Protective lacquer layer applied inside pipeline - after phosphating with alkanoic phosphoric acid, leaving dry surface taking lacquer well

摘要

Process of applying a protective layer to the inside surface of a pipeline comprises: (i) removing contamination; (ii) phosphating with a soln. of H3PO4 in a 1-3C aliphatic alcohol; and (iii) applying a layer of lacquer. Step (ii) may be effected in several stages, of which only the last need use a soln. of H3PO4 in an alcohol, pref. methanol. (The preceding stages may use e.g. aq. H3PO4). The concn. of H3PO4 in methanol is pref. 5-20 (esp. 7-12) wt.%. The contact time of the soln. with the inside pipe surface is pref. 0.25-2 (esp. 0.5-1.5) hr. Contact time can be controlled by enclosing a slug of H3PO4 soln. between two pigs, and moving the combination along at the required rate by applying pressure to one of the pigs. The lacquer used usually comprises an epoxy or polyurethane resin.