Reg. 542, Reg. 543, Reg. 544
For the purpose of relieving internal stress all plates
which have been dished, flanged or locally heated shall
afterwards be, annealed unless during the last stage
of manufacture they have been uniformly heated throughout.
|Except where the design incorporates
flat tube plates in the shell, each ring shall be formed
from not more than two plates and bent to cylindrical
form to the extreme ends of the plate. The bending shall
be done entirely by machine. Local heating or hammering
shall not be used.
The longitudinal seam or seams may be placed in any suitable
position but the seams in successive rings shall not fall
In the case of brick set boilers the seam or seams shall
be kept as far as practicable clear of the brickwork.
The difference between the maximum and minimum internal
diameters of the shell measured at any one cross section
shall not exceed 1 per cent of the nominal internal
The profile as measured on the outside of the boiler
by means of a gauge of the designed form of the exterior
of the boiler, having a length equal to one quarter
of the internal diameter, shall not depart from the
designed form by more than the percentage given in Table
Maximum percentage departure from designed form
of welded boilers
|Nominal internal diameter of boiler
||Maximum departure from designed form
|Up to and including 36
|Over 36, up to and including 45
There shall be no flats at the welded seams and any local
departure from circularity shall be gradual.