STRUCTURAL ERECTION OF STEAM GENERATOR PART-IV.

Structural erection of steam Generator /boiler can be divided into few parts according to the importance .

a. Preparation of soil inside the cavity for heavy duty crane movement  in spite of columns located 

inside the cavity. 

b. Secondary grouting of the columns  by  ready mix concrete.

c.  Procedure of torque tightening of HSFG bolts .

d. Most important item is fabrication and erection of Ceiling Girders . This is heaviest structural items

 to be lifted at site. 

e. Structural items like beam ,bracing , welded beams ,rolled beams , angles ,channel , fabricated piece

etc are erected as per drawing as routine erection but a planning needs to be done before hand so that

clear passage to be kept at ground level so that crane can move inside and also passage to be made 

for pressure parts material movement. It may require a few bracing to be kept on hold for erection.

The above picture shows a heavy duty crane is standing on platform . Platforms are made to size by 

20 mm steel plates and ISMC 100/ISMC 150 channel. These platforms made such a way that crawler

of the crane can stand on it. Platforms can be easily removed from one place to another while the 

crane is on move. In some place 12" square and 10' -12' long  wooden logs are used instead of steel 

platform. However  arranging wooden logs  is very difficult now a days therefore every body tries to

make steel platforms. The soil need to be compacted by running roller if required boulder pitching

has to be carried out. Laying of platform should be done such a way that there should not be any

load on the foundation columns located inside the cavity. This can be understood if some one can

looked into the boiler plan given on earlier submission. Any heavy duty crane of 600 MT or 1200 MT

needs to stand  firmly on platform within a limit of undulation . Crane manufacturer set half a degree

is the max limit. A crane sizing ( capacity) depends on lifting of ceiling girder ( heaviest one ) to 

required height. In our 660 MW we choose 600 MT Manitowac crane with luffing jib at 67 M and 

jib can lift the heaviest girder. This was done to keep in mind the erection of welded beams , rolled 

beams and roof structure including the silencers. Our erection method i.e erecting boiler structure

from the cavity does not suit the heavy lift crane with super lift arrangement as crane will not have

radius to move. Above picture shows the crane platform from other angle.

we will discuss secondary grouting of columns and HSFG bolting at the end.

We will now discuss about the ceiling Girder fabrication and erection.

The limits set out for ceiling Girder pre-fabrication is given below.

- Root gap at the erection joint of the ceiling Girder. Flange 4 mm to 6 mm , web 6 to 10 mm.

- Camber and sweep of individual ceiling girder 1 mm/ M , max. 15 mm

- Assembled ceiling girders for sweep and camber  1 mm / M max 15 mm.

- Position of Bottom bolt hole with reference to centre of the ceiling girder  + /- 3 mm

- Spacing between adjacent ceiling girder +/- 5 mm ( taken during Girder alignment)

- Diagonal difference between to adjacent girders is  25 mm Max .

-ceiling girders centre line variation w.r.t. Boiler axis  12 mm Max.

continued to part-v

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