| a) |
All tubes which are subject
to internal pressure of water or steam shall be cold drawn
or hot finished seamless or electric-resistance welded
in accordance with Regulation
36 & 63, Except
as provided for in clause (b) below they shall be without
joint. |
| b) |
Tubes having an external diameter
not exceeding 5 inches may be jointed and such joints
may be flashed welded, machine forge welded arc or gas
welded. Tubes above 5 inches diameter may also be welded
provided they are located outside the furnace. Such welds
must conform to the requirements of Chapter
VIII. |
| c) |
Flash welding shall be undertaken
on a welding machine of a type approved by the Inspecting
Officer and the external fin caused by welding shall be
completely removed. The internal fin caused by welding
shall also be removed subject to a maximum height of 20
per cent of the wall thickness of the tube. |
| d) |
Arc welded butt joints shall
be made by the metallic shielded arc process and post
weld heat treated effectively except in the following
cases:
For alloy steel:
(i) in case of 0.5 Molybdenum steels if thickness does
not exceed 13 mm and outside diameter does not exceed
127 mm.
(ii) In case of 1 Chromium ½ Molybdenum steel if
thickness does not exceed 13 mm and outside diameter does
not exceed 127 mm and pre-heated to 125°C.
(iii) In case of 2-1/4 Chromium 1 Molybdenum steel, post
weld heat treatment is not necessary under the following
conditions:
(1) a maximum specified chromium content of 3.0%.
(2) a maximum nominal outside diameter of 102 mm.
(3) a maximum thickness of 8 mm.
(4) a maximum specified Carbon content of 0.15%.
(5) a minimum pre-heat temperature of 150°C.
For carbon
steel:
(i) a maximum carbon percentage of 0.30.
(ii) a maximum thickness of 9 mm.
|
| e) |
When gas welding is implied
the technique followed shall be approved by an Inspecting
Officer and all welds shall be suitably heat treated. |
| f) |
For design metal temperature
over 454°C (850°F) material to be used shall be
in accordance with Regulations
48, 53 and 56A. |
| g) |
The technique employed in all
field welding of tubes shall be subject to the approval
of the Chief Inspector of Boilers.
Where, however, material used is in conformity with the
Code of the country of manufacture and it is covered by
these Regulations, the permissible stress figures specified
in the Code at different temperatures may be accepted
in lieu of figures computed from the data required to
the furnished under Regulations
338 and 340
in any of the following cases:-
(i) Where a certificate is furnished from the Inspecting
Authority to the effect that the steel complies with requirements
of the grade steel (to be specified) and that the permissible
stress for the working conditions as allowed for in the
code of the country of manufacture falls within the limits
permissible under the Regulations.
(ii) Where the basis upon which these stresses have been
arrived at is made available and such basis is not found
to be such as to give rise to stresses higher than those
permissible under the Regulation. |
