RBM (Risk Based Maintenance) is a promising method of maintenance for aged plants. The Risk is defined as the product of likelihood and consequence of failure. The likelihood of failure is evaluated by prediction of residual life or sensitivity of failure and degradation. Technical module is a tool to evaluate the likelihood of failure. In this paper development of technical module for erosion-corrosion which is one of the most likely mechanism of failure in aged plants is introduced.
The contribution of the fluid mechanics to the piping wall thinning phenomena was investigated. It was shown that the fluid force to the wall was quite different between flow accelerated corrosion (FAC) and erosion. The turbulent mass transfer, which is one of the primary factors of FAC, was analogous to the turbulent heat transfer. The model that the molecular transport in the viscous sublayer nearby soon of wall was predominant was practicable. In addition, the mass transport was predicted using commercial codes of computational fluid dynamics. Some prediction results of the mass transfer in orifice and the elbow using above techniques were explained.
Incubation times of stress corrosion cracking (SCC) for mill annealed and cold rolled type 316L stainless steel (SS) and type 316 SS were examined by the creviced bent beam method in oxygenated high temperature water at 561 K. SCC was observed in type 316L SS after exposure of 1000 h to the test environment, although type 316 SS showed SCC susceptibility after exposure of 500 h. The fracture surface of both type 316L SS and type 316 SS consisted mainly of intergranular SCC with a small fraction of transgranular SCC similar to those observed in the actual components. The maximum SCC crack length [a] on the specimen surface increased in proportion to the logarithm of the exposure time [t] for each SS as ; a=700×ln(t)–4334 : type 316L SS, a=1078×ln(t)–6347 : type 316 SS. The incubation times of 490 h and 360 h were obtained for type 316L SS and type 316 SS, respectively, from the relationship between the crack length and the test time. The SCC incubation times were larger than that of sensitized type 304 SS by >3 times showing higher resistance to SCC of mill annealed, low carbon stainless steels.
The carbonation of Mg(OH)2 by carbon dioxide in air was examined. Compound, chemical composition, and surface property of the calcareous deposit formed in tidal zone were investigated. As a result of the carbonation of Mg(OH)2, dypingite was formed. Inside of the calcareous deposits composed of rust and Mg(OH)2 and dypingite. Outside of the calcareous deposits composed of aragonite and dypingite. Thus, it is considered dypingite in the calcareous deposit were formed from Mg(OH)2.