Which of the following is a leak testing method?

The bubble or soap test is a widely used method for leak testing because it allows for the easy detection of gas or air leaks in a system. This technique involves applying a soap solution to joints, seams, or potential leak points on a surface. When a leak is present, the escaping gas will create bubbles in the soap solution, making it visually obvious where the leak is occurring. This method is particularly effective for small leaks and is often used in plumbing, HVAC systems, and gas fittings.

Other methods mentioned, such as thermal testing, gravity testing, and magnetic testing, are utilized in different contexts but do not specifically relate to leak detection in the same manner. Thermal testing is often employed to evaluate thermal performance and can identify issues with heat loss but does not directly assess leaks. Gravity testing usually pertains to the assessment of structural integrity rather than detecting leaks. Magnetic testing is typically used for examining the integrity of materials, particularly metals, by identifying defects and discontinuities, not for identifying leaks. Therefore, the bubble or soap test stands out as a dedicated and effective leak testing method.