Lapped patch repair plates may be used to repair small leaks or minimize the potential of leaks from isolated pitting. The requirements for thickness and design are the same as for reinforcement of shell thickness. This type of repair may not be used to repair small leaks if what condition(s) exists?

The leak is located anywhere in the first shell course within 12 inches of a vertical joint

The leak of pit is in an area of the shell where there is a product to atmosphere interface

There is a possibility of severe environmental impact should the repair fail

If exposure of the fillet weld to the product would produce crevice corrosion or if a corrosion cell is likely to occur between the shell plate and the repair plate