As per API 650, there is one 6 mm (1/4") telltale hole in reinforcing plate, on horizontal centerline to allow breathing of air pockets may be located between reinforcing pad and tank wall due to expansion and contraction of these air pockets especially during welding. And the horizontal location at centerline is preferred because it is located at the middle area of whole reinforcing pad between upper and lower halfs of pad to facilitate good breathing during hot and cold conditions.

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Hi Mr. Abdel Halim Galala

Why this reason not applies to Piping RF pad(B31.3 says that A vent

hole shall be provided at the side (not at the crotch) of

any pad or saddle to reveal leakage in the weld between

branch and run and to allow venting during welding

and heat treatment) and Pressure vessel RF pad (ASME Sec VIII Div.1)?

If I'm wrong correct me pls.

Regards.