What type of fitting is used to connect the branch pipes at the upstream end
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Hello, dear marine engineers. When connecting a branch pipe of different diameter to a main pipe, how do we determine whether to use an elbow with different diameters or simply weld a hole directly? If welding a hole is used, is it necessary to use a reinforcement plate? If so, what thickness should the reinforcement plate have? Are there such standards and specifications? I hope experts can reply. Thank you!
The reduction sizes used for reducing tees and pipe sockets are different; check ASME B16.11 and MSS-SP-97
Refer to clause 5.1.7 of GB/T20801.3: 5.1.7 Branch connections and their fittings. 5.1.7.1 Branch connections include two forms: the direct welding of a branch to the main pipe, and the connection of the branch to the main pipe through fitting components. Such fitting components include branch supports, half-elbows, tees, etc. The branch connection fittings for GC1 class pipelines shall comply with the provisions of 5.1.7.2. The welded connection between the branch pipe and the main pipe shall comply with the provisions of 5.1.7.3. 5.1.7.2 Fittings for branch connections on GC1-class pipelines a) Fittings for branch connections used on GC1-class pipelines shall be integrally reinforced branch connection fittings or tees ； b) The nominal diameter of socket or threaded branch fittings and half-fittings shall not exceed DN80 ； c) The selection of threaded pipe fittings shall comply with the relevant provisions of 5.2.5. 5.1.7.3 Welded connection of branch pipes to main pipes a) The pressure design shall be carried out in accordance with the provisions of 6.7, and the welding shall comply with the requirements of 5.2.2.1. b) For use in conditions of severe cycling, in addition to meeting the requirements of 5.1.7.3 a), the structure shown in Figures 10 b), 10 d), and 10 f) of GB/T 20801.4–2006 shall also be adopted. c) Welded connections between branch pipes and main pipes should not be used in the following situations: 1) When the size of the branch pipe is similar to that of the main pipe ； 2) The connection area is subject to cyclic stresses caused by loads such as vibration, pulsation, and temperature cycling. d) When there is a significant difference in size between the branch pipe and the main pipe, the branch pipe should have sufficient flexibility to compensate for the thermal expansion of the main pipe and other displacements (see 7.3.3). In summary, for GC1 pipes, tees or fittings with integral reinforcement are the most suitable options; open welding or open reinforcement is not appropriate. For pipes that are not of GC1 type and have a diameter of ≤DN40, half-elbow joints or socket-welded branch fittings are generally used. For pipes with large branch diameters and low pressure, open welding can be employed. It is necessary to conduct calculations to determine whether reinforcement is required; if reinforcement is needed, it should be carried out using the equal-area reinforcement method specified in GB/T20801. If you do not want to perform the calculations, you can choose from those elbow fittings specified in the standards – any elbow fitting listed in GB/T12459 or GB/T13401 will work. If there is a large difference between the diameter of the main pipe and that of the branch pipes, and no appropriate elbow fitting is available in the standards, then a butt-welded branch fitting can be used.
What is your field of specialization? If it’s design, then refer to the regulations regarding pipe material selection; these guidelines specify the methods for connecting main pipes and branch pipes, including the use of tees, pipe supports, and half-pipe fittings. If it’s for construction, you can ask the designer.
Please study Article 5.1.7 of GB/T20801.3 in detail
Under normal circumstances, the design institute should include a branch pipe connection table in the pipeline design documents, providing detailed specifications for different main and branch pipe sizes, as well as for various pipeline grades.
It depends on the actual construction conditions on site; the standards are fixed, but flexibility is needed to adapt to the specific circumstances
Well, I learned how to connect pipe branches!
Check the GB/T12459 standard to see if it specifies dimensions for reducer tees; if not, half-pipe joints or branch fittings can be considered based on the pressure requirements. Refer to standards GB/T14383 and GB/T19326 as well. For perforated welds, refer to GB/T20801