Mechanics Properties Research And Safety Assessment Of Crankshaft On Integral Nature Gas Reciprocating Compressor

The integral reciprocating nature gas compressor, as power equipment of booster transportation, plays a key role in petroleum and natural gas industry, safety operation of compressor is an important guarantee for natural gas production. The mode based on traditional planned maintenance and accident processing is still adopted currently in the management of natural gas compressor. With the increase of service life, the accident rate of assembling units rise, the safe operation of the assembling units is very concerned to the oil and gas field managers. Especially, the old assembling units and its overdue service are very worrying. The overall safety evaluation of compressor is put forward to meet the requirements, based on the thoughts of integral reciprocating compressor’s safety evaluation. This paper proposed a method that combines with the evaluations of both the compressor’s system and components in view of the different proportion of safety and economy of the components, calculated weight coefficient according to the expert scoring and analysis of AHP, overall security evaluation method is established.The gas engine and compressor of integral reciprocating compressor, sharing a crankshaft, are skid-mounted in a base and undertakes the role of power transfer hub. As the core component of compressor, crankshaft bears alternating loads such as time dependent periodic impact and vibration etc. in the operation process of the assembling units. It is just the existence of these alternating loads, leading to the complex deformation such as bending, torsion and bending torsion. The mechanical property of crankshaft not only affects the service life of its own, but also directly affects the safety and stability of the whole unit. Therefore, studies on the mechanical properties of crankshaft and safety evaluations are launched out.This paper studies the mechanical properties analysis and evaluation studies of the crankshaft’s structure of type ZTY470integral reciprocating. And get the external loads such as tangential force, normal force and torque etc. acting on each crankshaft pin through dynamics analysis, thermal analysis and the alternating load bearing on each shaft necks. Mechanics model is simplified according to its actual structure, and the indeterminate equation is established. Static analysis and modal analysis of the integral reciprocating compressor crankshaft are made combined with the finite element software. Based on the modal analysis of the shafting, time history load is applied to analyze the transient response in shaft system. According to the results’analysis, the static intensity and fatigue strength are both checked. Thus, safety evaluation models are established respectively according to the results of whether crankshaft contains crack defect based on the crankshaft NDE. Bulk load spectrum and fatigue life evaluates model of no crack defect crankshaft structure are established based on the S-N curve of materials, the criteria of fatigue life cumulation and field historical load statistics. For those crankshaft structures that contain crack defect engineering process is used to become effective crack size. Residual life evaluation model of crack defect crankshaft structure is established combined the crack propagation rate formula of Paris with the Field strength analysis of stress strain of crack tips and stress intensive factors’ calculation of semi elliptical surface crack etc. In this way, safety assessment and the prediction model of residual life of compressor crankshaft are established respectively under two modes that are with or without the crack defects. In order to revise and perfect the evaluation on crankshaft, tensile test of crankshaft material (yield strength, tensile strength), fatigue strength (fatigue limit, S-N curve) and fracture testing (fracture toughness, crack propagation threshold and the propagation rate of crack stable growth stage) is studied extensively. Structure parameters of crankshaft material safety evaluation are achieved to amend and improve the reliability of the evaluation results. Based on this, for the convenience evaluation on the safety operation of compressor and stress analysis of the crankshaft and its parts, evaluation software CSA Version1.0of natural gas compressor application safety application assessment is compiled.Therefore, methods of integral reciprocating compressor for safety evaluation and the mechanical properties of the crankshaft for studying and safety evaluation come up in this paper to create an effective evaluation measure for the compressor safety management in oil and gas unit. Moreover, it also provides a reasonable theoretical basis for scrapping standards of old set and the set of extended service that are also still in use.