6.2.3  Methods of manufacture and construction - part 6


Shell/tube expansion

The shell and tube material thermal expansion coefficients can be markedly different, except where titanium tubes are used. Collectively, under normal operating conditions, the cumulative effects aic sufficiently large to generate theoretical stresses high enough to cause failure of the tube joint.

The differential movement between shell and tubes on a large single-pass condenser can be as high as 22 mm. A tube-to-tubeplate fixing arrangement similar to Fig 4.27 (d), but using only packed gland joints, along with tube bowing, was examined as a possible solution to this tube movement problem, but has been abandoned due to inherent unreliability. The practical solution has been to rely on the use of expansion bellows between the shell and tubeplate carrier at one end, usually of the single convolution type (Fig 4.26).

Condenser/turbine joint

A transverse underslung condenser is attached to the turbine by welding.

A typical closing weld is shown in Fig 4.28; this is a single-sided butt weld, welded from the inside, with an external backing strip. After completion, the weld is usually magnetically crack-detected for soundness.

Turbine to condenser joint (for underslug condensers)

Side-mounted condensers are bolted to the turbine exhaust flanges via flexible bellows joints.


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