What is no destructive test ?

This refers to NDT - often used in structural maintenance in Pillars and solid block building/structures.

It is used to find fault line and imperfections using high frequency ultrasound and a sensor

Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage.

Destructive Test is the test performed on materials or system, after which the materials can not be used as designed for. This test is perform the maximum capacity/strength to withstand on applied external source.

For example, the dielectric test of cables to perform until it breaks the dielectric strength. After the test insulation resistance will not be same as it was as per  original design. The sample piece becomes unusable.

destructive testing (DT)  methods where material is broken down in order to determine mechanical properties, such as strength, toughness and hardness. In practice it means, for example, finding out if the quality of a weld is good enough to withstand extreme pressure or to verify the properties of a material.

A test in which the sample is unusable after test.