Oil and gas pipeline corrosion online monitor

Abstract

The invention discloses an oil and gas pipeline corrosion online monitor, which measures the corrosion of an oil and gas pipeline by an electric-resistivity method. The monitor comprises a resistance probe, a measurement circuit and a measurement data processing unit, wherein the resistance probe (1) comprises waterproof jacks (12), a sealing screw thread (13) and a probe shell (14); the upper part of the sealing screw thread (13) is connected with the waterproof jacks (12), while a lower part is connected with the probe shell (14) made from stainless steel; a built-in sensing element (15), which is a reference resistor Rf, and a built-in thermal resistor Rt (10) are arranged in the probe shell (14), and are positioned in an identical temperature environment; an exposed sensing element (16), which is a measured resistor Rx, is arranged out of the probe shell (14), and is directly exposed in a corrosion environment in the pipeline; and the built-in sensing element (15) and the exposed sensing element (16) are made from an identical material and have an identical temperature coefficient. The resistance corrosion monitoring device of the invention has the characteristics of quick response, continuous testing capacity, the capacity of sensitively detecting the small change of a corrosion state in the pipeline, high reliability and high data reproducibility.

Description

technical field [0001] The invention relates to the field of on-line corrosion monitoring of oil and gas pipelines, in particular to an on-line corrosion monitor for oil and gas pipeline resistance based on temperature compensation and contact potential compensation. High-precision online corrosion monitoring for any mixed medium of oil, water and gas. Background technique [0002] With the development of large-scale oil and gas fields in my country, especially the continuous exploitation of high-pressure sulfur-containing and carbon dioxide-containing natural gas, higher requirements have been put forward for the safety of oil and gas fields. Corrosion monitoring, as a basic work of corrosion protection, has increasingly received business attention and attention. The resistance probe corrosion monitoring technology is to realize the online monitoring of the corrosion rate of the metal in the process medium by measuring the change of the resistance value of the metal sensiti...

AI Technical Summary

Problems solved by technology

[0003]At present, the resistance corrosion monitoring at home and abroad does not take into account the influence of temperature difference potential and contact potential on the sensitive components of the resistance probe. The influence of thermoelectric potential and contact potential is small

However, the oil and gas pipeline is a high-pressure system, and the process of natural gas or production fluid flowing from the wellhead to the station is greatly affected by the formation environment and surface temperature changes, and the measurement accuracy of the corrosion rate drops sharply due to temperature fluctuations

The U.S. invention patents US5,446,369 and US6,556,027 are both inventions on resistance probe corrosion monitoring instruments, but neither of them pointed out the influence of temperature on the measurement results, nor did they use automatic temperature compensation technology. On-line resistance corrosion monitors, the application results of these corrosion monitors in oil and gas field corrosion monitoring show that the reproducibility of the measurement results and the stability of the equipment have not been solved, and the measurement accuracy is even only 1 / 500 of the service life of the probe sensitive components. The reason is that the temperature difference effect brought by the contact potential inside the resistance probe greatly interferes with corrosion monitoring, and it is difficult to ensure the accuracy of oil and gas pipeline corrosion monitoring by completely relying on the built-in reference resistor Rf for temperature effect compensation , especially when the corrosion rate is low, this effect renders the measurement unusable

The patent document (ZL200820108634.9) also discloses a resistance probe corrosion monitoring instrument, which reduces the interference caused by the internal contact potential of the probe to the corrosion measurement by using the method of alternating current excitation, but the monitoring instrument in this document Rely on the built-in reference resistor Rf for temperature effect compensation, due to the small resistance of Rf (<10mΩ), the temperature measurement is greatly affected by the contact resistance, and the measured temperature can be reproduced Low stability, which restricts the improvement of corrosion measurement accuracy

In addition, the international magnetic resistance probe corrosion monitor also has the disadvantage that the measurement results are greatly affected by temperature. Field measurements show that in natural gas pipelines with large temperature fluctuations, its measurement accuracy is even lower than that of resistance probes.

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