Weld Size , and Hot Tapping (Chap 6-7 / A4.5)

Question 1

What are the requirement of hot tap?(4)

Answer 1

(1) . atleast 3 feet below liquid level (to act as an heat sink)*
(2) . Reinforcement plate shall be pneumatically tested *
(3) . Welding shall be done with low hydrogen electrodes*
(4) hot taps to be made in locations where hoop stress from hydrostatic heat are< 7000 PSi

Question 2

Before u make a hot tap what needs to be done?(2)

Answer 2

Inspect the area and take UT thickness, at least 4 locations around the nozzle location

Question 3

When is hot tap not allowed?(5)

Answer 3

1. On material that requires thermal stress
2. severely pitted area or laminated areas
3. not on roof and vapor space
4. Reinforcing plates for hot-tapped nozzles shall not cross any shell plate seams or extend to the shell-tobottom joint weld
5. Hot taps are not permitted on tanks where the heat of welding may cause environmental cracking

Question 4

What is the limitation of NPS for unknown toughness for hot tap?

Answer 4

limited to 4” (no limits for known toughness)

Question 5

How to calculate the min spacing in any direction (toe-to-toe of welds) between the hot tap and adjacent nozzles ?

Answer 5

square root of RT