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Corrosion, pitting, cracking take no prisoners

Corrosion, pitting, cracking — those are worrisome words for those who are involved with cargo tanks where the problems take no prisoners.

However, at the National Tank Truck Carriers Cargo Tank Maintenance Seminar November 12-14, 2007, information was presented to ameliorate some of those concerns.

Ralph Davison of TMR Stainless Inc and Paul Krueger of Stainless Tank and Equipment Co LLC made presentations on these issues at the St Louis, Missouri, meeting.

The good news, Davison said, was that mechanical properties in new stainless steels make them twice as strong as they once were. However, factors such as the type of carrier operation and cycles of cleaning can have a significant effect on the condition of the tank. Many products contain chloride, which enhances the chance for pitting and cracking in stainless steel tanks. Welded areas are particularly susceptible.

Krueger pointed out that pitting usually begins a small but can escalate enough damage to cause a leak, if it is not controlled. Solvents, corn syrups, and oils are among those products that are likely pitting catalysts.

Accidental product mixing is another contributor to problems. One product can lodge in a pit and when another, incompatible product is loaded, a chemical reaction can occur, causing even more damage. An incompatible product also can be introduced during cleaning, Krueger added.

Davison warned that pitting and corrosion areas deteriorate rapidly and may not be discovered for at least 24 hours. Some cracking may not be visible until after leaks have begun. He recommended checking areas where plates and bolts are present and looking for debris. Empty tanks are particularly susceptible to problems and should be evaluated to prevent exposure.

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