Soot blower heads must be replaced when the head thickness has reached what percent less than the original thickness specified on the applicable drawing when measured by ultrasonic testing?

The correct answer is based on the importance of maintaining the structural integrity and operational efficiency of soot blower heads in a steam plant. Soot blower heads are subject to wear and corrosion due to the high temperatures and abrasive nature of the soot they are designed to remove from the heat transfer surfaces.

Ultrasonic testing is a nondestructive testing method that evaluates the thickness of materials. The standard threshold for replacing soot blower heads is established at 50% of the original thickness. Reaching this level of material loss signifies that the head may no longer provide the necessary strength or functionality, potentially leading to failure during operation. Regular monitoring and replacement at this threshold help ensure the reliable performance of the soot blowers and maintain the efficiency of the overall system.

While other options reference various percentage thresholds, only the 50% figure aligns with standard practices in the industry concerning safety and equipment longevity.