Minor Damage Testing
Some Non Destructive Testing is actually minimally invasive and produces some minor damage on the material or assembly.
The most common form of Minor Damage Testing referenced as NDT involves pulling on a surface or partially embedded object and measuring the force. This includes Coating Adhesion Testers, which pull off a dolly epoxied to a surface coating. Similarly, the Pull-Out Strength or withdrawal resistance of roof fasteners can be tested. Adhesion of concrete patches can be tested using the Pipe Test Method, and metal inserts can be embedded in new concrete and removed using a Pullout Test as an estimate of compressive strength.
A variation on pull-out testing is Flat Jack Testing of brick and mortar assemblies. A horizontal mortar joint is sawed out and a flat jack inserted and inflated, while the distance between the upper and lower bricks is monitored with an extensometer. This will provide information on whether load has shifted to a non-load bearing wall.
A simple form of Minor Damage Testing is to drill a hole and insert a Borescope to visually inspect the spaces in a cavity wall. Sometimes the behavior of the drill itself is closely monitored to measure the Drill Resistance of the material.
Testing not included under Non Destructive Testing
Tests where dust, prisms, or cores are extracted and transported to a lab for testing, or where chemicals or tests strips are applied in the field and observed for reactions, are more properly characterized as Materials Testing rather than Non Destructive Testing, whether or not they are performed in the field ("in-situ") and whether or not the damage or residue is permanent, minor, or temporary.
Similarly, monitoring a material or assembly over time is more properly characterized as Structural Health Monitoring (SHM). This also goes for Vibration Monitoring and Land Surveying.