Pipefitter Pipe Fabrication and Joining 2

Question 1

What is the minimum preheat temperature required by AWS D1.1 when welding carbon steel with a carbon equivalent greater than 0.40?

Accepted Answer

150°F (65°C)

Answer

AWS D1.1 and ASME B31.3 require a preheat of at least 150°F when the carbon equivalent exceeds 0.40 to prevent hydrogen-induced cracking.

Question 2

When making a socket weld joint, what is the standard gap that should be left between the pipe end and the socket bottom?

Accepted Answer

1/16 inch (1.6 mm)

Answer

ASME B31.3 requires a 1/16" gap between the pipe end and the socket shoulder before welding to allow for thermal expansion.

Question 3

What type of pipe joint is made by heating the end of a pipe and forming a conical seating surface that mates with a flared fitting?

Accepted Answer

A flared joint

Answer

A flared joint is made by flaring the pipe end into a cone shape that mates with the angled seat of a flare fitting, creating a metal-to-metal seal.

Question 4

What is meant by 'back-purging' during stainless steel pipe welding?

Accepted Answer

Flowing inert gas inside the pipe to protect the weld root from oxidation

Answer

Back-purging means flowing argon or nitrogen through the inside of the pipe to displace oxygen and protect the weld root from oxidation (sugaring).

Question 5

In threaded pipe joints per ASME B1.20.1, what is the standard taper of NPT (National Pipe Taper) threads?

Accepted Answer

1/16 inch per inch (1 in 16)

Answer

NPT threads have a taper of 1/16 inch per inch (3/4 inch per foot) as specified in ASME B1.20.1.

Certified Pipefitter Practice Test