IEC IEEE 62582-2-2011 pdf download Nuclear power plants – Instrumentation and control important to safety – Electrical equipment condition monitoring methods – Part 2: Indenter modulus
General description
A typical indenter uses an instrumented probe, which is driven at a fixed velocity into themateral and includes a load cell or similar force-measuring device, connected to the probewhich measures the force necessary to maintain the constant velocity. The probe’sdisplacement is measured by an appropriate transducer. The travel and force are purposelylimited to protect the material from permanent damage, The indenter modulus is calculated bydividing the change in force by the corresponding displacement during inward travel.
5 Applicability,reproducibility, and complexity
5.1General
When organic and polymeric materials age, they often harden which will result in an increaseof indenter modulus. Some materials, such as some formulations of Butyl Rubber, softerduring thermal and/or radiation ageing. The purpose of monitoring changes in indentelmodulus is to estimate degradation rates and levels induced by ageing.
5.2Applicability
The indenter method is commonly used to carry out measurements on cables (iacketsinsulation) and o-rings. lts use requires special fixtures depending on the geometry of thesamples.
This method should only be applied to materials whose hardness changes monotonically withageing.
The indenter method may be carried out on equipment with high integrity in a non-invasivemanner. However, the process of performing indenter measurements on equipment in fieldshould include controls to ensure that damage from the probe or from handling in order toaccess suitable measurement points – has not been imparted to the equipment. The processshould include correction of any equipment that has been damaged orsuspected of incurringdamage
Measurements in the field require access to the exterior wall of the equipment. For fieldmeasurements on cables, this often limits the measurements to jacket materials. lt may bepossible to assess the condition of cable insulation from indenter measurements on its jacketif there is a known relationship between the ageing degradation of the jacket material and thedegradation of the insulation. This relationship shall be justified to be valid and sufficientlysensitive to provide the valid monitoring through life.
5.3Reproducibility
Indenter modulus valuescan be influenced by variability in specimen dimensions andconstruction, temperature and moisture content of the specimen, stabilisation of thespecimen, and contamination of the specimen. if measurements are made under excessivevibration, this can influence the measured value. The influence by variability in the specimendimensions and construction is typically the case for measurements on cables, where themeasurement point may be situated above a cavity beneath the jacket surface. The cross-section of typical cable core insulation may differ substantially from that of an ideal tube andcan result in variability in the measured values of indenter modulus depending on where themeasurement is made. These variations tend to be localised. Measurements shall be taken atseveral points on the equipment to compensate for these local variations (see 6.6)
An illustration of variations due to variability in specimen dimensions and construction is givenin Annex A.