Failure Analysis of A 304 SS Girdling Loop of the Boiler in a 500 MW Thermal Power Plant

There were many cases of girdling loop failures in the reheater section of the 500 MW boilers of athermal power station after being in service relatively for a short period of a few months. Within seven months of synchron-ization, the bottom 'U'portion of the front reheater girdling loop of the boiler of 500 MW thermal power plant had developed a leak. The plant was restarted alter replacing the failed protion of the type 304 stain-less steel 'U' tube. Failure occurred again within seven months of operation. Similar failures followed in the other units of the station

Influence of secondary phases on the localized corrosion of thermally aged AISI 316L stainless steel weld metal

The pitting resistance of AISI 316L stainless steel (SS) weld metal in as-deposited and aged conditions was evaluated by determining the critical pitting potential in an acid chloride solution. The results indicated that after aging at 773, 873, or 973 K, the pitting corrosion resistance of the weld metal had deteriorated. The decrease in the critical pitting potential upon aging has been discussed in terms of precipitation of the various secondary phases

Evaluation of susceptibility to stress corrosion cracking (SCC) in sodium chloride solution of weldments of cold rolled type 316 stainless steel

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Evaluation of the stress corrosion resistance of cold rolled aisi type 316 stainless steel using constant load and slow strain rate tests

The effect of cold rolling (5 to 15% reduction in thickness) of an AISI Type 316 stainless steel on stress corrosion cracking (SCC) has been studied in boiling magnesium chloride of 45% concentration (boiling point = 428 K) using both constant load and slow strain rate methods. The constant load test results indicated increasing SCC susceptibility with increasing degree of prior deformation, whereas the ranking by the slow strain rate technique was in the reverse order. The reasons for this discrepancy have been discussed. A modified procedure of slow strain rate testing, involving the interruption of the test after a chosen duration of time and measuring average crack growth is suggested as an alternative

Secondary ion mass spectroscopy and surface profilometric characterisation of oxide scales developed over weld metal, heat affected zone, and base metal regions of 9Cr-1Mo steel weldments

Microstructurally different regions (namely the weld metal, heat affected zone (HAZ), and base metal) were characterised in weldments of 9Cr-1Mo steel, and composite specimens comprising the three regions were oxidised in air at 923 K. As measured by surface profilometry, the weld metal region was found to form a thicker oxide scale than the other regions of the weldment. The difference in thickness between the scales over the weld and adjoining H AZ regions was found to be ~5 μm after 4 h but had increased to ~100, μm in 100 h. Difference in thickness between the scales was also confirmed by a few examinations using scanning electron microscopy (SEM); this method also described the difference in morphology of the scales developed over the three regions. Secondary ion mass spectroscopy (SIMS) depth profiles of iron and chromium in scales developed over the different regions of the weldments have suggested a considerably higher chromium content of the inner scales on the H AZ and base metal than that of the scale over the weld metal; SIMS profiles have also corroborated formation of a thicker scale over the weld metal, as assessed earlier by surface profilometry and SEM

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