Cross tubes shall be made from weldless steel pipes
or from plate or strip rolled and electric resistance
or fusion butt welded pipes by electric arc process.
The fusion welding shall conform to the requirements
of Chapter XII.
Tolerances on these pipes shall conform to the requirements
of Regulation 345.
Where welded pipes are used, the longitudinal welds
shall be so situated that they are not exposed to the
direct impact of flame.
||Cross tubes shall not exceed
12 inches internal diameter. The minimum thickness shall
be 5/16 inch.
||Where cross tubes are flanged
and riveted to the furnace the flanges shall be set to
the curvature and taper of the furnace and shall be a
good fit before riveting.
||Where welded construction is
employed the tubes shall be of sufficient length to enter
the furnace plate and the flush with the water side all
round or project not more than 5/8 inch into the water
space at any part of the circumference. Where the tubes
are fusion welded in position the firebox plates shall
be suitably chamfered and the joints shall be welded externally
and internally (see