Red Seal Boilermaker Practice Exam

What does back purging involve in welding?

1. Applying heat to the weld to strengthen it

2. Using an inert gas to shield the backside of the weld from contamination

3. Purging the entire system to remove impurities

4. Testing the weld for leaks after completion

The correct answer is: Using an inert gas to shield the backside of the weld from contamination

Back purging in welding is a technique specifically used to prevent contamination on the backside of a weld joint. This process involves the use of an inert gas, such as argon or helium, which is introduced to the area behind the weld. This shielding gas displaces oxygen and other potentially harmful substances, thereby minimizing oxidation and contamination of the weld area. When welding materials like stainless steel or titanium, where maintaining a clean weld integrity is critical, back purging helps ensure that the welded joint achieves the desired mechanical properties and aesthetic appearance. The inert gas not only protects the surface but also provides a superior quality weld by maintaining a protective atmosphere that supports the welding process. Other options may refer to related processes in welding but do not accurately describe back purging. For instance, applying heat to the weld could be related to pre-heating or post-weld heat treatment but does not involve the protective aspect of gas shielding. Purging the entire system for impurities implies a broader cleaning process, while testing for leaks is more associated with quality assurance after welding rather than a protective measure during the process.