||Sections of internal
flues shall each be made from one plate which shall be
bent while cold to circular form. The longitudinal seam
shall be forge lapwelded, or fusion butt-welded by the
metal arc process.
||The maximum permissible
variation in diameter of any cross section shall not exceed
¼ inch or half the thickness of the plate, whichever
shall be placed at the lower part of the furnace and shall
break joint in successive sections at least by 150 mm.
||Where the flue sections
are flanged for circumferential joints the flanging shall
be carried out at one heat by suitable machinery.
||Edges of all flue
flanges shall be machined or flame-cut by machine (See Regulation
seams shall be arranged so that they do not fall in line
with those of the adjacent flue or with circumferential
seams of the shell.
||The minimum mean internal
diameter of furnaces shall not be less than those given
in Figure XII/20A
depending on the not heat input.
||Where furnace flue
is made up of plain or corrugated sections or both, they
may be connected to each other by fusion butt-welded circumferential
||Plain furnaces shall
not exceed 3m in length except in the case of reverse
flame boilers, which are considered to be inherently
flexible or as provided in clause (ii). In all other
cases flexibility shall be provided in the furnace
by means of corrugations or bowling hoops or
of a minimum of 150 mm I the diameter of the furnace.
See figures XII/20B,20C,20D,20E
& 20 F.
If corrugations are used to provide flexibility;
at least one-third of the furnace length shall be
Breathing spaces as per sub-regulation (i) of regulation
590 shall be provided for boilers made as per
||Notwithstanding the provisions
of clause (I), plain furnaces longer than 3 m are
allowed to be used in a boiler when the length between
boiler and plates does not exceed 6.5 metres provided
that breathing spaces used in this case are in accordance
with sub-regulation (ii) of regulation
||Where a complete
flue is constructed of short plain sections, the ends
of each adjoining section shall either be swaged out to
a radius to provide an adequate point of support and longitudinal
flexibility and butt-welded together or be butt-welded
to each side of a bowling hoop. The dimentions shall comply
with Figures XII/23,
by heat-treatment shall be carried out when the construction
of a flue involves the use of a circumferential weld,
such stress relieving being carried out on the completion
of all welding in accordance with regulation
||The forms of the
connections to end plates shall be as shown in Figures
XII/13, XII/14, XII/15 and XII/16 and XII/16A
to the approval of the Inspecting Authority, be in any
other form of welding groove.