ASME B16.28:1994 pdf free download – Wrought Steel Buttwelding  Short Radius Elbows and  Returns
1 General
This Standard covers ratings, overall dimensions, testing, tolerances, and markings for wrought carbon and alloy steel buttwelding short radius elbows and returns. The term  wrought  denotes fittings made of pipe, tubing, plate, or forgings.
1.2 Fabricated Fittings
Fabricated fittings employing intersection welds are not covered by this Standard. Design of such fit‑ tings is covered  in the  ASME B31, Code for Pressure Piping orthe ASME Boiler and Pressure Vessel Code. 1.3 References
1.3.1  Referenced Standards.  Standards  and spec‑ ifications adopted by reference in this Standard are shown  in  Annex  B,  which  is part of this Standard.  It is not considered practical to ideptify  the specific edi‑ tion of each standard  and specification in the indi‑ vidual references. Instead  the    specific edition reference is identified in  Annex inconformance with a prior edition of reference B.  A product  made standards  and in  all  other respects conforming to this Standard will be considered to be  in  conformance.
1.3.2  Codes and Regulations.
A fitting used un‑ der  the jurisdiction of the  ASME Boiler and Pressure Vessel  Code, the ASME Code  for Pressure Piping, or a governmental regulation  is  subject to any  limi‑ tation of that code or regulation. This includes any maximum temperature limitation or rule governing the use of a material at low temperature. 1.4 Service Conditions Criteria  for selection of fitting types and materials suitable for particular fluid service are not within the scope of this Standard.
1.5 Welding
Installation welding  requirements are outside  the scope of this Standard. Installation welding shall be done in  accordance  with the applicable piping code or regulation covering the piping system into which the fittings are installed.
2 DESIGN AND PRESSURE RATINGS
2.1 Design  of Fittings
The design of the fittings shall be established by mathematical   method  analysis contained in nation‑ ally recognized pressure vessel or piping codes or  at the manufacturer’ s option by proof testing in accord‑ ance  with Section 9 of this Standard. In order  to meet design requirements, it is  expected  that some portion of formed fittings may   have to be thicker than the pipe wall w ith which  the fitting is intended to be used.
2.2 Basis  of Ratings
The allowable pressure ratings for fittings designed in accordance with this Standard shall be as for straight seamless  pipe of equivalent size and material [nominal pipe size  (WS),  wall thickness or schedule number, and including a comparison of chemical composition and mechanical properties of the re‑ spective material specification].