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.

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 ⅛ -inch, no special treatment is necessary provided adequate penetration and bond is accomplished in welding. If the offset is greater than ⅛-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 ½ 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 ½ 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 ½ the thinner section and a taper cut from that point as shown in sketch (d).

F. Where the external offset does not exceed ½ 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 ½ the thinner section, that portion of the offset over ½t shall be tapered as shown in sketch (f).

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.