6.2.3 Methods of manufacture and construction - part 3
The condenser shell forms the boundary of the steam envelope. The structure comprises a floor, two side-walls, and end plates with provision for expansion and location of tubeplates. The build-up of a condenser shell varies between manufacturers.
British experience has shown, however, that the various manufacturing practices produce end products which are comparable in quality, cost and construction time. The sections making up the condenser shell are invariably built up from steel plates welded together, the only exception to this being the tubeplate attachment, which is arranged for bolting or studding to shell and flanges. The shell is sometimes stiffened for vacuum and structural loading by separate stiffening members, but more generally the necessary support is provided by welding the intermediate tube support plates direct to the shell. After welding, all shell envelope and major structural welds are crack-detected, using magnetic particle non-destructive testing or an equivalent check.
The design and layout of tubenests is extensively covered in Section 5 of this chapter, which emphasises how the disposition of the tubes within the shell is the heart of any condenser design. The present tubenest arrangement consists of an upper and lower tubenest, each taking the form of a 'folded band' of tubes (Fig 4.20 (b)). This design draws not only on the experience gained during many years of manufacture of condensers, but also on knowledge derived from model tests and from tests on other large condensers in Britain, and overseas.
Clean conditions are established within the condenser shell prior to commencement of tubing. Tubing is usually started at the bottom rows, working progressively upwards. When the bottom rows are complete, it is possible to remove personnel as these rows then act as supporting guides when inserting subsequent rows of tubes. Guide bullets in the leading end of the tube greatly assist the tubing operation.