Current through Register Vol. 46, No. 12, March 20, 2024
1. The
sketches in Figure 523-B illustrate acceptable preparations for joining pipe
ends by butt welding for materials having unequal wall thicknesses and/or with
unequal strengths (minimum specified yield strength).
2. The thickness of the sections to be
joined, beyond the joint design area, shall comply with the design requirements
of this Part.
3. When the minimum
specified yield strengths of the sections to be joined are unequal, the
deposited weld metal shall have mechanical properties at least equal to those
of the section having the higher strength.
4. The transition between ends of unequal
thickness may be accomplished by taper or welding as illustrated or by means of
a prefabricated transition ring.
5.
Sharp notches or grooves at the edge of the weld where it joins a slanted
surface shall be avoided.
6. For
joining unequal thicknesses of equal specified yield strengths, the rules given
herein apply, except there is no minimum angle limit to the taper.
7. THE MAXIMUM THICKNESS t
d FOR DESIGN PURPOSES SHALL NOT BE GREATER THAN 1.5t.
Internal Diameters Unequal
A. For piping to operate at hoop stresses of
less than 20 percent of specified minimum yield strength, if the nominal wall
thicknesses of the adjoining ends do not vary more than 1/8 -inch, no special
treatment is necessary provided adequate penetration and bond is accomplished
in welding. If the offset is greater than 1/8-inch the following paragraphs
will apply.
FOR STRESS LEVELS ABOVE 20 PERCENT OF THE MINIMUM SPECIFIED
YIELD STRENGTH.
B. If the
nominal wall thicknesses of the adjoining ends do not vary more than 3/32 inch,
no special treatment is necessary provided full penetration and bond is
accomplished in welding. See sketch (a).
C. Where the nominal internal offset is more
than 3/32inch and there is no access to the inside of the pipe for welding, the
transition must be made by a taper cut on the inside end of the thicker
section. See sketch (b). The taper angle shall not be steeper than 30 deg. nor
less than 14 deg.
D. Where the
nominal internal offset is more than 3/32 inch, but does not exceed 1/2 the
thinner section, and there is access to the inside of the pipe for welding, the
transition may be made with a tapered weld as shown in sketch (c). The land on
the thicker section must be equal to the offset plus the land on abutting
section.
E. Where the nominal
internal offset is more than 1/2 the thinner section, and there is access to
the inside of the pipe for welding, the transition may be made with a taper cut
on the inside end of the thicker section as shown in sketch (b), or by a
combination taper weld to 1/2 the thinner section and a taper cut from that
point as shown in sketch (d).
External Diameters Unequal
F. Where the external offset does not exceed
1/2 the thinner section, the transition may be made by welding as shown by
sketch (e), provided the angle of rise of the weld surface does not exceed 30
deg. and both bevel edges are properly fused.
G. Where there is an external offset
exceeding 1/2 the thinner section, that portion of the offset over 1/2t shall
be tapered as shown in sketch (f).
Internal and External Diameters Unequal
H. Where there is both an internal and an
external offset, the joint design shall be a combination of sketch (a to f,
i.e., Fig. g). Particular attention must be paid to proper alignment under
these conditions.
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