Standard CorrView products are manufactured from ASTM 1018 grade steel, which is the same material typically used in making corrosion coupons for HVAC piping systems. There is unfortunately no direct solid equivalent to ASTM A53, A106, A795 or other piping materials, which we require in bar stock form for machining. Based upon its physical and chemical properties, however, ASTM 1018 mild carbon steel is very similar, and will produce a close simulation of the corrosion activity occurring against mild carbon steel black pipe. Our own experience in ultrasonically testing piping systems has shown corrosion rates to usually fall within a certain range of values. Most piping systems will be comprised of different grades of mild steel, and almost always from multiple manufacturers. Some pipe may be from different countries of origin. Nevertheless, the corrosion rate found when testing all representative areas of pipe is often surprisingly similar. Differences may exist, but are often difficult to illustrate statistically.
A major factor in widening the wall loss characteristics between mild carbon steels is the corrosion rate itself - similar to the relationship which exists with pitting activity. Differences in the inherent corrosion susceptibility of various forms of mild steel piping, which may not be easily identifiable in the field under low corrosion rate conditions, will become increasingly obvious as the corrosion rate increases.
For this exact reason, and based upon the action of the water alone, CorrView will produce the closest estimate to true corrosion rate when under low corrosion rate conditions, and the highest discrepancy under high corrosion rate conditions. Fundamentally, however, CorrView provides a far more representative estimate of corrosion activity simply due to its placement within the piping system. Having the metal wearing surface exposed to the same conditions and influences as the pipe itself far exceeds the significance of any minor difference in corrosion rates between its metal composition and the that of the pipe itself.
Given sufficient ultrasonic testing of a given piping system, and asuming a generally low corrosion rate, results will typically show a uniform measurement of wall loss even though different pipe types and grades from different manufacturers have been used.
For example, the below comparison of measured wall thickness values to original pipe wall shows a very even amount of wall loss, represented by the red, green, and blue bars, to its original thickness, represented by grey. Ultrasonic testing was performed at 40 individual piping locations comprising mostly 12 in. schedule 40 ASTM A53 pipe, as well as 8 in., 6 in. and 2 in. examples, and returned uniformly low corrosion rates of approximately 1 MPY over a period of 31 years. This graph also represents various manufacturers of pipe, as well as the different metal grades ASTM A53 and A135.
Our own corrosion studies have proven this same relationship. Comparing CorrView products to both corrosion coupons and samples of actual ASTM A53, A106, A135, and A795 steel pipe has shown a strong similarity in result. The below documentation is offered from two separate corrosion studies, with additional testing in progress.
We present below a series of corrosion comparison tests between CorrView and common piping grades used in HVAC and fire installations. An explanation of testing set-up, procedure used, and a detailed review of the results for each metal sample is provided. Each series of tests includes photographs of the test specimins before and after exposure, as well as a statistical and graphical summary of measured corrosion rates.
Further comparison corrosion testing is planned. Please check back for additional information.
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