(i) General: Tubes that are hot or cold bent for parts of boilers,
including economizers, furnace walls, superheaters and
reheaters, shall comply with this clause and suitably
welds shall not be permitted within bends.
and departure from circularity limits shall be
demonstrated by one of the following methods.
relevant and satisfactory service experience;
a procedure test;.
By measurement of 2% of the bends, including the first
bend of each shift.
method selected shall be at the option of the
on tube bends.
Thinning on tube bends shall comply with the
At any location around the bend extrados, the reduction
in thickness (in percent) below the calculated minimum
permissible design thickness of the straight tube,
except where permitted by (b), shall not exceed:
4R + 2
is the mean radius of the bend to the centre line of the
tube (in mm).
is the ordered outside diameter of the tube (in mm).
(b) Bend thickness below the minimum value required
under (a) shall be permitted in cases where the
manufacturer can demonstrate by bursting tests carried
out on at least three bends that the strength of the
bend is not less than that of the straight tube.
(c) Where the amount of thinning at any location around
the bend extrados on cold formed bends exceeds 25% of
the actual thickness of the tube on the straight the
bends shall be suitably heat treated.
The actual thickness of the same plans as the
line of the extrados at each and of the bend.
from circularity in tube bends.
The departure from circularity at the bend apex
shall not exceed 10% for bends performed in a single
bending operation and 15% for bends which are hot
pressed after the primary, bending operation.
departure from circularity (in percent) shall be
Dmax - Dmin
is the maximum outside diameter measured in the tube
bend apex (mm),
is the minimum outside diameter measured at the
same cross section as Dmax(mm)
is the ordered outside diameter of the tube (in