Critical Zone

Question 1

Maximum plate thickness for welded-on patch plates within the critical zone is ,,,,,,. and must meet the toughness requirements

Answer 1

1/4-in (6.35 mm)

Question 2

Perimeter welds on welded-on patch plates within the critical zone shall be,,,,,,minimum

Answer 2

two-pass,

Question 3

Installation of a welded-on patch plate by butt-welding to an adjacent existing patch is ,,,,,,,, in the critical zone

Answer 3

not permitted

Question 4

Welded-on patch plates over existing patches are ,,,,,in the critical zone.

Answer 4

not allowed

Question 5

No welding or weld overlays are permitted within the critical zone except for the welding of: ,,,,,,

Answer 5

• widely scattered pits
• pinholes, cracks in the bottom plates,
• the shell-to-bottom weld,
• welded-on patch plates, or
• where the bottom plate welded to the shell is being replaced.

Question 6

Welded-on patch plates are not permitted in the critical zone on a tank bottom with an operating
temperature exceeding for ,,,,,carbon steel or ,,, for stainless steel.

Answer 6

200 °F

100 °F

Question 7

If more extensive repairs are required within the critical zone , the bottom plate welded to the shell shall be ,,,,,

Answer 7

cut out and a new plate shall be installed

Question 8

The repair of corroded plates in the critical zone is limited to ,,,,,or,,,,,,,,welding

Answer 8

pit welding or overlay welding

Question 9

The minimum acceptable bottom plate thickness for weld repairs is ,,,,,

Answer 9

0.10 in (2.54 mm)