Analisa Kegagalan pada Patahnya Sambungan Las dalam Sistem Instrumentasi Katup Pengaman Tekanan Kerja

Failure analysis is carried out by applying a series of inspections and tests on the welding joints of tubes that used in theoil and gas industrial equipment. Failure in the form of a fracture was found in the tube which is part of working pressure safety valve instrumentation system. Observation with a microscope at low magnification shows that the crack initiated from the outer side of the tube wall with morphology of fatigue cracks pattern. Chemical composition test shows that the tube material is stainless steel type 316L. Analysis using a scanning electron microscope on the fracture surface proves that the fracture mechanism is a brittle fracture that propagates at the grain boundaries. Based on observation, cracks in the tube connection occure due to dynamic loads under operational condition. The main cause of dynamic loads is the vibration phenomenon arising from the opening and closing mechanisms of the working pressure safety valve. The phenomenon of vibration that occurs in the tube material causes fatigue cracks in the welding joint area which continues to propagate and then leaves a cross sectional area that is no longer able to withstand the load and eventually leads to system failure. Several recommendation are given as a method of prevention, especialy failure in welded joints of tubes that have small diameters