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Weldolets: A Comprehensive Guide

A Weldolet fitting ranks among the most common types of piping components and is classified as an Olet. It serves the purpose of creating branch connections from run pipelines to branch pipelines, primarily through the utilization of a butt weld welding process, creating a 90° branch connection. In Weldolets, both ends are typically beveled, making them particularly suitable for connecting large-bore to small-bore pipes in high-pressure service applications, especially those exceeding 2 inches in diameter.

Weldolet fittings are compatible with butt weld connections, mirroring the outlet pipe to minimize stress and provide added reinforcement for the connection. It's crucial to maintain the same or higher schedule for Weldolet fittings compared to the branch run pipes to ensure heightened strength. Weldolets come in both full size and reducing size variants, with the former matching the size of the run or header pipe (e.g., a 4-inch to 4-inch branch connection) and the latter having a branch size smaller than the run or header pipe (e.g., 4-inch to a size less than 4 inches). Several common standards and codes govern the selection of Weldolets, including ASTM A234, MSS SP-75, and ASTM A403. In some instances, standard TEE fittings are used in place of Olets, but Olets remain a preferred choice due to their cost-effectiveness, lightweight nature, and ease of welding.

Weldolets find their application in scenarios where the branch pipe's bore size is smaller than that of the header or run pipe. Another method for branching pipe connections is through RF pad welding, but this approach tends to be bulkier and less cost-efficient. Olets are designed according to the dimensions stipulated in the Piping Code ASME B31.3. These fittings, sometimes referred to as Branch Connection Fittings or Outlet Fittings, encompass 12 different types of Olets available in the market, with Sockolet being widely recognized and employed as a socket fitting, typically fabricated or accessible in Class 3000#, 6000#, and 9000#.

Features of Weldolets

  • Weldolets have beveled ends on both the run and branch sides, which makes them easy to weld to the run and branch pipes.

  • Weldolets are available in a wide range of sizes and schedules, making them suitable for a variety of applications.

  • Weldolets are strong and durable, and they can withstand high pressures and temperatures.

  • Weldolets provide a smooth transition between the run pipe and the branch pipe, which helps to reduce stress concentrations and improve flow efficiency.

Applications of Weldolets

Weldolets are used in a variety of industries, including:

  1. Oil and Gas: Weldolets are used extensively for connecting branch pipelines to the main lines. They are ideal for both high and low-pressure applications.

  2. Petrochemical Industry: Weldolets are commonly employed in refineries, chemical processing plants, and other petrochemical facilities to facilitate branching off pipelines for different processes.

  3. Power Plants: Power generation facilities often use weldolets to connect auxiliary pipelines for coolant systems, steam, and other applications.

  4. Water and Wastewater: In water treatment and distribution systems, weldolets are used to create branch connections for various purposes, such as adding valves, meters, or other components.

  5. HVAC Systems: Weldolets can be found in heating, ventilation, and air conditioning systems for branching off ducts or pipes.

Benefits of Using Weldolets

Strength and durability: Weldolets are made of high-quality materials and are designed to withstand high pressures and temperatures.

Smooth transition: Weldolets provide a smooth transition between the run pipe and the branch pipe, which helps to reduce stress concentrations and improve flow efficiency.

Ease of installation: Weldolets are relatively easy to install and weld.

Versatility: Weldolets are available in a wide range of sizes and materials, making them suitable for a variety of applications.

When to Use a Weldolet

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.

Olet types

Olets are a diverse range of fittings designed to create branch connections from primary pipelines. Here's an overview of various Olet types:

  1. Weldolet: A widely used branch connection fitting, featuring a 90° branch connection, which is typically attached through butt weld welding.

  2. Sockolet: Similar to Weldolet, Sockolet is equipped with a socket weld outlet, ideal for high-pressure applications.

  3. Insert Weldolet: This Olet variant offers a smooth transition between the run pipe and branch pipe, reducing turbulence and stress.

  4. Elbolet: As the name suggests, Elbolet creates a 90° branch connection, but it is designed for smaller bore pipes.

  5. Threadolet: Featuring a threaded outlet, Threadolet is suitable for low-pressure applications, commonly used in smaller-diameter pipes.

  6. Flexolet: This flexible Olet allows for some movement and alignment, making it useful in applications where there is potential for pipe shifting.

  7. Sweepolet: A branch connection fitting designed with a gentle, sweeping curvature to reduce stress concentration, often used in high-pressure piping systems.

  8. Brazolet: Primarily used for joining small bore pipes to larger bore pipes, Brazolet is a cost-effective and efficient branch connection.

  9. Coupolet: Coupolet combines a socket-weld or threaded connection with a welding connection for versatile use.

  10. Latrolet: Ideal for lateral connections, Latrolet creates branch connections at a 45° angle from the main pipe.

  11. Nipolet: A combination of Weldolet and Nipple, Nipolet is used for larger branch connections and maintains structural integrity.

Weldolet Selection Criteria

  • Title and Complete Specifications

  • Pressure Class Rating/Pipe Schedule

  • Types of Olet

  • Type of End Connection

  • Material of Construction

  • Dimension Standard

  • Design Standard

  • Steam Services Requirement

Installing Weldolets

  1. Pipe Preparation: The main pipeline and branch pipe are meticulously prepared, with the main pipeline generally requiring a beveled end to facilitate welding.

  2. Welding: Weldolets are expertly welded onto the main pipeline, utilizing appropriate welding methods like MIG, TIG, or stick welding.

  3. Threaded or Socket Welding: The branch pipe is securely connected to the weldolet using the threaded or socket weld connection, depending on the specific weldolet type used.

  4. Inspection: A rigorous inspection is carried out to ensure the welds are of top quality, free from leaks or defects.


Weldolets are a versatile and reliable type of pipe fitting that can be used in a variety of applications. They are strong and durable, provide a smooth transition between the run pipe and the branch pipe, and are relatively easy to install and weld. When selecting and welding weldolets, it is important to consider the applicable standards and codes.

Universal Engineering services(UES) can do Engineering of modular substations. Our Structural Engineers can design offshore container modules, skids packages, cargo baskets, steel structural frames, lifting analysis of offshore structures,etc to clients all over the middle east countries like UAE, Oman, Qatar, Saudi and Kuwait for petrochemical, power and oil and gas industry. We also offers reliable offshore and onshore design of structures as per D.N.V. 2.7.1 and we are diversified into Structural Design, Engineering & Analysis for the Industrial, Offshore and Oil & Gas industry.

**The content of this article is taken from web open source. The blogs are intended only to give technical knowledge to young engineers. Any engineering calculators, technical equations and write ups are only for reference and educational purpose.

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