ASME B16.25 pdf download Buttwelding Ends
This Standard covers the preparation of buttweldingends of piping components to be joined into a pipingsystem by welding. lt includes requirements for weldingbevels, for external and internal shaping of heavy-walcomponents,and for preparation of internal ends(including dimensions and tolerances). Coverageincludes preparation for joints with the following:
(a) no backing rings
(b) split or noncontinuous backing rings(c) solid or continuous backing rings(d) consumable insert rings(e) gas tungsten arc welding (GTAW) of the root passDetails of preparation for any backing ring must bespecified when ordering the component.
This Standard applies to any metallic materials forwhich a welding procedure can be satisfactorily qualified, but does not prescribe specific welding processesor procedures. Unless otherwise specified by the purchaser, it does not apply to welding ends conformingto ASME B16.5 or B16.9
1.3 Standard Units
The values stated in either metric or inch units are tobe regarded separately as standard. Within the text, theinch units are shown in parentheses. The values statedin each system are not exact equivalents; therefore, eachsystem must be used independently of the other. Combining values from the two systems may result in nonconformance with the Standard.
NPS followed by a dimensionless number, is the designation for nominal fitting size. NPS is related to thereference nominal diameter, DN, used in internationastandards. The relationship is typically as follows:
For NPS ≥ 4, the related DN is: DN p 25 NPS
1.5 Referenced Standards Standards and specifications adopted by reference in this Standard are shown in Mandatory Appendix II, which is part ofthis Standard. Itis notconsidered practi- cal to identify the specific edition of each standard and specification in the individual references; instead, the specific edition is identified in Mandatory Appendix II. An end preparation made in conformance to this Standard in all other respects will be considered to be in conformance to the Standard even though the edition reference may be changed in a revision of the Standard. 1.6 Quality Systems Nonmandatory requirements relating to the manufac- turer’s quality system program are described in Non- mandatory Appendix A.
1.7 Convention For the purpose of determining conformance with this Standard, the convention for fixing significant digits where limits, maximum or minimum values, are speci- fied shall be ‘‘rounding off’’ as defined in ASTM Practice E 29. This requires that an observed or calculated value shall be rounded off to the nearest unit in the last right- hand digit used for expressing the limit. Decimal values and tolerances do not imply a particular method ofmea- surement.
2 TRANSITION CONTOURS
Figure 1 delineates the maximum envelope in which transitions from welding bevel to the outer surface of the componentand fromthe rootface to the innersurface of the component must lie. Except as specified in Note (5) to Fig. 1 and as otherwise specified by the purchaser, the exactcontourwithinthisenvelope is the manufacturer’s option, providing it maintains the specified mini- mum wall thickness, has no slopes steeper than those indicated for the respective regions, and includes the proper surface for backing rings if specified.
3 WELDING BEVEL DESIGN
3.1 Bevels for Other Than GTAW Root Pass
(a) Components having nominal wall thicknesses of 3 mm (0.12 in.) and less shall have ends cut square or slightly chamfered.