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Reg.254
,Reg.255,Reg.256,Reg.257

Number of joints

Where, having regard to the approved design, the dimensions are such that the shell cannot be made from a single plate, it shall be made with the minimum number of joints and the longitudinal seams in successive rings shall not fall in line except where the rings of the drum are in two halves of unequal thickness.


Reg.255

Position of the Tube holes

Tube holes in welded seams should be avoided. Where they are unavoidable they may be machined through welded seams after these seams have been radiographed, and stress relieved. The efficiency of the ligament in the direction of weld shall be multiplied by a weld factor not exceeding 0.95 except where the distance from the edge of the tube hole to the edge of the weld is greater than 13 mm (½”). The edge of the weld shall be considered to be the edge of the weld groove as machined in the plate prior to welding. 

Notwithstanding anything contained in this regulation, efficiency of the ligament in the direction of weld shall not be multiplied by a weld factor 0.95 where 100 percent radiography of  weld joint is done.



Reg.256

Circularity of drums

(a) The difference between the internal diameter of the drum measured at any cross section and the nominal internal diameter of the drum should not exceed 1 per cent of the latter.

Any departure of profile measured on the outside of the drum with a gauge of the designed form of the exterior of the drum and of length equal to a quarter of the internal diameter, shall not exceed the percentage given in table below:-

Nominal internal diameter of drum Percentage of nominal internal diameter
Up to and including 36" 0.375
Over 36" up to and including 45" 0.35
Over 45" 0.3

Flats at the welded seams shall not be permitted and any local departure from circularity shall be gradual.

(b) Tolerance (i) The deviation from circularity in any section shall, in the case of normalised drums, not exceed 2% and in case of stress relieved drum 1%.  The deviation from a straight line shall not exceed 0.3% of the cylindrical length.

(ii) In order to determine the deviation from circularity of the drums the maximum and minimum internal diameter at one cross section shall be measured.  From these measured values the percentage deviation from circularity shall be calculated according to the following formula:-

                                2(dmax dmin)

                C =   ---------------------    100                         

                                  (dmax + dmin)

where, C = percentage deviation from circularity of the drums.

                d = internal diameter at one cross section.

                In order to determine the deviation from a straight line, a stretched line should be placed longitudinally against the sides and its largest distance from the shell line concerned shall be measured.  From this distance, and from the cylindrical shell, the deviation from the straight line shall be calculated

 



Reg.257

Mechanical test and test plates for fusion welded seams

a)

Fusion Welded joints shall comply with the mechanical tests herein specified.

Not less than one set of test plates shall be provided to represent the welding of each longitudinal seam.

The test plates may be attached at each end of the longitudinal seam or the set may be located at one end only.
b) Where the drum shell is formed in two or more courses, the staggered longitudinal seam shall be regarded as a continuous longitudinal seam provided the welding be effected in one reasonably continuous operation and by the same operator or operators.
c) Where there are circumferential seams only or where the method of welding the circumferential seam differs from that employed for the longitudinal seams, the method of providing the test plates shall be decided by the Inspecting Authority.
d) The test plates shall be of a size sufficient for the preparation of the test pieces specified in Regulation 258(a) and for any repeat test pieces that may be required. The material for each set of test plates shall be cut from the respective plate or plates forming the appropriate seam, and before being cut shall be stamped by the Inspecting Officer.
e) When the analysis of the plates is approved by the Inspecting Authority and is considered sufficiently similar, the test plates may be cut from one drum shell plate only.
f) In the case of insufficient material being available on the shell plate to permit the cutting of test pieces, these shall be acceptable if they are made from another plate provided it is made from the same cast.
g) The weld groove in the test plates shall be similar to that adopted for the corresponding edges of the longitudinal seam, and the respective fusion faces shall be in continuous alignment. The test plates shall be reinforced or supported during welding in order to prevent undue warping.

The weld metal in the test plates and the seam shall be of the same grade of electrode and shall be deposited continuously at the same operation.
h) The weld in any test plate shall not be repaired unless agreed by the Inspecting Authority and the repairs shall be done in such a manner as will ensure that the repaired seam in the test plate is still representative of the material in the main seam.
i) Where it is desired to straighten test plates which have warped during welding they may be straightened at a temperature below the temperature of heat treatment of the drum to which they belong. Strengthening shall take place before final heat treatment.
j) For heat treatment, see Regulation 267.
k) If any defects in the weld metal of a test plate are revealed by radio-graphical examination, the position of these shall be clearly marked on the plate and test pieces shall be selected from such parts of the test plates as may be decided by the Inspecting Authority.
 
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