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Reg. 575, Reg. 576, Reg. 577 a, Reg. 577 b


Flat crown plates for vertical boilers

 

i)

Flat crown plates shall be supported by the uptake and/ or bar stays .
ii) The inside radius of curvature of the flange to the shell or fire box shall be not less than four times the thickness of the plate and in no case less than 63 mm where the plate is flanged for attachment to the uptake, the inside radius of curvature of the flange shall be not less than twice the thickness of the plate and in no case less than 25 mm.
iii) The thickness of flat crown plates shall be determined in accordance with Regulation 574.



Reg. 576

Wide water spaces between and around tube nests

The thickness of plate at wide water spaces shall be calculated as per regulation 574 taking d = (A² + B²)1/2

Where,

A - is width of the wide water space between the tube nests in mm measured from centre to centre of the tubes; and
B - is pitch of the tubes in the boundary rows of the wide water space in mm.




Reg. 577 

Flat tube plates and tube nests

a) Stay tubes and plain tubes


(i) Stay tubes are tubes having a weld depth equal to the nominal tube thickness plus 3 mm as shown typically in figures XII/68A(i) to (iv). These stay tubes are not required within tube nests except when the tube nests comprise tubes which are expanded only as shown typically in figure XII/67A (iii).
(ii) If tube nests comprise plain tubes which are expanded and beaded, expanded and belled as shown typically in figure XII/67A(iv) or expanded and welded (as shown typically in Figs. XII/67A (i) and (ii) ), welded stay tubes (as shown  typically in Figs. XII/67A (i) to (iv)  shall be used in boundary rows in sufficient numbers to carry the flat plate loadings outside the tube area.
(iii) For plain tube and stay tubes exposed to flame or gas temperatures exceeding 600°C, the ends of welded tubes shall be dressed flush with the welds and the ends of the expended tubes shall be as shown in figures XII/67A(iii) and (iv). If not so exposed, the ends of welded tubes shall extended a maximum of 10 mm beyond the weld or, in the case of expanded tubes, the tubes shall project beyond the tube plate up to a maximum of 15 mm.
(iv) Each stay tube shall be designed to carry its due proportion for the load on the plates which it supports. The thickness of stay tubes welded into tube plates shall be such that the axial stress on the thinnest part of the tube does not exceed 70 N/mm².




Reg. 577 b

Parts of flat plates within tube nests


If stay tubes are used within tubes nests, the thickness of the tube plate shall be calculated in accordance with regulation 574.
 
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