Ultrafiltration of effluents from chlorine-free, kraft pulp bleach plants

A description is given of a new form of droplet erosion of titanium condenser tubes. At the sites of maximum impact by wet steam, the tube wall thickness is reduced to zero, and the tubes crack open under pressure of the cooling water. The crack is unbranched and progresses in a stepwise fashion. Along one side of the crack a series of small, circular metallic protrusions develops. Microscopes examination reveals the absence of any corrosion products on the surface. Similarly, no feather-like structure indicative of hydride formation is noted. It is assumed that impact with wet steam produces high-pressure transients and initiates high flow away from the points of impact. Counter-measures against droplet erosion are briefly reviewed and involve the reduction of steam velocity and/or degree of wetness. Plugging of the defected tubes is another practical means, and the use of protective sleeves might also be considered. Retubing with a more erosion-resistant material might present an ultimate, more feasible solution.