Scale inhibition efficiency is determined in bulk jar tests in order to determine a minimum inhibitor concentration (MIC) which gives some acceptable level of inhibition (say 95%). However, this test refers principally to the bulk precipitation of barium mineral scale from solution, rather than its deposition on a surface. The complementary tube blocking test gives some insight into scale adhesion at a surface, but this is a very short residence time test. An experimental study has been conducted to examine the interactions between surface and bulk BaSO4 scaling processes in uninhibited and inhibited supersaturated brines. In this study, precipitation both in bulk and onto a Hastelloy metal surface has been studied in longer term bulk jar tests at various temperatures. It has been demonstrated that the use of PPCA at concentrations beneath the MIC level, as determined by bulk jar tests, can promote surface scaling. This comes about as a result of complex interactions between bulk precipitation and surface scaling processes and these are discussed in this paper.

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