Wall thickness of Pipe fittings

Not necessarily, from ASME B16.9:

---------------------------------

2.2 Design of Fittings
The design of fittings shall be established by mathe-
matical analyses (e.g.,ASME B16.49 for bends) contained
in nationally recognized pressure vessel or piping codes,
or at the manufacturer's option by proof testing in accor-
dance with section 9 of this Standard. In order to meet
design or manufacturing requirements, it is expected
that some portion of formed fittings may have to be
thicker than the pipe wall with which the fitting is
intended to be used. The mathematical analyses, if used,
may take into account such thicker sections. Records of
mathematical analysis and/or successful proof test data
shall be available at the manufacturer's facility for

inspection by the purchaser.

-----------------------------------------------

For example standard weldend 'T's (size by size) - there needs to be reinforcing in the sidewall - this is most evident from looking at different T's from different manufactureres, some are bulbous/spherical, while others are straighter.

Also the thickness variation requirements of the intrados and extrados of elbows/bends.