Slip on flanges are a popular type of pipe flange designed to accept pipe into the bore/center of the flange for welding around both the Outer Diameter (OD) of the pipe and on the interior side of the connection. You may recognize them:
The slip-on flange is a simple and excellent alternative to a weld neck as it does not have a weld bevel, and therefore allows the pipe to be adjusted in length relative to its position of the flange. The bore of the slip on will give ample amount of space for the matching pipe. This allows for enough working space for the welder and fabricator to make the connection.
This flange type is extremely common in lower pressure applications. Most slip on style flanges will have a hub which will often appear similar dimensionally to a raised face. It can be furnished without a hub if space is limited and the application allows for a “ring style” slip on. Although the hub style is more common when referring to a slip on, a ring style slip on without a hub still falls under the category of a slip on flange, and can be called out as you desire. Slip ons in higher pressure classes are often made with the height of a lap joint for a better connection. If the hub height is not a concern and a lap joint is not readily available, customers will sometimes opt for a slip on made to a lap joint style with a machined hub.
Slip on flanges are more commonly found in lower pressure assemblies and become less utilized when a higher stress service calls for a superior connection to the piping assembly. This is because a slip on style flange will accept a pipe with a fillet weld connection, whereas a weld neck flange will have a reinforced hub at the base and form a weld bevel connection directly to the butt weld end of a pipe. This tapered hub allows for stronger service in a mechanical stress environment.
The Weld Neck Flange vs Slip On Flange
The Weld Neck Flange is easily recognizable by the hub that gradually tapers from the bolted connection to the pipe. At the Point of Weld on the Weld Neck it is supplied with a specific bore to mate with the attaching pipe or fitting. This connection is made with a full penetration butt weld, this prevents turbulence at the joint, reduces erosion and restriction to product flow. The Weld Neck Flange offers increased strength under higher pressures, subzero or elevated temperatures that cause line expansion or retraction or other variable forces. The Slip On Flange is connected to the pipe by two welds, one on the back side of the Flange and one on the inside of the Flange. The inside weld of the Flange to the pipe is recessed a minimum of the wall thickness plus 3 millimeters or 3/16” of an inch. This is to avoid damage to the gasket seating surface or face. Although the initial cost of a Slip On Flange is slightly less than a Weld Neck Flange, you have two welds one on the back side and one on the inside of the Flange and the added inspection of the second weld doubling weld and inspection cost. The Slip On Flange is designed to be welded to pipe then a fitting as fittings are designed for butt weld connections. The calculated strength of a Slip On Flange under internal pressure is about two thirds that of a Weld Neck Flange, and their life under fatigue is about one third that of a Weld Neck Flange.
Common Uses and Features of Blind Pipe Flanges
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.
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.
Blind flanges are available in the same pressure classes and bolt hole patterns as other flange types, but they tend to be thicker. To determine the appropriate blind flange size, important measurements include the outer diameter (OD), bolt hole circle (BHC), bolt hole diameter, and thickness. While most flanges are round, square blind flanges may be used to close off hydraulic piping systems.
Blind flange dimension requirements and materials specifications are designated under AWWA C207 and C228, and ASME B16.5 and B16.47. The general dimensions by blind flange type are included in the chart below, and you can refer to the tables on individual flange listings to determine more specific measurements—such as thickness—based on diameter and pressure rating.
The Differences Between Forged Flanges and Cast Flanges
Flanges can either be forged or cast. Both manufacturing methods have their advantages and disadvantages, depending on the application you have in mind for your flange. Here at Texas Flange, we primarily deal with forged flanges due to the outdated nature and lower standard of quality of cast flanges. Below, we will delve into the advantages and disadvantages of both forged steel flanges and cast iron flanges.
Casting is the process in which the metal is heated until molten then poured into a mold or vessel to create the desired shape. They are often used in cases that are too large, complicated, or other wise not suitable for forgings. Some of the advantages of flanges manufactured in this way include lower costs of production, the ability to make more intricate parts at lower costs, as well as having no true upper limit on size when it comes to your part.
There are, however, some drawbacks to cast iron flanges. The most important of these being how susceptible they are to internal defects. Due to this, cast flanges are not suitable for high pressure applications or applications in which the probability of corrosion is high. Despite advancement of casting technology and computer optimization of the casting process and designs, it is still difficult to meet the standards required for petrochemical industry applications.
Forging is the application of mechanical and thermal energy to steel billets or ingots to cause material to change its shape while still in solid form. Forgings offer consistency in composition and structure. Due to the nature of the production of forged flanges, the production costs are higher than that of cast flanges. Though they cannot have the complex shapes that cast flanges can be made in, their internal structure is more compact and therefore seldom have the defects the often affect cast flanges. Forging eliminates defects found in casting such as shrinkage, porosity, cavities, or cold pour issues.
Generally, forged flanges are stronger and more reliable than cast flanges because the grain flows of the steel are altered, confirming to the shape of the part. The tight grain structure of forgings makes the pieces mechanically stronger, and more resistant to general wear and tear than cast flanges. The higher quality, reliability, strength, and durability are why we deal mostly in forged flanges rather than cast flanges.
Threaded Flanges
Threaded Flanges are also known as screwed flange, and it is having a thread inside the flange bore which fits on the pipe with matching male thread on the pipe.
This type of joint connection is Speedy and simple but not suitable for high presser and temperature applications. Threaded Flanges are mostly used in utility services such as air and water.
Threaded (Screwed) flange is similar to the Slip-On flange, but the bore is threaded. Its chief merit is that it can be assembled withour welding, explaining its use in low pressure services at ordinary atmospheric temperatures, and in highly explosive areas where welding create a hazard.
Threaded flanges are threaded in the bore which match an external thread on the pipe. Threaded flanges are used with pipes that have external threads. The benefit of these flanges is that it can be attached without welding.
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.
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