Hydrocarbon scale deposits measurements by neutron moderation and capture gamma methods

Abstract

Nuclear techniques have been used for the detection of hydrocarbon deposits found inside the pipes in oil refinery and chemical plants. Such detection is usually very difficult. The techniques used here were: neutron moderation and capture gamma rays. In the first method, neutrons from 241Am-Be neutron source interact with the scale inside the pipe. Fast neutrons penetrate the pipe wall without significant interaction; they are scattered elastically with the H and C atoms in the hydrocarbon scale and are hereby slowed down. Some of the slowed-down neutrons diffuse backward and are measured by a BF3 slow neutron detector. The detector count rate increases with the scale thickness. In the second method, some of the incident neutrons from the neutron source are captured by the H and C atoms and characteristic gamma quanta are emitted. The quanta are measured by a high purity germanium detector. The detector count rate of any characteristic gamma quantum increases with the amount of scale. Four types of hydrocarbon deposits were investigated: oil refinery scale, asphalt, polyethylene and polyvinylchloride. The neutron moderation technique was the more sensitive method. Here about 0.25 mm change in thickness of asphalt scale can be detected. The capture gamma technique was less sensitive; about 0.8 mm thickness change in asphalt scale was detectable. These techniques are nondestructive. No actual contact takes place with the pipe material. They can function on hot or unprepared pipes and scanning of large area of piping is possible.