CROSSOVER BELLOWS

Crossover bellows are another example of the specialised steam pipe expansion joints. These are installed at steam turbines where high-pressure/ high- temperature steam is transferred to one or more low pressure turbines.
This system increases efficiency by taking the remaining energy in the steam and pass it through the high-pressure part of the system, thus using it to drive the machines at the low pressure section. The special steam pipe expansion joints are installed in the pipe system connecting the turbines where they absorb the thermal growth of the pipe system together with any movement of the turbine nozzles occurring under load conditions.

Crossover bellows are available in all sizes, all materials and all types.

Crossover bellows are available in all types to suit the turbine and are typically bespoke items. The types can be:

• Pressure balanced
• A hooded design
• Tied unit (gimbals, hinged or tie rods)
• Combination of angular and lateral expansion joints

Crossover piping bellows are invariably custom-designed to suit the arrangement of the turbines and interconnecting pipe system. Depending on the pipe arrangement, the expansion joint type may be an articulated design, corner relief design, hooded design or a combination of angular and lateral expansion joints. A very important part of the design process is that the expansion joint designer ensures that the forces and movements resulting from thermal and mechanical movement are within the acceptable limits specified by the turbine manufacturer. The turbine exhaust nozzles are normally the most sensitive to mechanical loads.

What are the advantages of using Crossover bellows?

The introduction of crossover steam piping bellows enables the thermal and mechanical movements to take place without imposing unacceptable loads on the turbine casing.
A pressure-balanced arrangement is invariably used to eliminate any pressure forces from the bellows in the expansion joint, and it would be impractical to provide separate fix points on the pipe system to contain these loads. Good expansion joint design results in minimal loadings to the turbine casings as to improve the efficiency and reliability of the turbines that are one of the most critical parts of a power plant.

Crossover bellows are mainly used on steam turbines (exhaust, condensers and crossover piping).