EXISTING CONDITION

The visual appearance of the water in the East Temperature Control Unit (TCU) was distressing. There was an obvious corrosion mechanism occurring, which has resulted in a significant amount of dissolved and particulate iron in the bulk water solution. The East TCU differs from the West TCU in that the hot (140ºF) process water returns to the sump prior to being cooled by the heat exchanger. The West TCU process water is cooled before being directed to the stump.

The East TCU differs from the West TCU in that the hot (140ºF) process water returns to the sump prior to being cooled by the heat exchanger. The West TCU process water is cooled before being directed to the stump.

Both TCU utilized soft water makeup, a molybdate corrosion inhibitor, and a non-oxidizing biocide. Due to the high water temperature in the East TCU, and the fact that the sump water is aerated, it was suspected that the corrosion mechanism was oxygen-pitting corrosion caused by the liberation of dissolved oxygen in the presence of the bulk high temperature water. To confirm this a corrator was used to provide instantaneous corrosion results. This device measures general and pitting corrosion. Our strategy was to install the corrator in the corrosion coupon by-pass rack and evaluate the corrosion potentials, as they existed and after the addition of a
Cortec’s VpCI® corrosion inhibitor.

Approximately 2/3 of a gallon of the new corrosion inhibitor (S-69 P) was added to the sump. S-69 P had a foaming tendency that was addressed by adding some antifoam to the East TCU sump. The corrator probe was allowed to stabilize for 24 hours prior to obtaining the new general and pitting corrosion rate readings. The corrosion rate readings after the addition of S-69 P are as follows:

The East TCU had the following characteristics prior to testing:

pH:
9.09

Molybdate Concentration: Molybdate Concentration:
1,160ppm

Conductivity: Conductivity:
3,200µS

General Corrosion: General Corrosion:
0.2 – 0.5 MPY
Pitting Corrosion: Pitting Corrosion:
0.2 MPY

There was a significant decrease in the pitting corrosion potential after 24 hours since addition of S-69 P. Based on these preliminary results, a new product was formulated based on Cortec’s S-69 P corrosion inhibitor used in this test.

After filtering the iron fouling in the loops and flushing out the old water inhibited with molybdate the loop was recharged with fresh water inhibited with Cortec’s Vapor phase Corrosion Inhibitor S-69 P.

After two years of continued implementation of Cortec’s S-69 P based formulation has resulted in acceptable corrosion rates to customer’s satisfaction. Currently this formulation is utilized in both East & West TCUs.