THE INFLUENCE OF THERMAL LOADING ON THE LEAK TIGHTNESS BEHAVIOUR OF HORIZONTALLY SPLIT CENTRIFUGAL COMPRESSORS

LectureFor the purpose of maintenance requirements or for some applications in the chemical industry (for instance chlorine) the centrifugal compressor must be designed with a horizontally (axially) split casing. Beyond the decision about the type of manufacturing (cast or welded) or about the material selection one of the utmost issues regarding the design of the compressor lies in the leak tightness of the flanges. The design of the compressor casing needs detailed checking for tightness. In order to ensure a proper design with respect to integrity of stress and tightness under test and operating conditions several FE Analyses and resulting criteria have been developed by the OEMs. Furthermore in order to demonstrate the leak tightness the casing is subjected to a hydrostatic test prior to the assembly of the inner parts and rotor. According the API specification a hydrostatic pressure of at least 1.5 times maximum design pressure is applied. This standard procedure is usually considered to be sufficient for demonstrating the casing integrity, the tightness in operation and to check the accuracy of the FE analysis. However some applications require the use of several sections (consisting of some stages) inside one casing. According to the stage configuration hot and cold casing sections might be close to each other. In operation the compressor casing is subjected not only to pressure but also to thermal loading. These potential high temperature gradients can considerably influence the compressor behaviour regarding its tightness. The conventional hydrostatic test can even be less critical than at some particular operating conditions of the compressor on site. This paper describes some experiences of the author’s company with this type of compressors and the performed calculations. Different configurations are analysed and compared between each others. The paper shows the steps for the optimization of casings in order to develop an appropriate split line flange design supported by FE calculations. Some examples of different casing concepts are shown and discussed. At last the paper highlights some decisive issues which influence the tightness of compressor like: - Design of inner casing - Arrangement of sections - Geometry of flange - Design and arrangement of bolts

Large Vibrations on Centrifugal Compressor Caused by Inappropriate Operation During Mechanical Running Test

Case StudiesDuring the mechanical test of a centrifugal compressor, the rotor experienced a sudden increase of the radial vibrations. After re-start, the compressor showed unacceptably high vibrations. The RCA revealed: The vibrations increased while running at trip speed close to surge. The shrink of the impeller, which had moved on the shaft, was too low to withstand these conditions. The impeller was removed and the shrink increased. After reassembly no high vibration appeared at trip speed anymore. Generally, the operation time at trip speed shall be reduced to its minimum and shall not be considered as “normal” continuous operation

Large Vibrations on a Centrifugal Compressor Caused by High Windage Heating on a Flexible Coupling–Root Cause Analysis and Solutions

Case StudyBackground: 2 parallel trains consisting of a Low Pressure (LPC) and High Pressure (HPC) compressors were supplied for an offshore reinjection application near the coast of Angola. During the commissioning on site large lateral vibrations were observed at both units on the Bearings “Drive-End”of the Pinion and “Drive-End”of the LPC. Several balancing runs of the trains on site were necessary to operate both units and allow for injection gas. To avoid repeated field balancing (if coupling or rotor must be removed/reinstalled during future maintenance) the coupling and oil system needed to be re-designed

THE INFLUENCE OF THERMAL LOADING ON THE LEAK TIGHTNESS BEHAVIOUR OF HORIZONTALLY SPLIT CENTRIFUGAL COMPRESSORS

LectureFor the purpose of maintenance requirements or for some applications in the chemical industry (for instance chlorine) the centrifugal compressor must be designed with a horizontally (axially) split casing. Beyond the decision about the type of manufacturing (cast or welded) or about the material selection one of the utmost issues regarding the design of the compressor lies in the leak tightness of the flanges. The design of the compressor casing needs detailed checking for tightness. In order to ensure a proper design with respect to integrity of stress and tightness under test and operating conditions several FE Analyses and resulting criteria have been developed by the OEMs. Furthermore in order to demonstrate the leak tightness the casing is subjected to a hydrostatic test prior to the assembly of the inner parts and rotor. According the API specification a hydrostatic pressure of at least 1.5 times maximum design pressure is applied. This standard procedure is usually considered to be sufficient for demonstrating the casing integrity, the tightness in operation and to check the accuracy of the FE analysis. However some applications require the use of several sections (consisting of some stages) inside one casing. According to the stage configuration hot and cold casing sections might be close to each other. In operation the compressor casing is subjected not only to pressure but also to thermal loading. These potential high temperature gradients can considerably influence the compressor behaviour regarding its tightness. The conventional hydrostatic test can even be less critical than at some particular operating conditions of the compressor on site. This paper describes some experiences of the author’s company with this type of compressors and the performed calculations. Different configurations are analysed and compared between each others. The paper shows the steps for the optimization of casings in order to develop an appropriate split line flange design supported by FE calculations. Some examples of different casing concepts are shown and discussed. At last the paper highlights some decisive issues which influence the tightness of compressor like: - Design of inner casing - Arrangement of sections - Geometry of flange - Design and arrangement of bolts

Unexpected Vibration on a Centrifugal Compressor Caused by Vibration Probe Support

Case StudiesDuring the commissioning of a Main Air Compressor in an Air Separation Unit, the rotor showed increased radial vibrations at the Non-Drive End probe. The RCA revealed: The vibration resulted from the excitation of a natural frequency of the vibration probe support, triggered by the pressure fluctuation at the suction of the 11 blades-impeller. The probe support was redesigned to increase its stiffness in order to shift the natural frequency. After replacement of the support, no particular vibration appeared anymore. Generally: The vibration probe support requires careful attention, especially if the machine is standardized for a very large operation speed range

Large Vibrations on Centrifugal Compressor Caused by Inappropriate Operation During Mechanical Running Test

Case StudiesDuring the mechanical test of a centrifugal compressor, the rotor experienced a sudden increase of the radial vibrations. After re-start, the compressor showed unacceptably high vibrations. The RCA revealed: The vibrations increased while running at trip speed close to surge. The shrink of the impeller, which had moved on the shaft, was too low to withstand these conditions. The impeller was removed and the shrink increased. After reassembly no high vibration appeared at trip speed anymore. Generally, the operation time at trip speed shall be reduced to its minimum and shall not be considered as “normal” continuous operation

Blade Failure on an Axial Compressor Caused by Unexpected Operating at Choke

Case Stud

Large Vibrations on a Centrifugal Compressor Caused by High Windage Heating on a Flexible Coupling–Root Cause Analysis and Solutions

Case StudyBackground: 2 parallel trains consisting of a Low Pressure (LPC) and High Pressure (HPC) compressors were supplied for an offshore reinjection application near the coast of Angola. During the commissioning on site large lateral vibrations were observed at both units on the Bearings “Drive-End”of the Pinion and “Drive-End”of the LPC. Several balancing runs of the trains on site were necessary to operate both units and allow for injection gas. To avoid repeated field balancing (if coupling or rotor must be removed/reinstalled during future maintenance) the coupling and oil system needed to be re-designed

Comparison Of Different Variable Speed Compression Train Configurations With Respect To Rotordynamic Stability And Torsional Integrity

TutorialWherever a variable speed gas compression train is needed for Oil & Gas upstream applications as well as for gas storage applications the primary decision has to be made between a gas turbine driver and an electric motor controlled by a variable frequency drive (VFD). A second decision has to be made between a high speed direct driven train and a low speed driver (gas turbine or motor) driving the compressor via a speed increasing gear. Finally it has to be decided whether a classical, oil lubricated train arrangement shall be used or if a high speed, oil-free, magnetic bearing levitated train configuration shall be chosen. With these three major decisions a variety of different train configurations are possible. They differ from each other in many technical aspects and therefore have strengths and weaknesses which can be rated in order to facilitate the evaluation of the optimum equipment configuration for a certain application. This paper specifically concentrates on the comparison of rotordynamic key figures like the logarithmic decrement (damping) of the lowest bending mode, the presence of overhung coupling modes within the speed range or the presence of torsional critical speeds which can be excited within the speed range and which therefore might adversely affect the integrity of the train components. The evaluated configurations include modern hermetically sealed, oil-free, magnetic bearing levitated compressor designs. Based on these key figures this paper will benchmark the rotordynamic robustness as well as the operational safety of the investigated train configurations

CS06: Inappropriate Operation During Mechanical Running Test of a High-Pressure Compressor Equipped With an Hole Pattern Seal

Case Studies During the mechanical running test of a HP centrifugal compressor, the rotorexperienced a sudden increase of the radial vibrations During run-down thecompressor experienced a trip and high vibrations were recorded The RCA revealed: for the manufactured clearance of the hole pattern seal thetemperature level and the gradient of the pressure and temperature during the startup was too high A new hole pattern seal sleeve was manufactured with increased clearances Theduration of the start-up was increased in order to decrease the temperature gradientAfter reassembly no high vibration appeared anymore Generally: Operation during the mechanical test (especially at trip speed) requirescareful attention if high discharge gas temperature is expecte