Half Coupling in lieu of Weldolet-Code Issues ASME B31,3

[stanier]

On low pressure SS piping the use of a half coupling welded onto the pipe was a cost effective solution to the use of a weldolet. The half coupling weld preparation was a bevel at 45 degrees. The fitting sat on the header rather than in a hole in the header.

What are the code issues with the use of such a fitting. Are there pressure limitations? I need to investigate the fatigue issues.

I apologise beforehand for not delving into the Code myself. I am out of office and dont a copy to hand right now.



Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[BigInch]

Diameters and thicknesses? Is there any reinforcement?
Well, here's the code for a branch, minus the formulas and diagrams.

304.3 Branch Connections
304.3.1 General
(a) Except as provided in (b) below, the requirements
in paras. 304.3.2 through 304.3.4 are applicable to
branch connections made in accordance with the following
methods:
(1) fittings (tees, extruded outlets, branch outlet
fittings per MSS SP-97, laterals, crosses);
(2) unlisted cast or forged branch connection fittings
(see para. 300.2), and couplings not over DN 80
(NPS 3), attached to the run pipe by welding;
(3) welding the branch pipe directly to the run
pipe, with or without added reinforcement, as covered
in para. 328.5.4.
(b) The rules in paras. 304.3.2 through 304.3.4 are
minimum requirements, valid only for branch connections
in which (using the nomenclature of Fig. 304.3.3):
(1) the run pipe diameter-to-thickness ratio (Dh /
Th) is less than 100 and the branch-to-run diameter
ratio (Db/Dh) is not greater than 1.0;
(2) for run pipe with (Dh /Th) ? 100, the branch
diameter Db is less than one-half the run diameter Dh;
(3) angle  is at least 45 deg;
(4) the axis of the branch intersects the axis of
the run.
(c) Where the provisions of (a) and (b) above are
not met, pressure design shall be qualified as required
by para. 304.7.2.

(d) Other design considerations relating to branch
connections are stated in para. 304.3.5.
304.3.2 Strength of Branch Connections. A pipe
having a branch connection is weakened by the opening
that must be made in it and, unless the wall thickness
of the pipe is sufficiently in excess of that required to
sustain the pressure, it is necessary to provide added
reinforcement. The amount of reinforcement required
to sustain the pressure shall be determined in accordance
with para. 304.3.3 or 304.3.4. There are, however,
certain branch connections which have adequate pressure
strength or reinforcement as constructed. It may
be assumed without calculation that a branch connection
has adequate strength to sustain the internal and external
pressure which will be applied to it if:
(a) the branch connection utilizes a listed fitting in
accordance with para. 303;
(b) the branch connection is made by welding a
threaded or socket welding coupling or half coupling
directly to the run in accordance with para. 328.5.4,
provided the size of the branch does not exceed DN
50 (NPS 2) nor one-fourth the nominal size of the
run. The minimum wall thickness of the coupling
anywhere in the reinforcement zone (if threads are in
the zone, wall thickness is measured from root of
thread to minimum outside diameter) shall be not less
than that of the unthreaded branch pipe. In no case
shall a coupling or half coupling have a rating less
than Class 2000 per ASME B16.11.
(c) the branch connection utilizes an unlisted branch
connection fitting (see para. 300.2), provided the fitting
is made from materials listed in Table A-1 and provided
that the branch connection is qualified as required by
para. 304.7.2.

(c) the branch connection utilizes an unlisted branch
connection fitting (see para. 300.2), provided the fitting
is made from materials listed in Table A-1 and provided
that the branch connection is qualified as required by
para. 304.7.2.

304.3.3 Reinforcement of Welded Branch Connections.
Added reinforcement is required to meet the
criteria in paras. 304.3.3(b) and (c) when it is not
inherent in the components of the branch connection.
Sample problems illustrating the calculations for branch
reinforcement are shown in Appendix H.

304.3.5 Additional Design Considerations. The requirements
of paras. 304.3.1 through 304.3.4 are intended
to ensure satisfactory performance of a branch
connection subject only to pressure. The designer shall
also consider the following.
(a) In addition to pressure loadings, external forces
and movements are applied to a branch connection by
thermal expansion and contraction, dead and live loads,
and movement of piping terminals and supports. Special
consideration shall be given to the design of a branch
connection to withstand these forces and movements.
(b) Branch connections made by welding the branch
pipe directly to the run pipe should be avoided under
the following circumstances:
(1) when branch size approaches run size, particularly
if pipe formed by more than 1.5% cold expansion,
or expanded pipe of a material subject to work hardening,
is used as the run pipe;
(2) where repetitive stresses may be imposed on
the connection by vibration, pulsating pressure, temperature
cycling, etc.
In such cases, it is recommended that the design be
conservative and that consideration be given to the
use of tee fittings or complete encirclement types of
reinforcement.
(c) Adequate flexibility shall be provided in a small
line which branches from a large run, to accommodate
thermal expansion and other movements of the larger
line (see para. 319.6).
(d) If ribs, gussets, or clamps are used to stiffen
the branch connection, their areas cannot be counted
as contributing to the reinforcement area determined
in para. 304.3.3(c) or 304.3.4(f). However, ribs or
gussets may be used for pressure-strengthening a branch
connection in lieu of reinforcement covered in paras.
304.3.3 and 304.3.4 if the design is qualified as required
by para. 304.7.2.
(e) For branch connections which do not meet the
requirements of para. 304.3.1(b), integral reinforcement,
complete encirclement reinforcement, or other means
of reinforcement should be considered.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com