Determination of scale deposition in a flare line by neutron back-diffusion

Flares are used in the oil industry and other industries to dispose of waste gasses by burning. Damaged or blocked flares can lead to incomplete combustion and the release of contaminating gasses into the atmosphere. In this study, the neutron back-diffusion technique was used to measure the scale inside a flare stack. The neutron source employed was ²⁴¹Am-Be with an activity of 1.11 × 10¹¹ Bq (3 Ci), and a BF₃ slow neutron detector. Scanning was conducted for scale in the stack at a refinery. Back-diffused neutron counts were doubled when moving from no scale to a scale thickness of about 17 cm. The scale thickness measured up to 20 cm and a change in the thickness of about 0.25 cm could be detected in a counting time of 1 min. The counting system weighed about 3 kg and it allowed scanning at a high stack elevation. The source employed yielded a total dose of 0.12 mSv h^-1 at 1 m, which is significantly smaller than the doses from sources used in industrial radiography.