Executive Summary
Background - AS Inc. (ASI) employed Puckorius & Associates, Inc. (P&A) as an independent third-party to test the corrosion inhibiting capabilities of their product, AS-8150, to substantiate successful field results. P&A was to measure corrosion rates of carbon steel, copper and copper alloys under simulated open circulating evaporative cooling water conditions, and to report on their findings. This report presents our findings, conclusions and recommendations as follows:
Conclusions - Our laboratory tests have shown that AS-8150 compared favorably with ortho- phosphate as a corrosion inhibitor for carbon steel. Linear polarization readings on the phosphate system did not reach as Iow a plateau as did the AS-8150-treated system. Mild steel corrosion coupons in the AS-8150 system showed a higher corrosion rate based on metal loss; however, the phosphate-treated coupons showed aggressive attack by gouging and pitting whereas the AS-8150-treated coupons showed more of a general etch. A high initial corrosion rate on the AS-8150-treated coupon as shown on the LPP readings would account for the high weight loss.
Findings and Observations - Linear polarization (LP) readings for "mild" (carbon) steel (MS) on the PO4-treated system started out at 13.64 MPY, jumped to 21.81 MPY for one reading, returned to 14, 15, 12, to a low of 10.21, with an average of 13.81 MPY for a total of 22 days.
The MS LP readings for the AS-8150-treated system started high at 28.82 MPY, dropped to 23.5, 17.0, 15.4, 13.6, 11.0, 9.0, 7.0, 5.8,4.2, to a low of 3.7 MPY and an average of 13.50 MPY (see Tables I and II and Figures 1, 2 and 3) over the same 22 days under the approximately same conditions.
The PO4-treated corrosion coupon showed a weight loss of 2.95% for a calculated corrosion rate of 13.2 MPY, very close to the average of the LP readings. The AS-8150-treated coupon showed a weight loss of 5.64% for a CR of 25.62 MPY, twice the LP average and the PO4-treated coupon MPY.
However, the AS-8150-treated coupon weight loss included the initial high corrosion rate that generally becomes less and less significant the longer the coupon is in the system.
The appearance of the cleaned PO4-treated coupon showed gouging and pitting. The AS-8150- treated coupon showed a "general etch" type of corrosion that is much slower in causing penetration of the metal.
Recommendations - The AS-8150 product should be tested for longer periods as well as against higher dosages of phosphate and also phosphate/zinc programs. Also consider the use of deposit control agents and copper inhibitors as part of a treatment program, particularly with higher hardness waters.
Acknowledgement - P&A wishes to express our appreciation to Bill Stapp for the opportunity to perform the work on this project, and his guidance in outlining the conditions of the operation.