Fault Diagnosis: Diagnostic Maintenance

This maintenance method is viewed as a part of CBM by most of the plant managers probably due to the reason that the techniques employed are almost similar. The choice of the monitoring techniques to be applied in particular plant is difficult, affected by such factors as skills available, effect of the environment, reliability of the machines and the monitoring methods, etc. This decision tends to be made on an ad-hoc basis of personal experience or advise to be developed. But the Diagnostic Maintenance uses the scientific methods and analysis of failures to detect and rectify the faults.

Most of us have experienced the situation of going to a pathological laboratory for a blood check up or urine examination or any related tests referred by our doctor when we visit him with some ailment. Although the doctor knows or suspects the disease he does not diagnose and treat immediately. Do you know why? Because he wants to confirm it through scientific test, to know the severity of the problem and to check any scope of development of other linked problems. A Plant Engineer is none less than the doctor for his machine and hence it necessitates him to completely diagnose the fault before his treatment starts. Various tests are available for the Plant Engineer, which can be categorized into two main groups as:

• Destructive Tests (DT), and
• Non Destructive Tests (NDT).

There are numerous Destructive Tests to know if the material of the machine part is subjected to any deterioration due to stress, impact, creep, fatigue and thermal effects. These tests will be resourceful to the plant engineer in ensuring whether to continue or to replace the machine parts. In fact these tests are performed occasionally by the plant engineer to confirm when he gets any doubt on the machine part but not regularly. A plant engineer shows much interest and gives utmost importance to the Non Destructive Tests rather than Destructive Tests as the latter involve the destroying of the part while the former can identify, detect and indicate the severity of the problem without actually destroying the part and thus facilitates the engineer to use the same part if he feels that the replacement is not immediately necessary. (However, these tests are dealt in the course metallurgy/material science and strength of materials. The readers are advised to go through these subjects for more details of Destructive Tests. However, a few most important tests are briefed out here for ready reference).