Millwright Certification Welding and Cutting Processes 2

Question 1

What is the primary purpose of a shielding gas in GMAW (MIG) welding?

Accepted Answer

To protect the molten weld pool from atmospheric contamination (oxygen, nitrogen, hydrogen)

Answer

To heat the base metal faster

Answer

To improve the visibility of the weld

Answer

To cool the weld joint more quickly

Question 2

When making an oxy-fuel cut on carbon steel, what causes the actual cutting action?

Accepted Answer

A high-pressure oxygen stream rapidly oxidizes (burns) the preheated steel, and the force of the oxygen blows the molten oxide away

Answer

The flame melts through the steel

Answer

The acetylene pressure forces the metal apart

Answer

Thermal shock cracks the steel along the cut line

Question 3

What is the main advantage of plasma cutting over oxy-fuel cutting?

Accepted Answer

Plasma cuts faster, works on any electrically conductive metal, and produces a narrower kerf with less heat distortion

Answer

Plasma torches are cheaper to purchase

Answer

Plasma cutting produces no sparks

Answer

Oxy-fuel cuts are always cleaner

Question 4

What does preheat accomplish before welding on thick or high-carbon steel?

Accepted Answer

It slows the cooling rate to prevent hydrogen cracking, reduces residual stress, and allows hydrogen to diffuse out of the weld zone

Answer

It makes the weld look better

Answer

It increases the welding speed

Answer

Preheat is only for aesthetic purposes

Question 5

What is undercut in welding, and what causes it?

Accepted Answer

A groove melted into the base metal at the weld toe that is not filled by weld metal, caused by excessive current, speed, or improper technique

Answer

Extra weld metal deposited at the toe

Answer

A crack in the center of the weld

Answer

Excess spatter around the weld

Question 6

Why must acetylene gas never be used at pressures exceeding 15 PSI (103 kPa)?

Accepted Answer

Acetylene becomes unstable and can spontaneously decompose explosively above 15 PSI gauge pressure

Answer

It becomes less flammable at high pressure

Answer

Higher pressure wastes gas

Answer

The regulator cannot handle higher pressure