Comparison testing was performed to measure the relative corrosion rate of the most commonly used CorrView ^® model in 1-1/2 in. ASTM 1018 steel, and the most commonly installed pipe for HVAC and process water systems - ASTM A53. Testing was performed under water immersion.

     A 1-1/2 in. size standard CorrView ^® corrosion monitor manufactured of ASTM 1018 mild steel was installed into a test assembly comprised of a 3 in. threaded length of ASTM A53 pipe via a 3 x 1-1/2 reducing adaptor. The outer surface of the 3 in. length of pipe was sanded smooth to minimize any error during ultrasonic testing, and to provide a reliable bonding surface.

     An EPDM rubber template having die cut holes precisely matching the ultrasonic probe diameter was bonded onto the pipe using Loctite metal to rubber bonding adhesive - thereby ensuring precice re-orientation of the UT probe on subsequent evaluation. Duct tape was used to hold the template in place while the adhesive cured.

Side View Of Test Assembly

Close-Up View Of Testing Template

     Following a specialized UT testing procedure developed by CVI for using a client's existing pipe as an "ultimate corrosion coupon," repetitive wall thickness measurements and recalibration were performed until three individal measurements produced the same wall thickness value. A total of 15 sets of such precise wall thickness measurements were taken along two separate templates on the pipe, and recorded in a spreadsheet to provide a baseline.

     In addition, 15 wall thickness measurements were performed in a close circular pattern at the innermost 3/8 in. diameter of the front wear surface of CorrView ^® and similarly recorded.

      The test assembly was placed on its closed end and filled with city water. Muriatic acid was added to reduce the pH of the water to approximately 5. Aeration of the solution was added, and the test assembly allowed to remain for a period of time under ambient conditions. Subsequent testing would measure the wall loss of the interior surface of the pipe against the exterior surface of CorrView ^® - both surfaces being subject to essentially identical corrosive conditions.

      Following 39 days of continuous and undisturbed immersion, the solution of rusty water was drained and CorrView ^® removed for re-testing. Ultrasonic thickness measurement was again performed along the same 15 template points, and at the front surface of CorrView ^®.

     The 15 test locations along the ASTM A53 pipe showed a wall loss of between 0.000 in. and 0.002 in., for a calculated average loss of 0.000786 in. or 0.786 thousands. Calculating the wall loss over time it was exposed to the corrosive environment produced a corrosion rate estimate of 7.35 mils per year. Measurement at the same area of CorrView ^® front wear surface produced a wall loss of between 0.000 in. and 0.001 in., for an average thickness measurement of 0.000999 in. or 0.999 thousands. Calculating this wall loss over exposure time then produced an estimated corrosion rate of 9.36 mils per year.

     This represents an approximate 20% difference in reported corrosion rates between CorrView ^® and actual ASTM A53 pipe under identical conditions. We consider such results excellent considering that the difference in true pipe corrosion rate and corrosion coupons are often in error by 10 times or 1,000 percent or more. This is not due to any failure of the corrosion coupons themselves, but due to their placement in an isolated loop where the many other corrosive factors affecting the pipe are excluded from the testing procedure.

     This same testing assembly is currently undergoing exposure for an additional 60 days.