ThePipingMart Blog flanges Loose Flange vs Slip-on Flange – What’s the Difference

Loose Flange vs Slip-on Flange – What’s the Difference

Loose Flange vs Slip-on Flange

Flanges are essential in pipe fittings as they provide a reliable and robust connection between two pipes. There are various types of flanges available in the market, and each one of them has its unique features and benefits. Two of the most commonly used flanges are loose flange and slip-on flange, but sometimes, it can be challenging to differentiate between these two. This blog post will discuss the difference between loose flanges and slip-on flanges to help you choose the best one for your project.

What is Loose Flange?

A loose flange is a device used in piping systems to tightly seal and connect two pipes. It consists of a metal ring with bolt holes along its circumference, allowing it to be securely bolted onto two existing pipes. A gasket or O-ring is typically placed between the flange and the connecting pipe surfaces to create a secure, water-tight seal. Loose flanges are commonly used for connections requiring frequent maintenance or removal, making them ideal for applications such as water filtration systems and valves.

What is Slip-on Flange?

A Slip-on Flange is a type of pipe flange that slides over the end of a pipe and is typically welded in place. It is thicker than other flanges, providing greater strength and durability in high-pressure applications. The face of the flange has an internal diameter slightly larger than the external diameter of the pipe, allowing it to easily slide over the end.

Difference Between Loose Flange and Slip-on Flange

Basic Definition

A slip-on flange, also known as a SO flange, is where the pipe slips into the flange and is welded on both sides. On the other hand, a loose flange, also known as a lap joint flange, involves two separate components – the stub end and the backing flange. The stub end slips over the pipe while the backing flange is attached to the mating flange using bolts.


Slip-on flanges have a slightly larger diameter than the pipe’s outer diameter, allowing them to slip over the pipe. They are available in raised-face and flat-face designs and are ideal for low-pressure applications. On the other hand, loose flanges consist of two parts – the stub end and the backing flange. These two components make the loose flange design flexible and adaptable to different pipe thicknesses and materials.


Slip-on flanges are typically made of carbon steel, stainless steel, or alloy steel, which makes them highly durable and corrosion-resistant. However, the material used for the loose flange depends on the material of the stub end, which is usually made of stainless steel, and the backing flange, which can be made of carbon or alloy steel.


Slip-on flanges are ideal for low-pressure and low-temperature applications such as water, gas, and drainage systems. They are also used in applications requiring frequent disassembly, such as testing systems. Loose flanges, however, are more commonly used in applications where alignment of the piping systems is essential, such as in heat exchanger piping, where thermal expansion and contraction can cause misalignment.


Slip-on flanges are generally more affordable than loose flanges due to their simple design and fewer components required. However, when it comes to replacing or repairing the flanges, slip-on flanges can be more expensive than loose flanges in the long run, as the pipe may require cutting and re-welding. Loose flanges are easy to replace and repair as the stub end can slide over the pipe without cutting it.


In summary, slip-on and loose flanges have unique features and benefits. Slip-on flanges are easy to install and cost-effective, making them ideal for low-pressure and low-temperature applications. Loose flanges, on the other hand, are flexible and adaptable and can withstand high pressures and temperatures. Additionally, they are easy to repair and do not require pipe cutting. Therefore, the choice between the two depends on your project’s specific needs and requirements. This blog post has helped you understand the difference between these two types of flanges.

Related Post