Dear all,

In API 650, subject single welded lap joints of the tank roof plate is shown as " Top edge of the bottom plate shall be at the underneath of the bottom edge of the top plate" which shall give raise to no accumulation of water o0n roof during rainy seasons.

However with the above arrangement thee is a chance of entrapment of process vapours between the lap area at the underneath of the tank roof i.e. indie the tank and in turn may corrode the roof plate at these areas.

In view of the above , to address both the issues double side lap welds shall be given, However considered the water storage in the tank and with single welded lap joint, any body can confirm which type of lap design is preferable

Thanks in advance