If possible, remove the entire failure region with some adjacent sound material.

If failure sites are numerous, try to select samples of failure sites with different appearances and/or from locations with potential differences in operating conditions.

In many cases, it is useful to remove mating components, as well as the failed parts, e.g. collect the nuts from failed fasteners or gears and bearings with a failed shaft.

For large structures, obtain material sample(s) well away from the failure to allow comparison of materials properties, e.g. sample a ruptured boiler tube at the failure and in a colder region, such as near the tube sheet.