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Weldolet – Integral reinforced forged branch outlets

Weldolet fittings – the Branch Connection Fittings are also named as Outlet fittings. Outlets are a family of forged products used to make 90 degree or 45 degrees integrally reinforced branch connections from a header pipe or run pipe to an outlet pipe or branch pipe. 

When stress concentrations and cyclic loads are a concern, detailed analysis is required. With a complete FEA analysis, the required strength for any demanding use or application can be determined.

The integrally reinforced branch outlet fittings and the deposited weld metal used to attach the fittings to run pipes contain all the reinforcement required by the applicable pressure or piping code.
The adequacy of the design of branch connection fittings may by established by mathematical analysis contained in the pressure vessel or piping code or by proof testing in acc. to the applicable code.

Weldolets are typically used in high-pressure and high-temperature applications where a strong and reliable connection is required. Weldolets are also used in applications where a smooth transition between the run pipe and the branch pipe is important, such as in fluid flow applications.

Integral reinforced forged branch outlets are preferably used in industrial pipelines and pressure vessels instead of welded T-pieces, branches with reinforcement plates, branches with reinforcement saddles and unreinforced branches.

Standard MSS SP-97

MSS SP-97 is the generally standard for design, size and class of integrally reinforced forged branch outlets and referred in a piping codes. The dimensions are provided in two unit systems: US customary unit or SI metric unit. A table contain the correlation of fittings class with Schedule number or run/branch wall designation of pipe for calculation of ratings

Table: Correlation of fittings class with Schedule number or run/branch wall designation of pipe for calculation of ratings

Class of fittingTypeBranch size
Branch size
Run Pipe Wall for Rating Basis (a)Branch Pipe Wall for Rating Basis (a)
StandardButwelding1/8 – 246 – 600StandardStandard
Extra StrongButwelding1/8 – 246 – 600Extra StrongExtra Strong
Schedule 160Butwelding1/2 – 615 – 150Schedule 160Schedule 160
Double Extra StrongButwelding1/2 – 615 – 150Double Extra StrongDouble Extra Strong
3000Threaded1/8 – 46 – 100Extra StrongExtra Strong
6000Threaded1/8 – 26 – 50Schedule 160Schedule 160
9000Threaded1/8 – 26 – 50Double Extra StrongDouble Extra Strong
3000Socket Welded1/8 – 46 – 100Extra StrongExtra Strong
6000Socket Welded1/8 – 26 – 50Schedule 160Schedule 160
9000Socket Welded1/2 – 215 – 50Double Extra StrongDouble Extra Strong
(a) The use of run and branch pipe wall thickness either thinner and thicker than as show in this table is to be agree between the manufacturer and the purchaser.
Typical Weldolet

The forged branch outlets can be furnished in butt welding, socket welding, and threaded types which are known as Weldolet (weld outlet), Thredolet (thread outlet), and Sockolet (socket outlet), respectively.

Types of Weldolet® – Integral reinforced forged branch outlets fittings

Type1Designation 1Designation 2Size range
Weldolet®Weld outletThe weldolet is ideal for replacing a tee on 90-degree branches with a reinforced connection that protects the branch pipe by reducing stress concentration due to its shape and size.Weldolet is the type of fitting used to create a branch with the smaller size of main pipe1/8 NPS – 24 NPS
Thredolet®Thread outletNormally, Thread Branch Outlet Fittings are used for NPS under 2″.1/8 NPS – 6 NPS
Sockolet®Socket outletSocket Weld Outlet has the same basic design as a welding outlet and Threaded Outlet where the major difference is that the branch pipe is connected to the run pipe, via the fitting, with a socket weld connection1/8 NPS – 6 NPS
Nipolet®Nip outletsNipple Outlet is mostly used for valve installation.Nipple Outlets are manufactured in lengths ranging from 3.1/2 inches to 6.1/2 inches and for Sch 160, XS, and XXS schedules1/8 NPS – 6 NPS
Elbolet®Elbow outletElbow Outlet is used to provide branch connections on 90 or 180 degrees short radius elbows (seldom used) or long radius elbows (most common). Most used for thermowell and instrumentation connectionsElbow Outlets are available with socket weld/threaded connections or with butt weld connections in class 3000 or class 6000.1/8 NPS – 6 NPS
Latrolet®Lateral OutletThe lateral outlet are also known as 45° (or 60°) branch outlets which can be furnished with butt welding end, threaded end and socket welding endThe fittings designed to connect the large bore headers with angled branch pipe mostly at 45° or 60°1/8 NPS – 6 NPS
1 Trademark of Bonney Forge

EN 13480 series application for industrial piping

The use of integral reinforced forged branch outlets for industrial pipelines in accordance with the EN 13480 series is generally possible. EN 13480-3 contains calculation rules for this, if certain conditions are met, such as those contained in EN 13480-3 Table H.3.

There is no harmonised standard for integral reinforced forged branch outlets according to the PED. The manufacturer must prove in each individual case that the intended outlet, e.g. sizing according to MSS SP-97, meets the requirements of the PED or EN 13480-3,

In order to be used within the established ratings, the forged branch outlets shall be design proof tested in acc. to the EN 13480 Series.

Piping Codes application in according to ASME

The integrally reinforced forged branch outlets are generally manufactured conforming to MSS SP-97. They can be applied to piping codes including ASME B31.1, B31.3, B31.4 and B31.8. In order to be used within the established ratings, the forged branch outlets shall be design proof tested in accordance with ASME B16.9, MSS SP-97, or ASME BPVC Section VIII, Division 1, UG-101.

The forged branch outlet can be mounted perpendicular (90°) or lateral (45°) to the run pipe. It shall be attached to the run pipe at an opening by means of a full penetration weld. The dimensions are provided in two unit systems: US customary unit or SI metric unit.

The forged branch outlets can be made from forgings, bars, or seamless tubular products. The material shall conform to the requirements of WP grade seamless construction materials in ASTM specifications.

The sizing of integrally reinforced forged branch outlet are contain in the standard MSS SP-97 for different Classes of the fitting. Variety of attachment welds are permit in acc. to the applicable Pressure vessel or Piping codes. Typical branch attachments are shown in ASME 31.1, Figure 127.4.8-5 and ASME B31.3 Figure 328.5.4(F)

ASME B31.1 – Process Piping

Design Details in Paragraphs 104.3.1 and Figure 127.4.8-5

ASME B31.3 – Process Piping

Design requirements in Paragraphs 304.3 and Figure 328.5.4(F)

Paragraph 326: Dimensions and ratings in acc. to MSS SP-97

ASME B31.8 – Gas Transmission and Distribution Piping Systems

Paragraph 831.3.2 Special Fittings. When special cast, forged, wrought, or welded fittings are required to dimensions differing from those of regular shapes specified in the applicable ASME and MSS standards, the provisions of paragraph 831.3.6 shall apply.

Paragraph 831.3.6 Pressure Design of Other Pressure-Containing Components. Pressure-containing components that are not covered by the standards listed in Mandatory Appendix A (MSS SP-97 is not listed) and for which design equations or procedures are not given herein may be used where the design of similary shaped, proportioned, and sized components has been proven satisfactory by successful performance under comparable service conditions. In the absense of such service experience, the pressure design shall be based on an analysis consistent with the general design philosophy embodied in this Code and substantiated by at least one of the following:
(a)  proof tests, as described in UG-101 of Section VIII, Division 1 of the BPV Code
(b)  experimental stress analysis, as described in Annex 5.f of Section VIII, Division 2 of the BPV Code
(c)  engineering calculation


Each fitting shall be permanently marked with the required identification by raised lettering, and/or by stamping, electro-etching or vibro tool.

The minimum scope of marking:

  • Manufacturer’s name or trademark
  • Material Identification
  • Class (PN)
  • Run NPS (DN) Outlet NPS (DN)

ASME BPVC Section VIII Div. 1

In according Table U-3, Factory‐Made Wrought Buttwelding Fittings in acc. to B16.9 and Forged Fittings, Socket Welding and Threaded in acc. to B16.11 are accepted.

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