ABSTRACT
Fabricated parts of the boiler can be divided broadly into the following categories:
1. Unheated pressure parts (PPs) (coded parts kept mostly outside the gas pass) 2. Draft plant items (mainly sheet metal work) 3. Structures (mainly rolled and fabricated steel work)
These parts do not participate in heat transfer, other than in the gas-swept portions of the drums in the bidrum bank. Nor are they fi nished auxiliary items that contribute to the performance of the boiler. The fabricated items are mostly static and perform the following background functions:
• Support the boiler, its various components, and machinery • Transport the fl uids, gas, and air (in fl ues and ducts), and water or steam (integral
piping)
Unheated PPs are pressure-containing pipes and drums outside the gas passes:
1. Steam drums 2. Risers and downcomers (unheated) 3. Integral piping
Steam drums and risers and downcomers are parts of the boiler circulation system and connected to the evaporator surfaces. Integral piping comprises drain, soot blower (SB), blowdown, and all interconnecting piping for superheater (SH) and reheater (RH) to complete the circuits. Other than the drums, all the unheated PPs are made of pipe work. There is no heat transfer and no close bending requirement as in tube banks. Also, the range of sizes is higher, from 25 mm nominal bore (NB) to 457 mm OD. The tubulars are pipes as opposed to tubes used inside the boiler for tube banks, coil work, and panels.
