A. Balamesh, F.A. Abolaban, S. Abdul-Majid
King Abdulaziz University,
Keywords: corrosion, insulation, inspection
Summary:Corrosion under insulation (CUI) inspection is a major problem in the power, petrochemical, desalination and other big industrial plants. Millions of dollars are spent every year due to failures in pipes and tanks as a result of corrosion failure not detected on time. An ideal inspection technique should function on-line because plant shutdown is extremely costly; a one day of a plant shut down cost millions of dollars. It also should work without removal of insulation, a very expensive process and may reach $130 million per year. Currently there is no successful technique for CUI inspection. The ultrasonic technique needs removal of insulation, x-ray direct radiography fails because radiation is not energetic enough to produce image, while gamma radiography is extremely hazardous and bulky and fail to measure corrosion in tanks and reservoirs. The technique we developed is one-side imaging, can function on-line without removal of insulation, can measure corrosion in tanks and use very low radioactivity of about 10,000 times that of gamma radiography. Accordingly, it can save huge amounts of money in CUI inspections. Moreover, its weight is only few kilograms, about 1% of gamma radiography, can be manually or automatically operated and cost about 5% of gamma radiography. In this technique a gamma ray Compton backscatter is used for imaging defects and thickness variations in insulated pipes and tanks. The scattered radiation is measured by a scintillation detector that scans the object using a two-dimensional mechanical scanning system. The gamma spectrum was displayed with a multichannel analyzer, and the energy window width was selected so that only Compton single scatter counts were measured. Images were constructed using the LabVIEW or Matlab computer programs. Successful images of defects in the object under the insulation were obtained, and the system was found to be able to detect 0.5 mm wall thickness changes in large pipes with walls more than 15 mm thick. Low activity sources of 108 Bq (a few mCi) were used, and the dose rate near the surface is four orders of magnitude lower than conventional industrial radiography sources, permitting it to be much safer. The technique can work for metal, plastic or ceramic objects. A USD patent was granted (US Patent number: 8767912, July 1, 2014).