Reg. 578, Reg. 579 A, Reg. 579
Manhole openings in flat plates
Where manholes are located in flat plates, the opening
shall be suitably compensated.
Compensation shall be obtained by flanging the edge
of the opening, or by providing a fabricating ring
(see Figs. XII/52,
The manhole in the lower portion of the flat front end
plates shall be fitted with a flanged strengthening
ring, the thickness of the flat portion of which shall
be not less (1.5T +1/8 inch)
Where T=the thickness of the end plate in inches, and
in boilers of 7 feet and 6 inches diameter and over
the manhole frame shall be fitted with a peak to reinforce
the portion of the end plate between and below the furnaces
and this peak shall be securely welded there to.
In all cases the depth of the flanging or ring shall
not be less than that determined by Equation XII/6.
NOTE:-Where the manhole is located in or between tube
nests in Multi-tubular boilers or below the furnaces
of other Boilers the stay tubes in the boundary rows,
or the gusset stays, as applicable, shall be arranged
as closely as practicable to the manhole.
Plain tubes may be welded at both ends, welded at the
inlet end and expanded at the outlet end, or expanded
at both ends.
Where the tubes are expanded only, the process shall
be carried out with expanders having parallel rollers,
and the expanded portion of the tube shall be parallel
through the full thickness of the tube plate. In addition
to expanding tubes may be bell-mouthed or beaded at
the inlet end.
Where the tube is welded to the tube plate, the tube
should be lightly expanded to grip the tube hole before
(b) The thickness of
tubes under external pressure shall be calculated as under:-
t = minimum thickness of tube in mm.
WP' =External working pressure in kg/cm²(g)
D = Outside tube diameter in millimetres
C = Corrosion allowance to be taken as 0.75 millimetre
Stainless steel C=0.
Higher value may be adopted if desired by user;
F = allowable stress as per regulation