K. V. Kasiviswanathan

Meeting the challenges related to material issues in chemical industries

Reliable performance and profitability are two important requirements for any chemical industry. In order to achieve high level of reliability and excellent performance, several issues related to design, materials selection, fabrication, quality assurance, transport, storage, inputs from condition monitoring, failure analysis etc. have to be adequately addressed and implemented. Technology related to nondestructive testing and monitoring of the plant is also essential for precise identification of defect sites and to take appropriate remedial decision regarding repair, replacement or modification of process conditions. The interdisciplinary holistic approach enhances the life of critical engineering components in chemical plants. Further, understanding the failure modes of the components through the analysis of failed components throws light on the choice of appropriate preventive measures to be taken well in advance, to have a control over the overall health of the plant. The failure analysis also leads to better design modification and condition monitoring methodologies, for the next generation components and plants. At the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, a unique combination of the expertise in design, materials selection, fabrication, NDT development, condition monitoring, life prediction and failure analysis exists to obtain desired results for achieving high levels of reliability and performance assessment of critical engineering components in chemical industries. Case studies related to design, materials selection and fabrication aspects of critical components in nuclear fuel reprocessing plants, NDT development and condition monitoring of various components of nuclear power plants, and important failure investigations on critical engineering components in chemical and allied industries are discussed in this paper. Future directions are identified and planned approaches are briefly described

Acoustic emission during tensile deformation of annealed and cold-worked AISI type 304 austenitic stainless steel

The influence of prior cold work on the acoustic emission (AE) generated during subsequent plastic deformation of AlSl type 304 stainless steel has been studied. AE parameters such as root mean square voltage, ringdown counts, etc., have been used to analyse the data. AE generated during tensile deformation is affected by prior cold work. The increase in acoustic activity at low strain levels in a less cold-worked (10%) specimen compared to a solutionannealed specimen was attributed to the easy formation of α′-martensite assisted by prior cold work. The decreased acoustic activity for higher cold-worked (20%, 40% and 50%) specimens at low strain levels was attributed to reduced glide distance for moving dislocations and reduced amount of α′-martensite formation. The AE activity was found to be maximum during higher strain values in the solution-annealed specimen compared to the cold-worked specimens. This was attributed to relatively larger amount of α′-martensite formation in the solution-annealed specimen. Eddy current testing, X-ray diffraction, remanent magnetization measurement and magnetic etching techniques have been used to corroborate the AE results. Among these, remanent magnetization results were found to have good correlation with the AE results.

Study of ageing-induced α′-martensite formation in cold-worked AISI type 304 stainless steel using an acoustic emission technique

Abstractα′-martensite formation during cooling of cold-worked and aged AISI type 304 stainless steel has been studied by an acoustic emission technique. The ageing was carried out at 673 K for 1 h. A substantial amount of acoustic emission generated during cooling of cold-worked and aged AISI 304 stainless steel specimens compared to negligible acoustic emission observed during cooling (after ageing) of annealed AISI 304, annealed AISI 316 and cold-worked AISI 316 stainless steel specimens, was attributed to the α′-martensite formation from cold-worked 304 stainless steel specimens. The extent of martensite formation was relatively higher for 10% and 50% cold-worked specimens and lower for 20%–40% cold-worked specimens. The temperature range of martensite formation, as detected by the acoustic emission technique lies between 603 and 466 K. The formation of α′-martensite has been established to occur by a shear process.

Small Specimen Test Techniques for Estimating the Tensile Property Degradation of Mod 9Cr-1Mo Steel on Thermal Aging

The degradation in mechanical properties of modified (mod) 9Cr-1Mo steel on thermal aging at 923 K has been studied using the small specimen test techniques—shear-punch and ball-indentation tests. Small volumes of material required for these test techniques make them unique tools for the assessment of service related degradation and failure analysis of structural components. A variety of heat treated microstructural conditions of mod 9Cr-1Mo steel is generated on which both conventional tensile test and shear-punch/ball-indentation tests are carried out. The relationship between conventional tensile properties and small specimen test results is established from these standardization experiments. Small specimens of Mod 9Cr-1Mo steel in the thermally aged conditions are tested using both shear punch and ball-indentation techniques and the tensile property changes are determined. Both these tests identically reflect and quantify the changes in the tensile properties with aging time which correlates well with the microstructural changes observed using optical and electron microscopic studies.

Estimation of fission gas release in FBTR fuel pins

Fission gas extraction and analysis has been carried out on fuel pins of fast breeder test reactor subassemblies at different burn-ups as a part of post-irradiation examinations to characterise the performance of the unique mixed carbide fuel and estimate the residual life. This paper describes in detail the fission gas extraction and analysis carried out on fuel pins after various stages of burn-ups of 25, 50 and 100 GWd/t. The analysis of fission gas was carried out by gas chromatography. Analysis indicated that the maximum percentage of gas release is 14% after a burn-up of 100 GWd/t, and the corresponding plenum pressure is 1.2 MPa.

Miniature Shear Punch Test with On-Line Acoustic Emission Monitoring for Assessment of Mechanical Properties

This paper describes the use of acoustic emission monitoring during the shear punch tests to reduce the error involved in the estimation of mechanical property data, especially in the yield strength and strain hardening exponent . Tests have been carried out on a range of materials including AISI type 304 stainless steel containing various amounts of cold work. These data from the shear punch test are compared with tensile property measurements on identical materials. The on-line monitoring capability of acoustic emission technique has been successfully utilized for accurate evaluation of mechanical property data from the shear punch tests.

Failure analysis of an ammonia refrigerant condenser tube

A detailed failure analysis was conducted on an ammonia refrigerant condenser tube component that failed catastrophically during its initial hours of operation. Evidence collected clearly demonstrated that the weld between a pipe and a dished end contained a sharp unfused region at its root (lack of penetration). Component failure had started from this weld defect. The hydrogen absorbed during welding facilitated crack initiation from this weld defect during storage of the component after welding. Poor weld toughness at the low operating temperature facilitated crack growth during startup, culminating in catastrophic failure as soon as the crack exceeded critical length.

Failure analysis of carbonate reboiler heat exchangers

Unacceptably high leakage rates from a large number of type 304 stainless steel tubes forced the scrapping of two carbonate reboiler heat exchangers from the carbon dioxide removal system of a fertilizer plant. Extensive failure investigation carried out on the failed heat exchangers established that the main factor responsible for premature failure of the heat heat exchangers was partial expansion of the stainless steel tubes into the carbon steel tube sheet as against the design specification for the expansion of almost the full length of the tubes inside the tube sheet. Partial expansion of the tubes into the tube sheet left undesirable tube-to-tube sheet gaps, which subsequently acted as crevices and led to localized corrosion of the tube sheet as well as the tubes.

Remote metallographic examination of mixed carbide fuel of fast breeder test reactor in radiometallurgy laboratory

Fast breeder test reactor (FBTR) uses unique, indigenously developed mixed carbide of plutonium and uranium (70% PuC + 30% UC) as fuel. The performance of the fuel was studied at different burn-ups by carrying out post-irradiation examinations (PIE) to facilitate prediction and extension of life for the indigenously developed fuel. As a part of PIE, remote metallography was carried out to study the swelling behaviour of the fuel, estimate the fuel-clad gap and examine the fuel and clad microstructures. Results of the metallographic examinations were used to increase the limit of FBTR fuel burn up and linear heat ratings. This paper describes in detail the remote metallographic techniques adopted during PIE of fuel after a burn-up of 25 GWd/t and 50 GWd/t.

Miniaturized Testing of Engineering Materials

This book is a comprehensive overview of methods of characterizing the mechanical properties of engineering materials using specimen sizes in the micro-scale regime (0.3-5.0 mm). A range of issues associated with miniature specimen testing like correlation methodologies for data transferability between different specimen sizes, use of numerical simulation/analysis for data inversion, application to actual structures using scooped out samples or by in-situ testing, and more importantly developing a common code of practice are discussed and presented in a concise manner.