Micro cracks have been found near some of the welds on the pipe unit. This paper investigates the root cause of this damage and suggests improvements to prevent such damage from occurring. The investigation includes several simulations using Pipestress and Ansys Mechanical, a welding and materials investigation, and a more theoretical creep investigation using the Larson-Miller parameter. A sensitivity study of the outlet pigtail installation and support configuration is performed as well as a cyclic plastic analysis. A complementary analysis of the catalyst tubes, inlet and outlet system shows that the only areas where the stress and strain indicate an elevated risk of damage are the areas around the ends of the outlet pigtails. Suggested improvements include reconfiguration and load reduction of constant hanger supports, improving welding procedures in order to lower residual stresses and undertake more material and on site investigations to verify causes of failure. ARTICLE HISTORY Received 04.01.2018 Accepted 22.02.2018 Available 15.03.2018

Many effective robot-manipulator control schemes using a disturbance observer have been reported in the literature in the past decades. Besides, the disturbance observer combined with the Kalman filter has attracted the attention of researchers in the field of motion control. The major advantage of a motion control system based on the Kalman filter and disturbance observer is the realization of high robustness against disturbance and parameter variations, effective noise suppression and wideband force sensing. This paper presents a survey of motion control based on the Kalman filter and disturbance observer, which have been previously introduced by the authors. Several control schemes, as well as formulations and applications of the Kalman filter and disturbance observer, are described in the paper. The performance and effectiveness of the control schemes are evaluated to give a useful and comprehensive design of the Kalman filter and disturbance observer in various motion control applications.