---
title: What Is the Meaning of SO Flange?
date: 2025-06-25T14:48:38Z
modified: 2025-06-25T14:48:41Z
permalink: "https://www.longanflange.com/blog/what-is-the-meaning-of-so-flange/"
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status: publish
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  - Blog
featured_image: "https://www.longanflange.com/wp-content/uploads/2024/07/088b641a27848805159c.jpg"
featured_image_alt: stainless steel flanges manufacturer longan Slip-On Flanges
timestamp: 2025-06-25T14:48:41Z
tags:
  - Blog
---

If you’re specifying flanges for pipe systems and see “SO flange,” you’re looking at a **Slip-On flange**. Unlike some high-cost options, SO flanges slide over the pipe and are joined with fillet welds—inside and out—making them easy to align and install in low- to medium-pressure systems.

## **How SO Flanges Work**

Slip-On flanges have a slightly larger bore than the pipe, allowing them to slide over it before being welded on both sides. After welding, you add bolts and a gasket to complete the seal.

- **Easy installation:** The flange simply slides on before welding, making alignment easier compared to flanges requiring more precise fit-up.
- **Good leak resistance:** Once properly welded inside and out, slip-on flanges offer solid sealing, especially in smaller-diameter piping.

## **What Makes SO Flanges Popular**

Slip-On flanges have several advantages that make them stand out:

- **Lower cost**: Their flat design and simple manufacturing process reduce material and machining expenses.
- **Easy alignment**: They don’t require the same tight fit as weld-neck types, speeding up installation and reducing labor.
- **Reliable for standard service**: When used within recommended pressure and temperature ranges, the inner and outer welds provide a dependable seal, especially in smaller-diameter pipes.

These features make SO flanges a practical choice for a wide range of industrial systems.

## **Choosing the Right SO Flange for Your System**

Before specifying a slip-on flange, make sure each detail matches your project requirements:

- **Match pipe dimensions**: The flange should correspond to your pipe’s nominal diameter and wall thickness suited for your system’s conditions.
- **Gasket and face compatibility**: Slip-on flanges can use raised face or flat face gaskets based on your pressure and sealing needs.
- **Bolt alignment**: Most Slip-On flanges follow ASME (B16.5, B16.47) or DIN standards, so check that the bolt-hole spacing matches the connected components.
- **Material selection**: Choose the right material for your fluid and operating conditions—stainless steel flanges resist corrosion, while carbon steel options are more cost-effective. Check out Longan’s[ stainless steel flanges](https://www.longanflange.com/wp-content/uploads/wp-mfa-exports/page/stainless-steel-flange.md) or [ASME-grade options](https://www.longanflange.com/wp-content/uploads/wp-mfa-exports/page/asme-flange.md) if you need compliance with U.S. standards.

## **When Slip-On Flanges Aren’t the Best Fit**

While SO flanges cover many use cases, they’re not suitable for everything. Avoid them in applications that require:

- **High-pressure systems** where stronger weld-neck flanges offer better structural support.
- **Frequent temperature or pressure cycling**, which can weaken welds over time.
- **Large-diameter piping**, where the welded structure of other flange types performs better under stress.

In such cases, options like weld-neck or socket weld flanges may be more appropriate.

## **What Is the Meaning of SO Flange: Final Takeaway**

What is the meaning of SO flange? A slip-on flange offers simplicity, affordability, and reliable performance for low- to mid-pressure applications. They’re a solid option when alignment and cost are top priorities.

If you’re sourcing for stainless or ASME-grade systems, [Longan Flange](https://www.longanflange.com/wp-content/uploads/wp-mfa-exports/page/about.md) carries a full line of certified [slip-on flanges](https://www.longanflange.com/products/slip-on-flange/) built to industrial standards.

[Reach out ](https://www.longanflange.com/wp-content/uploads/wp-mfa-exports/page/contact.md)if you’d like help matching one to your specifications!