maximum permissible stress for drum shells and headers
shall be taken as available in governing Boiler codes of
the country of the material to which it belongs.
In case of non-availability of the value, the
following procedure for evaluating shall be adopted.
For temperatures at or below 454o C,
the smaller of the two values:-
For temperatures above 454o C, the
least of the following three values:-
t = Working
R = Minimum
specified tensile strength of the steel at room
E = Minimum
specified Yield point at room temperature
Et = Yield Point
(0.2% proof stress) at the temperature 't'.
Sc = The average stress to produce an elongation
of 1% (creep) in 100,000 hours at temperature 't'.
average stress to produce rupture in 100,000 hours at
the temperature 't' and in no case more than 1.33 times
the lowest stress to produce rupture at the temperature.
case Sc values are not available in Material Standard
and such materials are known to have been used in
boilers in India or abroad, then for such materials the
allowable stress may be taken as the lower of
fusion welded drums, when the wall thickness exceed 60mm
(2-3/8"), a deduction of 1 per cent in the value of
"f" so determined shall be made for each
increase of 5mm (3/16") in the thickness.
Such deduction need not be made provided the
minimum specified values of R and E at any part of the
section of the steel plate used in the manufacture of
the Boiler drum are guaranteed by a "Well known
Steel Maker" or certified by an Inspecting
working metal temperature shall be taken as:-
For saturated steam, water and mud drums, the
saturation temperature corresponding to the pressure WP
For superheated steam the designed maximum steam
temperature for that drum plus 50oF.
the drums are adequately protected from the gases of
combustion or swept by such gasses in the third or
subsequent pass of a boiler, the working metal
temperature shall be taken as the saturation or designed
maximum steam temperature as defined above, whichever
covering of refractory or insulating material which may
be liable to become dislodged shall not be deemed
Where steels are for service at temperatures in excess
of 370oC (700o F) it shall be so
stated as the silicon content shall be 0.10 per cent
minimum or alternatively the material must pass the
"Proof Test for Creep Quality of Carbon Steel Plate
of Boiler Plate Quality" as in the Appendix D