All it takes is one contact to cause extensive damage
Many problems with corrosion damage in industry can be prevented or detected in time thanks to relatively simple techniques. One way is to conduct electrical contact measurements and determine whether there are galvanic currents between rebar and other structures.
Västblekinge Miljö is a municipal company engaged in waste management. Their facility has two digestion tanks, operation since 2013. But only after three months the pressure reduced dramatically in one tank.
“An investigation followed to find the cause, but initially we were stumped. The pipes were changed to unpainted carbon steel pipes, but the problems continued,” says researcher Bror Sederholm.
One point of contact caused the problem
After three years, the pressure fell again and Swerea was commissioned to re-examine the facility together with Västblekinge Miljö and the previously involved consultants. Holes in the pipes were found again and new analyses were made of the microstructure and thickness of the tubes, among other things.
“After further measurements, we managed to locate the problem – a point of contact between a heating pipe and the rebar. When removed the point of contact and the galvanic currents disappeared. To be safe, the pipe was changed again and chloride analyses were made. They showed low chloride content in the concrete where it was reinforced, implying negligible corrosion risk during the next 50 years. That is, no more stops caused by corrosion should be expected in the next few decades,” said Bror Sederholm.
Thorough investigation paid off
Lessons learned are that a single contact point can cause extensive damage. Also to be very careful when installing steel pipes in corrosive environments and to measure continuously and with several methods so that galvanic currents are detected early.