Which of the following is true about hammer testing?

Hammer testing, also known as ping or tap testing, is a non-destructive testing method that involves striking the surface of a material and listening to the sound produced. The key aspect of this method is that variations in sound can indicate differences in material properties, such as thickness. When a hammer is struck against a surface, a clear sound typically indicates good thickness, while a dull sound may suggest a thin or degraded area. This reliance on sound and tactile feedback allows inspectors to effectively identify thin spots in pressure vessels.

The method does not require advanced technology; it can be performed with simple tools and by trained personnel. It is also applicable to vessels of various sizes, not limited to large ones, and can uncover thickness variations, making this option the most accurate regarding the capabilities of hammer testing.