TRACER APPLICATIONS IN INTEGRITY ASSESSMENTS FOR TANKS, TERMINALS AND TRANSPORTATION PIPING

摘要

The last revision of the American Petroleum Institute (API) guideline for the inspection of facility piping (API 570) includes tracer leak detection methods as an alternative to hydrostatic testing of buried pipelines. Tracer testing is a method in which a small concentration of a chemical label is added to the fluid inside a pipe. If a leak is present, analysis of air samples collected outside of the pipeline shows an increase in the concentration of the chemical vapor above background. Tracer test methods have been evaluated and validated by many studies. A summary of the cumulative data is described. Cumulatively, two hundred and one leaks were simulated under a variety of conditions. All but one of the leaks was detected. Of the one hundred and one control events in which no leak-indicating tracer was released, there was one false indication of the presence of the tracer. The autopsy of this event revealed that the false detection was due to operator error. Individual leaks have been located in large diameter pipelines regulated by the United Sates Department of Transportation. A case study is summarized in which a single leak in a forty-kilometer section of 0.4-meter diameter piping was located. This was a newly constructed yet to be commissioned pipeline built for the transport of natural gas. The single leak was located during the first day of sampling. Large refineries have used tracer methods to meet regulatory or facility inspection requirements. Refineries and chemical plants have used developing and established tracer test methods to meet regulatory requirements and to explore new ways of augmenting Asset Integrity Management programs. A six-year tightness testing program for a refinery/chemical plant facility including fifty kilometers of facility piping is summarized. During the most recent test season at the chemical plant, the frequency of detection of small leaks was one leak per kilometer of piping. None of the leaks detected during the six-year project accounted for the amount of petroleum product below ground surface. Significant releases at this facility were attributed to aboveground storage tanks. A final case study is included in which the location of a leak in an operating refinery pipeline and an associated aboveground tanks is summarized. The leak detection and location project was combined with a field evaluation of a new leak detection method for operating pipelines in which below-ground leaks are detected in samples collected above the ground. The leak in the supply line was located within the first twenty-four hours after the addition of the leak indicting tracer. Another leak through the floor of an associated aboveground storage tank was also detected on the day after the tracer was added by the presence of the leak detection tracer additive in samples collected below the tank. The tank also remained in continuous operation. Advantages of the test include: continuous operation of the piping and tanks during the test, avoidance any need to remove product, replace the product with water, treat the contaminated water or dispose of it. The use of a chemical tracer test method, designed for operating facility tanks and piping can in many instances serve well as an alternative to hydrostatic testing for meeting API 570 standards.