Abstract
Recently an European funded project aiming to develop a standard test method for qualifying stainless steels for crevice corrosion in seawater. In addition a new synthetic seawater has been developed with biological properties simulating natural seawater as a reproducible crevice former for plate material. A so-called Round-Robin test has been carried out in both the new synthetic seawater composition as well as in natural seawater. As a part of this project the development of a crevice corrosion test method for tubes has been included.
Until today there has, to the author’s knowledge, not existed a well-defined method for crevice corrosion testing of tubes in seawater has been available. In order to achieve similar crevice conditions on a tube as for a plate, finite element modeling (FEM) was used. The clamping force that gives similar conditions inside a crevice on a tube as it does for a plate crevice was determined for several tube dimensions. This resulted in a calibration curve of the clamping force versus the tube diameter. For a standard duplex stainless steel, UNS S31803, preliminary crevice corrosion testing was made on tubes according to the calibration curve and the results were compared to results from plate crevices in synthetic seawater from Round-Robin test program. For two laboratories crevice corrosion was found to initiate at 30°C, which is similar that observed for testing plate material of the same grade.
