| a) |
Tubes shall be connected to
the tube plates by one of the following methods:-
1) Expanding.
2) Strength welding.
3) Mechanical bolted ball joint. |
| b) |
Drift or roller expanded tubes
shall project through the neck or bearing part in the
holes by at least a quarter of an inch and shall be secured
from drawing out by being bell mouthed to the extent of
1/32” for each inch in diameter plus 2/32”. |
| c) |
Tubes may be seal welded into
fittings or headers for both boilers and super heaters
after they have been expanded and flared provided the
material in the fittings or headers does not contain carbon
in excess of 0.35 per cent. |
| d) |
In the case of drifted or roller
expanded tubes, the tube holes in the tube plates of drums,
pockets, or headers shall be formed in such a way that
the tubes can be effectively tightened in them. Where
the tube ends are not normal to the tube plate, there
shall be a neck or belt of parallel seating of at least
½ inch depth measured in a plane normal to the
axis of the tube at the holes. |
| e) |
Where tubes are strength welded
direct to the tube plates, the technique followed shall
be approved by the Inspecting Authority and all welds
shall be suitably heat treated. In the case of plates
below 22 mm thickness, the requirement of stress relieving
by heat treatment after welding of the tubes may be waived
provided the weld satisfies the requirements concerning
the maximum hardness and also the requirements concerning
the impact values of the weld metal. The welding procedure
adopted and the weld sequence selected shall also be subject
to the approval of the Inspecting Authority. This provision
is applicable to only shop welding of tubes at the Manufacturer’s
Works. |
| f) |
Tube spacers, supporting clips
and lugs may be welded to the tubes. Flash welding of
studs for supporting refractories, etc., is also permissible. |
| g) |
The tubes shall be so arranged
that they are accessible for cleaning internally and externally.
|
