NACE Test Method TM0172, “Determining the Corrosive Properties of Petroleum Cargoes” [1] is a simple and valuable test to determine whether refined products, such as motor fuels, are sufficiently dosed with inhibitor to prevent corrosion in the event that water enters the product stream. This test is based on optical examination of the area of the coupon affected by corrosion after a specified exposure to a hydrocarbon/water mixture. Letter “grades” from A to E are subjectively determined by the technician performing the test. Experience has shown that if enough inhibitor is present to produce B+ or better results as defined in this standard, general corrosion in flowing pipelines may be controlled. Grade “B+” or better represents a practical absence of corrosion (less than 5% area).
For the purposes of confirming a practical absence of corrosion, the subjective evaluation by a technician is adequate. However, as this test may be applied to less refined, uninhibited products where larger areas of corrosion may be observed, the letter grading does not provide discrimination within very wide ranges of corrosion affected area (20–25% of coupon area). Pipeline integrity managers interested in the relative susceptibility to internal corrosion caused by uninhibited hydrocarbons may be interested a higher level of corrosion discrimination and precision.
Enbridge Pipelines proposed a digital image analysis technique in 2009, and this technique has been developed, refined, and successfully employed by Alberta Innovates - Technology Futures (AITF). This paper discusses the development of this technique, as well as comparative results using both the original letter grading system and the digital analysis method. Other observations regarding the application of the TM0172 method on a variety of hydrocarbon categories are presented.
