Turbomachinery Laboratory, Texas A&M Engineering Experiment Station
Abstract
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
