The soil corrosion rate test methods

Oil and gas pipeline corrosion in the soil is a very slow process, and how to obtain reliable corrosion rate data in a short time, is carried pipeline corrosion life prediction of an important basic research.

Corrosive soil evaluation, the widespread adoption of on-site underground sheet test method, and then the corrosion rate was measured by weight loss method. Because of soil corrosion of buried patch test cycle is very long, generally 10 to 30 years. Therefore, to obtain reliable within a short time of soil erosion rate data, is corrosion of soil have been pursuing the goal. With the development of electro chemical techniques, soil erosion in many studies using the linear polarization method or electro chemical polarization scanning method, but rarely actually buried sheet corrosion rate results were compared. Typically, the corrosion rate measured by electro chemical technique uniform corrosion rate, localized corrosion of the pipe does not reflect the present in the service process. Galvanic or electrolytic corrosion accelerated corrosion test is Soil research methods commonly used, but due to the strong electro chemical polarization will cover the role of various factors in soil composition on the corrosion process, therefore, the resulting corrosion of the law is not necessarily realistic pipeline corrosion.

Pipeline corrosion is produced naturally in the soil, the study naturally in the soil pipe corrosion is realistic corrosion pipeline. Pipe corrosion in natural soil is a very slow process, only the accumulation of corrosion to a certain extent, in order to measure the corrosion rate. Currently resistance probe can be used within a few days to detect corrosion under natural conditions the corrosion rate at 0.1 ~ 0.2mm / a the amount of change, in order to achieve this precision, cross-sectional area ofthe test piece used to be very small, At the same time to improve the resistance of the specimen, usually metal filaments, a diameter of 2mm or less. The presence of the specimen resistance probes used question three aspects, one manufacturing difficulties; the second is the specimen is too small, the temperature effect on the large specimen resistance, corrosion rate measured fluctuate with changes in temperature, often have The corrosion rate of less than reliable; it is difficult to reflect the actual shape of three corrosion. Pipeline corrosion life prediction of corrosion rate required field pipeline corrosion process must conform, to reflect the specific circumstances of the actual corrosion. In this sense, accelerated corrosion test is not practical, and buried patch test is required. However, the specimen buried soil corrosion sheet used, taking into account the corrosion morphology analysis should have a larger cross-sectional area, taking into account the resistance measurement should have a smaller cross-sectional area.