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Reg. 337
BOILER AND SUPER HEATER TUBES, HEADERS AND OTHER PRESSURE PARTS TUBES


Material and Construction

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.
 
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