Environmental Engineering Reference
In-Depth Information
inevitable, the corroding part should be designed in such a way that it can
be easily replaced. The relative surface areas of anodic and cathodic sur-
faces should not be underestimated. Fastener material should be more noble.
When paint is applied, it is important to paint either the whole assembly
or the noble member of the couple. Application of paint only on the active
metal will aggravate corrosion at the pores leading to rapid pitting. In a
flowing system, nobler metal should be avoided as upstream component,
since ions carried downstream deposit on the less noble metal and induces
galvanic corrosion.
3.
Avoid crevices
. Crevice sites may arise due to the contact of two metallic
components (Fig. 4.16a), incorrect trimming of gaskets (Fig. 4.16b), im-
proper provision of base for a vessel (Fig. 4.16c), riveting (Fig. 4.16d), and
many other situations that should be avoided. Welding rather than riveting
is prescribed to do away with crevices. Use of proper filler material or
sealing is recommended at the crevice sites.
Figure 4.17
Improper and proper drainage in tanks and pipes.
