Eddy current analysis of shipped stainless steel heat exchanger bundle

In this paper, we present the results of a failure analysis done on new heat exchanger tubes, which shows loss of thickness during a EC inspection to stablish a prior loss of thickness base line aiming guarantee fitness for service during its working life. The root cause analysis indicates that there is intergranular corrosion due a differential concentration caused by seawater evaporation inside the tubes during the ship transit from the port of origin in China to the destination port in Brazil.

The intergranular corrosion depth showed by root cause failure analysis is smaller than that showed by EC inspection. We attribute the EC inspection results deviation to a tube magnetisation due to mechanical stress and to a secondary phase due to an incomplete solubilisation after tube conforming and welding.

Traditionally, these tubes are visually inspected and deemed acceptable but our conclusions reveal that eddy current testing is capable of detecting some corrosion anomalies which makes the tubes unfit for service.