In a recent modular construction project, severe corrosion of the gasket contact surfaces of flange faces was found to have occurred after the flanges had been tightened.1 Root-cause analysis indicated that there is a greater chance of water ingress in tightened flanges in modular construction than in stick-built construction and that the longer construction period in the former can result in the severe corrosion of flange faces observed. Therefore, in order to mitigate or prevent such corrosion in modular construction, countermeasures should be taken. In this paper, two means of mitigating or preventing flange face corrosion in tightened flanges (i.e., a rust preventive coating and a special spiral wound gasket) were tested, and these tests confirmed their effectiveness.
It has generally been thought that as long as flanges are properly tightened, no particular corrosion of the flange faces would occur during plant construction. However, in a recent plant construction project in which modular construction methods were used, severe corrosion of gasket contact surfaces in tightened flanges was found at the plant construction site.
The plant was partially constructed in module fabrication yards, far from the plant site, and the modules were transported to the plant site by sea. Despite the flanges having been tightened at the module fabrication yards, severe corrosion of the flange faces, including the gasket contact surfaces, was found at the plant site (Figure 1).
Root-cause analysis indicated that there is a greater chance of water ingress in tightened flanges in modular construction than in stick-built construction. Also, the period from flange tightening in the module yard to start-up of the plant is much longer than in stick-built construction. They, combined with the fact that both, the module fabrication yards and the plant site, were in tropical regions, resulted in the severe corrosion observed.
In order to mitigate or prevent corrosion of flange faces in such projects, countermeasures should be taken, and considering the huge number of flanges, those measures should be simple and practical to apply. In this study, two such measures were tested on tightened flanges: one was a rust preventive coating applied by an aerosol spray and the other was a special spiral-wound gasket (SWG).2