Examination and tests of MOVs are performed basically in three - In Manufacture Inspection (IMI), Pre-Service Inspection (PSI) and In-Service Inspection (ISI) - stages. Besides these, on-line conditioning monitoring of MOVs is also developed and applied.

Tarapur Atomic Power Station, the first nuclear power plant in the Indian subcontinent has a wide range of MOVs in its systems. As a part of our maintenance activities and the plant life management programme, we carry out IMI, PSI, ISI and diagnostic analysis of MOVs. In this paper, we briefly explain the various examinations, tests and analysis being carried out on MOVs.

In Manufacture Inspection of MOVs cover all examination specified in the approved quality control plan which include chemical, physical and metallurgical testing of raw materials, finished products NDE of pressure retaining components and hydrostatic testing of assemblies.

Pre-service inspections not only ensures the general condition of the installed valve but also helps to establish a base line data for future operation and maintenance tests. During PSI valve performance data such as motor currents, opening and closing time, seat leakage rate, limit switch (LS) and torque switch (TS) actuation points etc. are collected and archived.

In-service tests are done in accordance with the requirements of ASME/ANSI OMa part-10. The different values collected are compared with the pre-operational data obtained during PSI. This can ensure the healthiness of the system and ascertain the design features.

Of late valve diagnosis using current signature monitoring and analysis has gained wider acceptance and moreover it has become a regulatory requirement. The motor current signature analysis is capable of detecting and diagnosing valve problems such as drifting of LS and TS settings, hard lubricants, mechanical problems in operator, bend shaft etc.

Although the focus here in this paper is on nuclear power plant MOVs, this may find application in fossil fuelled power stations and other process industries.