Views: 7 Author: Monica Publish Time: 2025-09-28 Origin: Site
MSS SP 97 weldolet is a butt-weld fitting used for connecting branch pipes. It is typically used in high-pressure, high-temperature, large-diameter, and thick-walled piping systems. The fitting body is typically manufactured from a material that matches the main pipe material, with common materials including carbon steel, alloy steel, and stainless steel.
The core structure reinforces the main pipe opening through a saddle-shaped joint and reinforced areas, effectively reducing stress concentration and improving the overall reliability and safety of the piping system.
MSS SP 97 specifies the design, dimensions, testing, and material strength requirements for pipe branches, commonly known as "olets."
The core of this standard is the definition of a pipe geometry that provides integral reinforcement. This means the fitting inherently provides the necessary cross-sectional area reinforcement required by piping codes such as ASME B31.3, effectively reducing stress concentration areas. This design allows engineers designing high-pressure or high-temperature piping systems to avoid lengthy and complex reinforcement area calculations and directly use standard-compliant fittings.
MSS SP 97 covers three types of fittings (butt-weld, socket-weld, and threaded). Butt-weld fittings (socket-weld sockets) are classified by pipe schedule (STD, XS, SCH 160), while socket-weld/threaded fittings (socket-weld sockets/threaded sockets) are classified by pressure class (3000#, 6000#).
MSS SP 97 covers 90-degree and 45-degree branch fittings, including butt-weld, sockolets, and threaded types. Socket-weld weldolets are designed specifically for butt-weld connections and typically have a beveled end, making them suitable for butt welding of main and branch lines.
Weldolet is primarily used for pipe branch connections, replacing traditional reducing tees. Its structure consists of a main pipe connection, a reinforced section, and a branch pipe connection, enhancing pipe safety and reliability under high pressure, high temperature, and frequent loads.
The weldolet is welded to the main pipe, while connections to branches or valves are made using butt welding, socket welding, or threaded connections.
Manufactured in strict accordance with MSS SP97 standards, the weldolet's core advantages include reduced pressure through optimized fluid flow, simplified installation, lower overall costs, and a range of standard sizes. Consequently, the weldolet is widely used in the oil, power, and nuclear power industries, particularly in applications where the main pipe diameter is large or where high-strength branch connections are required.
To accurately understand and measure the weldolet, you first need to master the following key dimensional parameters.
The primary dimensions used in the MSS SP 97 Weldolet Dimension Chart are defined as follows:
Dimension A (Height): This is the height of the fitting, measured from the bottom where it contacts the main line to the center of the outlet. It is the primary reference dimension for calculating the total run length (L).
Dimension B (Bottom Width/Outline Diameter): This is the outside width or diameter of the fitting where the bottom meets the main line profile. This dimension must be designed to precisely match the specific outside diameter (OD) of the main line to ensure a snug fit.
Dimension C (Outlet OD): This is the outside diameter of the butt-weld end of the branch pipe connection. This dimension is generally closely related to the required opening diameter for installation on the main line. For example, for a standard NPS 4 socket-weld socket, the C dimension is approximately 4 3/4 inches (120.65 mm).
Dimension D (Outlet Inside Diameter/Bore): This is the inside diameter of the outlet connection. In sockets of the same size, this dimension should match the nominal inside diameter of the connected branch pipe. Dimension L (Total Installation Length/Face-to-Crotch Length): This is the calculated total installation length, typically quoted on layout drawings. It is calculated using the following formula: L = A + (Main Pipe OD/2) + Root Gap.
Sch 40 MSS SP 97 Weldolet Dimensions Chart
NPS | A (inch) (mm) | B (inch) (mm) | C (inch) (mm) | Weight (pound) (Kilogram) |
1/2 | 3/4 [19.05] | 1 3/8 [34.93] | 15/16 [23.81] | 0.15 |
3/4 | 7/8 [22.23] | 1 5/8 [41.28] | 1 3/16 [30.16] | 0.25 |
1 | 1 1/16 [26.99] | 2 1/8 [53.98] | 1 7/16 [36.51] | 0.40 |
2 | 1 1/2 [38.10] | 3 1/2 [88.90] | 2 9/16 [65.09] | 1.50 |
4 | 2 [50.80] | 6 [152.40] | 4 3/4 [120.65] | 6.70 |
8 | 2 3/4 [69.85] | 10 3/8 [263.53] | 8 11/16 [220.66] | 14.00 |
14 | 3 1/2 [88.90] | 16 1/8 [409.58] | 14 1/16 [357.19] | 31.75 |
Sch 160 MSS SP 97 Weldolet Dimensions Chart
Outlet size (inch) | A (inch) | B (inch) | C (inch) | Weight (pound) |
1/2 | 1 1/8 | 1 3/8 | 9/16 | 0.25 |
3/4 | 1 1/4 | 1 3/4 | 3/4 | 0.70 |
1 | 1 1/2 | 2 | 1 | 0.85 |
1 1/2 | 1 5/8 | 2 3/4 | 1 5/16 | 1.60 |
2 | 1 7/8 | 3 1/4 | 1 5/8 | 2.80 |
Branch Pipe NPS | Weight (kg) | Branch Pipe NPS | Weight (kg) |
1/2 | 0.068 | 5 | 3.85 |
3/4 | 0.113 | 6 | 6.35 |
1 | 0.181 | 8 | 12.70 |
1 1/4 | 0.317 | 10 | 17.69 |
1 1/2 | 0.362 | 12 | 29.48 |
2 | 0.680 | 16 | 41.73 |
2 1/2 | 1.02 | 20 | 79.37 |
3 | 1.70 | 24 | 127.0 |
1. Preparation
Before installation begins, thoroughly inspect all materials to ensure that the material, dimensions, wall thickness, and specifications of the Weldolet fitting, main pipe, and branch pipes comply with the design drawings and welding specifications. Clean all welding areas to remove any impurities such as oil, rust, scale, and coatings. Polish the Weldolet groove and main pipe surface to a bright metallic color to ensure weld quality.
2. Marking and Positioning the Hole
According to the design drawings, accurately mark the Weldolet installation location and centerline on the main pipe. The bottom surface of the Weldolet saddle should align with the outer wall of the main pipe, and the outlet centerline should be perpendicular to the main pipe centerline. Using appropriate tools, cut a connecting hole in the main pipe at the marked location to match the Weldolet's inner diameter. After cutting, thoroughly grind the hole edges to remove burrs and slag, ensuring a smooth opening. Verify that the hole profile meets specification requirements.
3. Weldolet Alignment and Securing (Spot Welding)
Place the weldolet over the main pipe opening, ensuring its base contour closely matches the main pipe's outer wall. Use specialized tools (such as shims) to create an appropriate welding gap between the weldolet base and the main pipe. After confirming the weldolet's axial orientation and verticality, perform multiple symmetrical spot welds to temporarily secure it to the main pipe to prevent displacement or deformation during the actual welding process.
4. Preheating
For certain high-strength steels or thick-walled pipes, or when welding at low temperatures, the main pipe and weldolet in the welding area must be preheated according to welding requirements. The preheating temperature should be accurately controlled using a temperature probe or thermocouple and maintained within the temperature range specified in the WPS to slow cooling and reduce the risk of cold cracking.
5. Main Welding
First, perform the root pass, followed by the filler and cap passes to achieve the desired weld thickness and strength. During the welding process, symmetrical segmentation and skip welding techniques should be used, and interpass temperatures should be strictly controlled. The welds between the weldolet and the main pipe should be full-circumference fillet or groove welds.
6. Post-weld Treatment and Inspection
After welding, the weld seam and adjacent areas must be thoroughly cleaned of slag, spatter, and oxides. After the weld has cooled to room temperature or the temperature specified in the WPS, post-weld heat treatment should be performed according to specification requirements. Subsequently, the weld must undergo non-destructive testing to ensure that it is free of internal and surface defects.
7. Branch Pipe Connection and Pressure Testing
After the welds between the weldolet and the main pipe have passed inspection, the branch pipe should be connected to the outlet of the weldolet. Finally, the entire piping system must undergo a hydrostatic or pneumatic pressure test according to the design pressure and specification requirements to verify the tightness and structural integrity of the weldolet connection area and the entire system. Only after passing the test can it be put into operation.
