J. Swaminathan

Analysis of failed reformer tubes

Reformer tubes from a fertilizer plant made of modified HK 40 steel which failed after 4 years service were investigated for failure mechanism and life evaluation. The investigation included hot tensile tests, hardness measurement, dimensional measurement, microscopy and a few accelerated creep tests. Analysis revealed that longitudinal cracks found in the tubes were caused by overheating because of inadequate feed flow caused by the choking of damaged catalyst. To avoid such choking, precautions should be taken while charging the catalyst that no broken piece of catalyst or any external material goes along. Nitrogen which is used for cooling down the tubes and which was retained inside during idle periods should be dry enough. Overheating during service is primarily responsible for significant degradation in mechanical properties and microstructures in the bottom portion of the reformer tubes.

Effects of Cold Deformation Prior to Sensitization on Intergranular Stress Corrosion Cracking of Stainless Steel

Abstract The effects of deformation, prior to sensitization, on intergranular stress corrosion cracking (IGSCC) were studied on the AISI 304 (UNS S30400) stainless steel (SS). The degree of sensiti...

Microstructural and textural evolution during large strain hot rolling (LSR) of Mg–Al (AZ31) alloy

Abstract Grain refinement has been achieved through large strain rolling (LSR) in Mg AZ31 alloy. The evolution of microstructure and texture has been found to be dependent on the amount of reduction. After the critical amount of reduction, grain refinement proceeds through continuous dynamic recrystallisation (CDRX).

Remaining life assessment of service exposed reactor and distillation column materials of a petrochemical plant

Mechanical property evaluation is a powerful tool for estimating the residual life of in-service components and health monitoring. In the present investigation such an assessment was carried out to estimate the remaining life of in-service plain carbon steels that had been in use for 45 years in a feed processing unit (FPU) of a petrochemical plant. Health assessment of both base and weld joints of the material has been carried out through accelerated stress rupture tests and other mechanical property evaluation. At the operating conditions, it is noted that the materials still have about 10 years of residual life. However, surprisingly weld joints of the column of this unit exhibited poor notch toughness (5–10 J). It could not be proved beyond doubt, if the weld developed poor notch toughness during fabrication or degraded during service. Annealing of weld joints at 530 °C for 1.5 h improved the notch toughness significantly, hence is recommended accordingly.

Residual Life Estimation of Service Exposed Reheater Tubes in a Boiler of a Thermal Power Plant

The consequence of service failure can be tragic and expensive. There are many cases of engineering disasters resulting in loss of life and property. For boiler components the utmost attention is a must to ensure that such incidents do not take place. Life assessment exercise performed at regular intervals is a means to ensure the absence of such tragic service failure. This paper presents the high temperature tensile and the stress rupture properties of 149084 hours service-exposed reheater tubes made of 2.25Cr-l Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours 100,000 hours rupture strength as obtained from experimental data in the temperature range of 520°C to 580°C exhibit a decreasing trend with increasing temperature. The effect of oxide scale deposition on the inner surface of the reheater tubes on the remaining life of the tubes has been discussed. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level of 40 MPa /540 °C, provided no localised damage in the form of cracks or dents has developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 540 °C.