Failure Analysis in the Pipe of Heat Recovery Steam Boiler Generator (HRSG) at the Gas Refinery
Husaini*, Faleri Armia, Nurdin Ali, and Teuku Edisah Putra
Computational Mechanics Laboratory
Department of Mechanical Engineering, Universitas Syiah Kuala
Jl. Tgk. Syech Abdurrauf No. 7, Darussalam - Banda Aceh 23111, Indonesia
*husainiftm[at]unsyiah.ac.id
Abstract
As it is known that the failure of the boiler pipe often occurs on the super heater pipe of a Steam Recovery Boiler Pipe Generator (HRSG). Super heater is a component where water vapor is heated with a temperature around 816 ° C to produce enough steam to drive a generator at a steam power plant. The purpose of this study is to analyze the failure of the super heater pipe of the HRSG which has broken. This research starts from visual observation of broken pipes. Further information is also sought about the operating conditions when the pipe breaks. Then a laboratory test was carried out to determine the chemical composition of the HRSG boiler pipe material. Moreover the hardness testing was conducted by using Rockwell Hardness Tester ZHR 4150AK/BK Zwick Roell. And then the micro-structure was observed by using Microscope Optic Olympus GX71. SEM (Scanning Electron Microscope) observation on the fracture surface was also conducted to find the initial crack. From the results of chemical composition testing, it was found that the material of super heater pipe is made of carbon steel materials ASME SA 178. Metallographic results show that the micro-structure of this material is Ferrite - Pearlite. The result of hardness test shows that the surface area of the pipe is not broken has an average hardness of 25.3 HRB and the hardness of the broken surface has an average hardness of about 15.4 HRB. From the SEM observation, it is known that the failure occurs in a ductile fracture due to inter granular crack occurs on on the fracture surface of the pipe. The presence of deformation (creep) seen on the super heater pipes is due to operating at high temperatures and pressures with long operating time. This condition causes the thickness of the pipe to be depleted and also the presence of pitting corrosion on the inside of the pipe so that it breaks due to crack propagation which penetrates the wall of the pipe until it breaks because the material is no longer able to withstand the steam pressure inside the pipe. To find the magnitude of the stress intensity factor around the tip of the crack is conducted using Finite Element Analysis. From the finite element analysis results, it was found that the stress intensity factor, KI is about 59.49 MPa√mm which occurred in the initial defect area was greater than the value of the fracture toughness of the material KIC is about 49.15 MPa√mm (KI > KIC). This condition indicates that the crack propagation occurred through the pipe wall which caused the boiler pipe to break.
Keywords: Super heater; Fracture; Carbon steel; Hardness; HRSG
Topic: Mechanical Engineering