Utilizing sensitivity of the radioactive tracers, it is possible to detect leakages in technological equipment or pipes far earlier than appearance of the leaked materials would be observed in the contaminated component or would endanger product quality or cause any technical risk. For instance, if there is a leakage in a heat exchanger, where migration of the cooling agent into the cooled material (e. g., product) causes obvious deterioration in the product quality, this contamination is detected using traditionally applied analytical methods only if the rate of leakage exceeds detection limits of the given method. With radioactive tracers, however, leakages even in the very early phase can be detected and eliminated readily (Figure 11.1).

Among the radiotracer leakage test methods, leak detection and leak localization on oil pipelines have the utmost importance. Pipelines generally run underground.

For a radiotracer test, NH^Br solution is injected into the streaming oil at a pres­sure upgrading station. This radioactive tracer is miscible with the oil, so the streaming oil will incorporate and transport the radioactive tracer along the pipe­line. At those spots where the pipeline leaks, oil seeps out to the surrounding soil layers. When the radioactive cloud reaches these spots, together with the oil, a small amount of radioactive tracer will also get into the soil. The NH482Br tracer is well adsorbed in the soil. The nonradioactive natural oil stream fills up the pipeline gradually, washing the radioactive cloud into a huge storage tank. But the small radioactive contamination remains in the soil at the location of the leak. With suitable detectors, its location and intensity can be determined.

In the past, the location of the radioactive spot was identified with hand detec­tors by walking along the pipeline on the surface. For this technique, high radio­tracer activities (10—100 GBq) were necessary because soil layers covering the pipeline absorbed a considerable portion of the radiation (Figure 11.2). Today, new detectors have been developed that are built into so-called pigs passing together with the oil stream inside the pipeline, and they both detect radioactivity and mea­sure the distance. Based on this modern detection technique, count versus distance plots provide information on the location of leakage, and the detected counts give

the rate of leakage. For this detection technique, 1 — 10 GBq of radiotracer is suffi­cient for a leakage test (Figure 11.3).

Further examples of leakage tests that were carried out using the radioisotope tracer technique include the following:

• Localization of leaking spots on high-voltage electric cables under gas pressure.

• Localization of leaks in gas-filled telecommunication cables.

• Localization of damaged spots on bitumen-lined concrete tanks.