What are slip-on flanges, and When do we use slip-on flange?

Slip-on flanges are available at a lower cost and hence preferred by several contractors. The product holds ample of

strength and works even under fatigue conditions as that of the weld-neck flange. The slip-on flange can work well after

attaching to the end of a pipe or pipe fitting. The product is fit in easily, or the end of the pipe is set back easily by

the thickness of the pipe wall plus 1/8 of an inch. It allows easy installation without putting effort and damaging to the

flange face. The outer side of the flange is welded with a fillet weld.

Features of Slip-on flanges

These are flanges available at less cost. They have a low hub as pipe slips into the flange before performing welding.

These slip-on flanges are easy to align welded, both internally and externally.

Types of Slip-on flanges

There are various types of Slip-on flanges, including the Slip-On

Reducing Flange, raised face slip-on flange, and RTJ slip-on flange. The flange is applicable for reducing the line size and

limitation of the space limitations. These flanges work along with the weld neck flange and reducer combination. They are

useful when the flow is directed from the smaller size to the larger size. Slip-On flanges are welded internally and

externally. The welding offers them the ability to prevent leakage and sufficient strength.

Uses of Slip-on flanges

Slip-on flanges are primarily applicable for fluids working at low pressure. Also, these flanges work well with little

chance of leakage. These flanges work well in cooling water lines, firefighting water lines, and low-pressure compressed

airlines. Along with this, slip-on flanges are suitable in process lines to maintain the stream of steam, oil, gas,

condensates, etc. These flanges are applicable for low pressure and higher temperature system.

Common Uses and Features of Blind Pipe Flanges

Blinds are flanges without a center bore (hole or opening) and are

available in both Raised Face (RF) and Flat Face (FF) styles. While most flange types create a connection point that allows

the flow of liquid, gas, or air, blind flanges are used to seal the end of a piping system and prevent flow. Blind flanges

may be used when testing pipe pressure, to create an access point in a piping system, to temporarily seal a piping system

while modifying or repairing the line, or to create a long-term seal to terminate a piping system.

A blind flange is bolted, rather than welded in place. This allows easier access as needed for pipe system upkeep,

inspection, or to allow for future expansion. Pairing with a gasket creates a tight seal: The gasket fills the space between

the flange faces, which prevents liquid or gas leaks.

How to Choose the Right Blind Flange

Blind pipe flanges may be produced to match bolt hole measurements for slip-on or weld neck flanges, or if needed, can be

custom machined to any other specifications. Either way, when purchasing flanges, choose the appropriate flange features,

material, dimensions, and class to meet your application needs.

Find the Best Blind Flange Material for the Job

When choosing blind flanges, you must consider the best flange material and dimensions in relation to the piping

standards and requirements of your intended application. Generally, your flange material should match the connecting pipe

material. The most common blind flange materials are steel and stainless steel.

Steel is preferred for strength. API International stocks blind flanges in both forged and plate steel.

Stainless steel flanges are also available in forged or plate varieties in 304L and 316L. Stainless steel flanges are

often preferred for corrosion resistance.

In many cases, import material is acceptable to save on cost – in these cases, the flanges will still meet all the

standards for pressure applications. In instances where domestic flanges are specified, API International manufactures

flanges meeting “Buy American” or meeting American Iron and Steel Institute (AISI) requirements.

Plate flange vs slip-on flange

A plate flange is a flat, circular disc welded to a pipe’s end

enabling the flange to be bolted to another pipe. It is often referred to as flat flange, plain flange and flange slip, etc.

Two plate flanges can be bolted together with a gasket in between them, usually used in fuel and water pipelines.

The length of the pipes is not always known while constructing a pipeline. The plates may also be welded with a slight

bias to the shaft, allowing two pipes that might not be perfectly matched up to be joined.

Plate flanges have a serrated finish on the inner mating surface allowing the plate to fit within the material of the

gasket. In any given dimension, plate flange designs are standardized regardless of the materials used to manufacture them.

This ensures it exactly fit a 6-inch (15 cm) black pipe flange to a 6-inch stainless steel flange. This guarantees a perfect

seal between the two connecting pipes.

Slip-On flanges also known as SO flanges, or reducers, long-tangent elbows, and swags are built to slip over the outside

of the pipe. The flange has low vibration and shock resistance. Aligning a slip-on flange is simpler than any other flange.

The slip-on flange is suitable for applications with low pressure as the strength is around one third that of a weld neck

flange when under internal pressure. The Slip-on flange features an elevated profile.

Slip flanges or SO flanges are typically lower in cost hence making a common choice for the customers. A fillet weld is

often welded to the back or exterior of the slip-on flange or SO flange. Because of their lower initial cost, they are

favored over other flanges by many consumers, but the final installation cost is possibly not much less than that of the

other flanges due to the additional welding involved.

Threaded Flanges
Threaded flanges are widely demanded as pipe flanges used in different industrial applications. They are the special type of

pipe flanges which can be attached to the pipe without welding. Threaded flanges are threaded in the bore which match an

external thread on the pipe.

These threads are tapered in order to create a seal between the threaded flange and the pipe as the tapers approach the

same diameter. Sometimes a seal weld is also used together with the threaded connection. They are available in various sizes

and materials.
Uses of threaded flanges:

Threaded flanges can be fitted to pipes of various sizes without welding and this is one chief benefit for which these

flanges are highly demanded.

They can be used in extremely high pressure applications, particularly at or near atmospheric temperature, where the

necessary post weld heat treatment is not possible.

They are ideal for small diameter piping applications.

They are economical and time saving devices.

These threaded flanges are normally designed for non-cyclic applications.

The flanges are suitable to be used in applications where welding is hazardous.

They can be used in highly explosive areas.

Lap Joint Flanges

Lap Joint flanges are used on piping fitted with with lapped pipe or with lap joint

stub ends. The lap joint flange with the stub end assembly are normally used in systems requiring frequent dismantling for

inspection and cleaning and where the ability to swivel flanges and to align bolt holes materially eases the erection of

large diameter or unusually stiff piping. These flanges are also used in applications where there is a need to facilitate

bolt alignment.

These type of flanges are similar to slip-on flanges. The only difference is that it has a curved radius at the bore and

face to accommodate a lap joint stub end. They may be used at all pressures and are available in a full size range. These lap

joint flanges slip over the pipe, and are not welded. They are otherwise fastened to it. Here the bolting pressure is

transferred to the gasket by the pressure of the flange against the back of the pipe lap.

Advantages of Lap Joint Flanges:

Lap Joint FlangesLap Joint flanges have certain special advantages over other flanges. These are as follows:

Lap Joint flanges have the freedom to swivel around the pipe. This facilitates the lining up of opposing flange bolt


Lack of contact with the fluid inside the pipe leads to the greater durability of these flanges.

In piping systems which corrode or erode quickly, the lap joint flanges may be salvaged for re-use.

The pressure-holding capacity of lap joint flanges is little. But it is better than that of slip-on flanges.

The Lap Joint works as a backing ring on the stub.

The main advantage of lap joint flange is that the bolt holes can be aligned with the matching flange after the welds

have been completed.

They allow rotational alignment capability.

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