08,Sep 2024
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This guide will walk you through the steps to identify the correct dimensions and explore essential factors like flange thickness, pressure class, and the corresponding ANSI flange dimensions
Slip-on flanges are widely used in piping systems across industries. They are flexible, affordable, and easy to install.
A slip-on flange is designed to fit over the pipe, unlike other flange types that attach directly. By welding both the inside and outside of the flange, you create a secure and leak-proof connection. This design makes them ideal for lower-pressure applications.
One of the primary advantages of slip-on flanges is their ease of alignment during installation. Because the pipe slides into the flange, precise positioning is easier than with other types of flanges. This flexibility, combined with lower costs, makes them an attractive option for many industries. Examples of these are HVAC, water treatment, and chemical processes.
However, while the slip-on flange offers significant benefits, determining the right slip-on flange dimensions is of utmost importance. This is to ensure a piping system’s integrity. If dimensions are not accurately selected, you risk leaks, joint failures, and costly downtime.
When selecting the correct slip-on flange dimensions, it’s vital to consider several factors, including pipe size, pressure rating, and system requirements. Here’s a step-by-step approach to ensure accurate flange selection.
The first step is identifying the nominal pipe size (NPS). This refers to the diameter of the pipe the flange will connect to. NPS sizes are standardized and range from 1/2” to 24” for most slip-on flanges. Ensure that the slip-on flange dimensions match the pipe’s outer diameter to guarantee a proper fit.
Refer to our table below for a general reference about slip-on flange NPS:
| NPS | Outside Diameter | Number of Holes | Raised Face Diameter | Thickness |
| ½ | 3.50 | 4 | 1.38 | 0.44 |
| ¾ | 3.88 | 4 | 1.69 | 0.50 |
| 1 | 4.25 | 4 | 2.00 | 0.56 |
| 1 ¼ | 4.63 | 4 | 2.50 | 0.63 |
| 1 ½ | 5.00 | 4 | 2.88 | 0.69 |
| 2 | 6.00 | 4 | 3.63 | 0.75 |
| 2 ½ | 7.00 | 4 | 4.13 | 0.88 |
| 3 | 7.50 | 4 | 5.00 | 0.94 |
| 3 ½ | 8.50 | 8 | 5.50 | 0.94 |
| 4 | 9 | 8 | 6.19 | 0.94 |
| 5 | 10 | 8 | 7.31 | 0.94 |
| 6 | 11.00 | 8 | 8.50 | 1.00 |
| 8 | 13.50 | 8 | 10.63 | 1.13 |
| 10 | 16.00 | 12 | 12.75 | 1.19 |
| 12 | 19.00 | 12 | 15.00 | 1.25 |
| 14 | 21.00 | 12 | 16.25 | 1.38 |
| 16 | 23.50 | 16 | 18.50 | 1.44 |
| 18 | 25.00 | 16 | 21.00 | 1.56 |
| 20 | 27.50 | 20 | 23.00 | 1.69 |
| 22 | 29.50 | 20 | 25.25 | 1.81 |
| 24 | 32.00 | 20 | 27.25 | 1.88 |
Flanges are categorized by their ability to handle pressure, commonly referred to as the pressure class or pressure rating. These ratings are established by the ASME (American Society of Mechanical Engineers).
The most widely used pressure classes are 150, 300, 600, and 900, but for more demanding applications, they extend up to Class 1500 and 2500.
The pressure class of a flange signifies the maximum allowable pressure the flange can safely withstand at a specific temperature.
For instance, a Class 150 flange is designed for lower-pressure systems, while a Class 300 flange is rated to handle higher pressures, meaning it is built thicker and heavier to withstand more demanding conditions. Specifically, a Class 300 flange can safely manage 300 psi (20.6 bar) at its rated temperature
Slip-on flanges follow standardized dimensions as specified by ANSI (American National Standards Institute). These standards, particularly ANSI flange dimensions, ensure compatibility across different systems and manufacturers
To determine the correct ANSI flange dimensions for your project, refer to standards like ASME B16.5. The latter outlines the specifications for pipe flanges and fittings. These standards will provide detailed measurements for various aspects of the flange, such as:
The flange thickness is one of the most crucial dimensions when selecting a slip-on flange. Thicker flanges are necessary for systems operating under high pressure to prevent cracking or warping.
For example, an NPS 4” Class 150 flange might have a thickness of 1 inch, while a Class 600 flange of the same size could have a thickness of 1.8 inches.
Ensuring the right thickness is essential for maintaining the durability and safety of your piping system. A flange that is too thin may buckle under pressure, while an excessively thick flange can drive up costs without added benefits
Choosing the right material for slip-on flanges is essential to ensure compatibility with the system’s operating conditions. The most common materials used for these flanges include:
The material selected will significantly influence the slip-on flange specification. It should be chosen based on factors like temperature, pressure, and chemical compatibility with the fluid passing through the system.
Choosing the right slip-on flange dimensions is crucial for ensuring the long-term performance and safety of any piping system.
Based on this guide some practical steps you need to consider cover the following:
Careful attention to these details helps prevent costly failures and ensures a secure fit.
If you’re looking for high-quality flanges that meet all your industrial needs, Longan Flange is a trusted manufacturer. They have been in the industry for years offering a wide range of ANSI-compliant flanges. With a commitment to precision and durability, Longan Flange provides reliable solutions that stand the test of time.
References:
Flange Bolting Chart – ASME B16.5 (1)
SME B16.5 Pipe Flanges and Flanged Fittings (2)
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