2. Insufficient mass and.or rigidity
Improper installation is not a design weakness. This defect can be corrected rather easily in the field at any time after installation. Insufficient mass or rigidity is a design weakness brought about by the complexity of the origin of vibration in high-speed rotating machinery and its sensitivityof vibration. Nevertheless， mass and rigidity can be increased in thefield， but it is more of a task to do so than the mere correcting of installation defects.
Installation .efects
A typical compressor train containing a turbine and two compressor stages are shown in Figure 21-14. The I-beams on the platform are grouted to the concrete structure. When proper grouting techniques are carried outduring the original installation， the grout should contact the entire lower surfaces of all longitudinal and transverse I-beams.
Cement-based grouts will not bond well to the platform load-bearingsurfaces. Over a period oftime， lubricating oils will severely degrade both cement groups and concrete. This problem is further aggravated because
Figure 21-14. . typical compressor train containing a turbine and t.o compressor stages.
most platforms are not designed with oil drains. On several occasions， as much as 6-8 inches of oil has been found trapped within the platform cavities. This condition not only provides head-pressure for an increasedrate of oil penetration， but also creates a severe fire hazard.
All platforms， regardless of the type of grout to beused， should be designed with oil drains. Epoxy grouts are recommended on platform installations because they provide an excellent oil barrier for the concrete below. Cement grouts should be used only for temporary installations.
When differences in vibration amplitudes can be detected between thelower flange of the platform beams and the concrete structure， the decision to bond the entire lower surfaces of the platform to the concrete structure should be made. Bonding can be accomplished using a technique known aspressure-grouting. With this technique， holes are drilled through the lower flange at locations near the web on centers of approximately 18 inches. Theseholes are then tapped， and ordinary grease fittings are installed. Pressure-grouting can then be carried out with either automatic injection equipment or with conventional grease guns.
Some manufacturers recommend that their platforms be installed onrails or sole plates， which have been grouted to the concrete foundation.Occasionally， the installation will be either poorly designed or the contractor will fail to clean the plates before grouting. Loss of adhesion may result in excessive vibration or movement of the plate in the grout. When this pro-blem occurs， pressure-grouting can be accomplished with a relatively high degree of success if proper techniques are used. The following are some main points to consider when designing and grouting a sole plate:
1. Check to see that the block between the equipment base and the sole plate is adequate to transmit the load.
2. Corners on the edges of the sole plate should have at least a two-inch radius to prevent the creation of stress risers and subsequent cracking of the corners.
3. There should be a sufficient amount of aggregate in the epoxy mix-ture. Insufficient quantities of aggregate will lead to a layer of unfilled epoxy on the surface of the mortar. The linear coefficient of thermal expansion of the unfilled epoxy can be expected to be on the order of magnitude of 6-8 . 10ι5 inches per inch of thickness per 0F. The linear coefficient of thermal expansion for the epoxy mortar below can be expected to be on the order of magnitude of 2 . 10ι5 inches per inch of thickness per 0F. This difference in thermal expansionrates will encourage crack propagation， particularly on cooling when the system is subjected to cyclic temperatures such as between day and night. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 3(93)
