The following is a summary of casing materials and their applications.
1. Cast Iron
• Limited to low pressure applications for non-flammable, non-toxic gases.
• Limited in location and size of main and sidestream connections to available
2. Cast Steel
• Quality is difficult to obtain.
• X-ray inspection requirements increase costs.
• High-rejection rate or involved repairs can extend deliveries.
3. Fabricated Steel
• Used for both horizontally- and vertically-split casings.
• Improved quality control possible.
• Delays associated with rejection or repair of castings are avoided.
• Variable stage spacing provides minimum bearing span for required stages.)
• Main and sidestream nozzle size and location are not limited by pattern availability.
4. Forged Steel
• Used for small vertically-split casing sizes where application involves very high pressures.
All centrifugal compressor casings used to be cast. But, due to the problems associated with quality control on large castings, coupled with improved fabrication techniques and costs, many manufacturers converted to fabricated steel casings, especially on the larger frame sizes.