Pipefitter Welding and Joining Techniques 4

Question 1

What is the primary purpose of back purging with argon gas when welding stainless steel pipe?

Accepted Answer

To prevent oxidation on the inside of the pipe

Answer

Back purging with argon displaces oxygen inside the pipe, preventing oxidation (sugaring) on the weld root, which is critical for corrosion resistance in stainless steel.

Question 2

In orbital welding, what does the term 'weld schedule' refer to?

Accepted Answer

A pre-programmed set of welding parameters for a specific pipe and material

Answer

A weld schedule in orbital welding is a stored set of parameters (amperage, travel speed, pulse settings) programmed for a specific pipe diameter, wall thickness, and material.

Question 3

When using an oxyacetylene torch for pipe brazing, the correct flame adjustment for most copper alloy work is:

Accepted Answer

Neutral flame

Answer

A neutral flame (balanced oxygen and acetylene) is correct for brazing copper alloys as it neither adds carbon nor oxidizes the base metal.

Question 4

What is the minimum preheat temperature typically required for P91 chrome-moly alloy steel pipe welding?

Accepted Answer

400°F (204°C)

Answer

P91 (9Cr-1Mo) alloy steel requires a minimum preheat of 400°F (204°C) to prevent hydrogen-induced cracking and ensure proper martensitic transformation.

Question 5

Which welding discontinuity is most likely to result from improper interpass temperature control during multi-pass pipe welding?

Accepted Answer

Hot cracking

Answer

Excessive interpass temperatures increase the heat-affected zone and can cause hot cracking in materials susceptible to liquation cracking between passes.

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Pipefitter Welding and Joining Techniques 4