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Reg. 151
BOILER AND SUPER-HEATER TUBES SUBJECT TO INTERNAL PRESSURE

 

Steel Tubes

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 Regulations 36 to 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 flash welded, machine forge welded, arc or gas welded. Tubes above 5” 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.  The external fin caused by welding shall be removed subject to a maximum height of 5 per cent of the tube outside diameter.  The internal fin 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 Steel 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 2¼ 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 maximum pre-heat temperature of 150°C.

for carbon steel:
(i)  a thickness of 9mm when the carbon percentage does not exceed 0.300, and

(ii) a thickness of 20mm when the carbon percentage does not exceed 0.250.".

e) When gas welding is implied the technique followed shall be approved by an Inspecting Officer.
f) For design metal temperature over 454°C (850°F) material to be used shall be in accordance with the 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.
h) All butt welds of tubes shall be tested as required hereunder:-

(i) Components greater than 178 mm (7 inch) bore.- All Welds shall be non-destructively tested by radiographic or other approved methods.

(ii) Tubes greater than 102 mm (4 inch) bore and upto and including 178 mm (7 inch) bore.- 10 per cent of the welds by each welder, selected at random with a minimum of 2 welds per welder, shall be subjected to non-destructive examination by radiographic or other approved method.

(iii) Tubes 102 mm (4 inch) bore and under.- Sample welds simulating the production welds shall be provided for mechanical testing either at a rate of 2 per cent or after each 150 welding hours with a minimum of one sample weld per welder.

 

Butt welded joints as indicated in clause (h) shall be subjected to non-destructive examination by radiographic, radioscopy or other approved methods such as ultrasonic testing, magnetic particle inspection or liquid dye penetrant inspection.  When radioscopic examination is to be performed in lieu of radiography on welded components, the following requirements shall be met, namely:-

(1)     A written procedure shall be submitted for approval to the Inspecting Authority which shall contain the following:

(i)                  material and the thickness range;

(ii)                 equipment qualifications;

(iii)               test object scan plan;

(iv)               radioscopic parameters;

(v)                image processing parameters;

(vi)               image display parameters;

(vii)             image archiving requirements;

(viii)            accept-reject criteria (Code reference);

(ix)                performance evaluation;

(x)                 Operator identification.

(2)     The system shall be aided with an image processor to enhance the quality of the radioscopic images and system performance quality shall exhibit-

(i)                  a thin section contrast sensitivity of 3%;

(ii)                 a thick section contrast sensitivity of 2%;

(iii)               a spatial resolution of 3 line pairs per mm;.

(iv)               IQI sensitivity - 2% of the joint thickness when wire IQI's are to be used, the wire diameter axis shall be oriented along the axis of the least sensitivity of the system.

(3)     Radioscopes are to be properly marked to co-relate with particular part of joint represented.

(4)     The radioscopic examination data shall be recorded and stored on videotape, magnetic disk or optical disk at the maker's plant for a sufficient period after the date of radioscopic examination as specified by the Inspecting Authority, efficient radioscopic examination record recall shall be made available at any time over the record retention period and shall be traceable to the test objects.

(5)     When repair has been performed as a result of radioscopic examination, the repaired areas shall be re-examined using the same radioscopic technique to evaluate the effectiveness of the repair.

(6)     To aid in proper interpretation of the radioscopic examination data, the details of the technique used shall accompany the data.  As a minimum, the information shall include the approved procedure requirements and system performance test data.

 


Alternatively, 5 per cent of the welds made by each welder selected at random, with a minimum of one weld per welder, shall be subjected to non-destructive examination by radiographic or other approved method. This rate may be reduced to 2 per cent by arrangement with the Inspecting Authority after initial satisfactory results have been produced.

In the event of any non-destructive test not meeting the requirements, defects in the welds represented by that test shall be rectified and the Inspecting Authority may call for an increase in the number of non-destructive tests until such time as a satisfactory standard is achieved.

 
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