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As we know there are four connecting types for the pipe fittings: Socket weld, butt weld, threaded, and flanged.
In terms of steel pipe fittings that you would be able to use for your pipeline projects, you will find two of them to be quite popular: Socket weld fittings and butt weld fittings.
However, since both of them seem to have their own share of pros and cons, you might be confused about which one is best for your particular purpose. Because of this reason that we have taken the responsibility of drawing up a comparison between them. In this way you will know the differences of socket weld vs butt weld.
To know more about these, continue reading below.
A socket weld fittings is a pipe attachment detail. In this case, the pipe will be inserted in to a recessed area of a pipe, fitting, valve, or flange. In order to join the pipes or valves to the other sections of the pipe, seal welds of fillet type will be applied. So in some cases socket weld fittings is a good choice. This is because the benefits of great structural strength and high leakage integrity would be quite important factors that has to be taken in to consideration when designing your pipeline project.
In case you place an request for this kind fittings, you need to specify the OD dimensions and with pressure requirements (Or thickness schedule), socket weld fittings pressure ratings usually expressed in class 3000, class 6000, and class 9000.
Socket weld pipe fittings usually simplified as SW pipe fittings, so you will see some descriptions like SW elbow, SW tees, SW couplings etc.
Since these fittings have been termed to be high pressure, they could easily be used in a diverse range of industrial processes.
• Socket weld pipe fittings like elbow, tee, reducers, can be used at pipelines for conveying toxic, flammable, or expensive materials where there would be no scope for leakage to occur.
• Used in conjunction with ASME pipe and for to change to different dimensions.
• Applied in the places where pipe work has been deemed to be permanent. In addition, they have also been designed in a manner which could provide characteristics of good flow.
• Manufactured in accordance with ASTM A234 standards and also could be according to ASME B16.11. This is a standard covers dimensions, pressure-temperature ratings, marking, tolerances, and requirements for materials for carbon steel and forged carbon. In terms of material forms that would be acceptable, those could be bars, forging, seamless tubes, and seamless pipe which conform to the requirements of fittings chemicals, mechanical property, and practices.
Like butt weld fittings, based on material types, socket weld fittings also ranged as stainless steel pipe fittings, carbon steel and alloy steel. Based on applications, it includes socket weld elbow, socket weld tee, and reducing tee, reducers, couplings, and SW flanges etc.
This pipe would join two pipe or to a nipple.
This could be directly welded to the run pipe in order to make a branch connection.
• Reducing coupling
It helps to join two different outside diameters of a pipe.
• Reducer insert
These have been manufactured according to MSS SP-79. It helps to enable economic and quick combinations of pipeline reductions. As such, these could be made by using standard socket weld fittings.
Union is a screwed joint design and consist of three pieces which are interconnected. It includes tow internal threads and a centerpiece that would draw the ends together when it is rotated. As such, the unions should be tightly screwed before the ends welded together. This will help to minimize the warping of seats.
Socket weld elbow (SW elbow) has 45 degree and 90 degree types, manufactured in forging processes and also has long radius (LR with 1.5 X OD) and short radius (SR with 1 X 0D) model, it has been a common socket weld fittings that used in the pipelines for changing the fluid directions.
Tee Straight and Reducing Tee
This would help to make a ninety degree branch from the main run of the pipe. Socket weld reducing tee is with a smaller diameter branch which connecting the smaller pipe branch.
Sockolet (sock + olet) is a typical type of socket weld pipe fittings, it is used for the same purposes as weldolet and threadolet, to weld a small diameter pipe to sit in a big diameter pipe body. Different that is sockolet has a unique socket that suitable for the welding (the socket is inside the olet). It provides a good 90 degree turn and higher strength for to take high pressures. One bore connected with the outlet bore, the counter bore will span the OD of the outlet to support the pipe sit on the socket, to stable the installation and welding strength. Same as socket pipe fittings, sockolets have pressure ranges in 3000#, 6000# and 9000#.
Socket weld flange (SW flange) generally used for the smaller pipes with high pressure. The flange shape is consist of a recessed shoulder at the inner bore, which leads the pipe to insert in the shoulder correctly, then do the welding work to connect the pipes and flanges. This welding structural essentially providing a smooth bore and a good transmission performances for the liquid in the pipelines.
SW flanges includes RF (Raised Face), FF (Flat Face) or RTJ face (Ring Tenon Joint) type, pressure ratings classified in 150#, 300#, 600# and up to 2500#.
• The pipe is need to be beveled for preparation of weld
• Temporary tack welding generally no need be required for alignment. This is because the principle in fitting would help to make sure that alignment be proper.
• The socket weld metal is not be able to penetrate the bore of the pipe
• Costs of construction have been found to be lower than butt-welded joints. Due to elimination of special machines and the lack of exact fit-up requirements.
• The welder should make sure that the expansion gap between the shoulder of the socket and the pipe should be 1.6mm
• The internal crevices and expansion gap in socket weld systems would promote corrosion. It would be because of this reason that they have been deemed to be less suitable for radioactive or corrosive applications
• These kinds of fittings would also be unacceptable for UltraHigh Hydrostatic Pressure in food industries. This is because in addition to not allowing full penetration, it would also leave crevices and gaps that would then become very difficult to clean.
Considering above reasons, butt welding is better than socket welding on providing higher strength and higher pressure resistances.
In the case of SW fittings, referred standard is ASME B16.11. Here, a pipe could be inserted in to a recessed area of the fitting. Both the fitting and the pipe shall be square cut and do not require any preparation or beveled end other than cleaning the outside. This will easy the installation and welding processes.
As for butt weld BW fittings, referred standard is ASME B16.9. with their ends being welded on to the pipe end, the thickness would be the same as those of pipes. In this case, the end of the fittings could be beveled.
The socket weld usually resist around half the strength of butt weld fittings. Hence, SW fittings is mainly used for small pipelines with diameters NPS 2 or even smaller.
On the other hand, butt weld fittings helps to keep better strength. And better for high temperature or high pressure pipelines. It also could be used when a welded joint with strength not greater than that of the base metal would be needed.
In case of SW fittings, you will find them to be quite easy to install. Since it requires around 1/6 inches of gap at the bottom of the gap in order to allow the socket access, it also allow thermal expansion. However, this gap could then lead to the problem of over stress which will crack the fillet weld of the fitting. In addition, socket weld has also been found to be problematic in corrosive fluid service as a result of crevice corrosion. Also, it has been found to corrode quite easily due to the discontinuity of smooth pipe internals.
On the other hand, butt weld fittings have been found to be the best in terms of fatigue, strength, compliance with temperature, and resistance to corrosion. However, it could also be more difficult to weld and fit-up properly. Which requires more time and the expertise of skilled welders.
When thinking about using fittings for any construction project, price is a major factor which would need to be taken in to consideration.
Where socket weld fittings are concerned, the price is much higher than butt weld fittings with a similar size. However, the extra cost that associated with butt weld fittings is higher for installation than SW. This is because skilled welder and other labor costs would also need to be factored in.
Hopefully we could be a help for you to attain a better understanding for socket weld and butt weld fittings. If you have any inquiry regarding the SW fittings, just contact us.