Sunday, August 23, 2009

RLA/Remaining Life Assessment by TCR in India and Middle-East (KSA, Kuwait, Qatar and UAE)

TCR undertakes comprehensive RLA activities all over the world.

Remaining life assessment concept is based on the philosophy of assessment of present materials integrity vis-à-vis operational demands. The design of material is done on the basis of mechanical properties of the virgin material. Due to continuous use under high pressure and temperature materials properties degrades and it effective life is being consumed. The other degradation process is creep of the material which occurs under high temperature and high pressure normally above 300 Deg C temperature. In general the power plants are designed for 30 years of the creep life.

Thermal and creep degradation of material can be identified with the help of microstructure examination as they are visible under microstructure examination and also can be categorized under different stages hence useful to estimate Remaining life. That's why replica metallography is gaining lot of attention in the Remaining life assessments. The other degradation mechanisms are fatigue and delayed cracking of the weld due to fabrication related defects which they open up after several years of service. They can be triggered by any manufacture flaw, fabrication flaw or during abnormal operations. That is the reason thorough NDT assessments are done to find out presence of any defect which can be found out and repair.

There are two kinds of damages which are observed during operation of high temperate and pressure components. Bulk damage- irreversible damage and other is localized damage which can be repaired. Creep is an irreversible and onset of creep if it is in final stage the component needs to be retired from the plant otherwise it can lead to catastrophic failure. However in case of localized damages like cracking in the weld or flange or bend, which can be replaced or repaired depending upon the nature of the problem. In either case the plant is benefited.

In RLA one can defined the next interval period and maximum life before the next inspection can be predicted is for 5 years for power plants. By adopting this approach every five years or at predefined intervals one get assure about the conditions of the plant and its components. In case of any localized problem is observed it can be rectified and overall integrity of the system can be improved. RLA studies give great benefit to operating plants as they can plan their inventory and components spares which are not fit to withstand up to next shutdown can be replaced as they get uninterrupted service. By adopting this philosophy advanced countries have extracted the life of a power plant or process plant to double or 1.5 times the original design life by running it on calculated risk and assessments.

Even after RLA if any upset in process parameters occurs, failure do occur but in that case reasons of failures are known.

What are the criteria's for RLA, when plant undertake RLA studies?

•INCREASING COST OF NEW EQUIPMENT AND DIMINISHING RESOURCES

•EXTENDED LEAD TIME IN PLANT CONSTRUCTION

•STRINGENT ENVIRONMENTAL, SAFETY AND OTHER REGULATIONS

•INCREASING AWARENESS OF THE TECHNOLOGICAL FEASIBILITY OF EXTENDING COMPONENT LIFE

To avail of RLA from TCR please contact rohit@tcreng.com

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