What is a buttweld stub end?
It is a buttwelded fastener that can form a flanged connection when combined with a lap joint flange. Alternatively, this buttweld fitting could be used in combination with a weld neck flange to form such connections. A Buttweld Stub End may be referred to as a lap joint or a Vanstone flared lap.
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Difference between long and short stub end
Short patterned fittings are referred to as MSS-A stub ends because they have a shorter hub length. When used as an alternative to weld neck flanges, they act as rotating backup flanges. Contrasting the short flanges, an ASA-A or long neck stub end is produced with an elongated hub.
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What are stainless steel stub ends used for?
The main purpose of a stub end is to form flanged connections by lowering the cost of the application. Stainless steel Stub Ends are often combined with flanges made from expensive materials like a duplex or super duplex alloys. As they are a two-part component that forms a flanged connection, a sturdy stainless steel grade can exhibit high tensile strength by effectively reducing the cost of the application. Another reason to use this alloy is that it can be used in elevated or cryogenic temperatures even in high-pressure environments. As long as the fitting can meet the requirements of the specifications, it can function in demanding applications. The corrosion resistance properties are another factor that makes them useful in highly corrosive industries like oil and gas, shipbuilding, chemical processing, petrochemical processing, construction, pulp and paper.
Long collar stub end & pipe stub end sizes and tolerances as per ASME B16.9
Stub end manufacturing process
Typically, a stub end is produced by hot forming. The mandrel technique is commonly used to manufacture these fittings. In this process, a seamless or welded pipe is first to cut into pieces. After the pipe is cut into the desired length, it is pushed over a die (known as a mandrel). A hydraulic pump aids in pushing the pipe over the mandrel, causing the pipe to simultaneously bend and expand. Once the fitting is shaped, its surface is treated, followed by the application of a suitable coating (depending on the requirement of the properties).
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Benefits of lap joint stub ends
Stub ends offer two advantages- low cost and convenience.
Though the flange used is produced from an expensive material, a stub end only needs to have the necessary mechanical strength or corrosion resistance properties to withstand an application. So typically materials like stainless steel, carbon steel or alloy steel stub ends are paired with flanges made from duplex, super duplex grades or higher. In applications with larger nominal diameters, this is a cost-effective solution, that brings down the cost by a considerable margin.
Apart from reducing the overall cost of the flanged connection, they permit the lap joint flange to revolve easily. Revolution in turn helps the flanges to align with the bolt holes of the opposite or mating flange.
NDT test done for backing flange and stub end to ensure leak-free connection, contact us for more information!
Common types of carbon steel stub end
These fittings are available in three different variations –
- Type A stub ends are manufactured and machined such that they can match a conventional lap joint backing flange while forming a flanged connection. The mating surfaces of these fittings have an identical profile. This helps to ensure the flare face is loaded very smoothly.
- Type B stub ends, like Type A are produced by forging pipe fittings. Typically, they are used with slip-on flanges.
- Type C stub ends are produced from pipes. Unlike the other two types, these fittings can be used with both a lap joint or slip-on flange.
How to install stub end with backing flange?
The first step to installing a flanged connection is to slip a lap flange onto its corresponding stub end. After mounting the flanges, the stub ends are welded with the approved techniques onto a pipe spool by a qualified welder. Once they are welded, the area is cleaned to reduce the risk of corrosion. As the fitting is welded to the pipe spool, the lap joint flange can now freely revolve around the stub end. The flanges are to be mated once the bolt holes of both lap joints are in proper alignment.