typically use effective throat.

 

[mechfabricator]

thank you all,
but in our tank the material is group I, is that possible to eliminate the MT, because the weld size is less than 13 mm.(shell is 12, bottom is 10 mm)
Thank you

 

[fegenbush]

No, it is not possible to eliminate MT.