A portable gamma ray tomography system has been designed to investigate geothermal power plant pipe scaling. Furthermore, the system could be applied to diagnose industrial processes unit such as pipeline, heat exchanger, and so on. The system consists of mechanical parts, computerized controlled module, a gamma ray source (80 mCi of Cs-137), a scintillation detector NaI(Tl), data acquisition and computer. The mechanical part was designed to meet the portability standard of industrial processes unit such as dimension, position, material type, etc. The investigated object is scanned an in two ways (translation and rotation) of ray transmission to capture attenuated radiation automatically. The result of object investigation is displayed in computer directly using a proposed reconstruction image technique. The reconstruction image was performed using Filtered Back Projection (FBP) algorithm and optimized with the weighted correction factor for each pixel. The weighted correction factor was computed based on the modeling of gamma ray transmission in selected mechanical system. In evaluating the proposed system, experiments were performed using a geothermal power plant pipe that has 275 mm diameter within known scaling form. Steady state water was flowed inside the pipe to simulate multiphase condition in geothermal power plant pipeline. Scanning configuration was set up to 4 mm steps and 32 projections. Based on the chosen evaluation criteria, the reconstruction image of the proposed system shows good result. Finally, the proposed portable gamma ray tomography system is suitable to industrial applications due to its portability and accuracy in detecting the form of pipeline scaling.