TP48 – Materials for pumping seawater and media with high chloride content

The problems associated with the choice of materials for pumping aggressive media are reviewed, with particular focus on those media containing hydrogen sulphide. The characteristics of the corrosion forms occurring during the pumping of such media govern the measuring techniques and instrumentation for tracking these phenomena. In particular a high-velocity test rig developed is described.

On the strength of their own measurements as well as data from the literature, the authors discuss the behaviour of pump materials in such media. It is shown that the choice of material depends largely on the composition of the medium, in particular the HiS content and the combination H2S + air.

In pure seawater or in pure chloride-containing media, the differences between the materials examined are relatively small. Austenitic-ferritic steels perform especially well in such media.

In the presence of hydrogen sulphide the differences between the individual materials become great, and may reach a factor of 10×4 with high concentrations of H2S. Special materials are needed for pumping such media. Of particular interest is the presentation of data that supports the addition of Cu into alloys to improve corrosion / erosion corrosion – in both 13%Cr and 25%Cr alloys, the Cu-containing variants significantly outperformed the plain alloys. Ferralium 255 is widely selected for the manufacture of pump shafts for this very reason. 

Finally it is demonstrated that in media with high contents of hydrogen sulphide the attack is initiated by pitting, even at very high flow velocities.