![]() ![]() ![]() This whole assembly is heat treated after manufacture and then simply welded on the branch of the tee. Another way is to weld a short stub of pipe onto the branch and to design plates that weld into that sub that protrude out into the tee where they act as bars. You may even have to heat treat the tee after welding. That must be done with care to ensure that the welding does not affect the metallurgy of the tee or introduce cracks or imperfections. The simplest and cheapest is to weld bars in there. There are a number of ways of doing this. Barring means that steel bars are welded across the branch of the tee flush with the inside of the pipe to guide the pig through the tee and to prevent it moving into the branch. To prevent that ALL TEE's on a pipeline with a branch size more than say 40% of the pipe diameter are barred. The problem with this tee is that when a pig passing through it it could attempt to travel down the branch and not the straight run, so it could jamb in the tee. Generally the tee is an equal tee however it is also common for the branch to reduce a size or two. The line runs straight through the tee into the barrel, and the fluid is diverted around the barrel through the branch of the tee. Your colleagues may well need the good draining capability twenty years down the track.Įach barrel is attached to the pipeline through a TEE. It is very common for the barrel isolation valves to leak with time. You need those to depressurise the barrel before opening it. This valve is the only barrier you have between the line contents and yourself when the closure is open, and if it leaks you will not only have fluid all over the show, but you may also find it impossible to open or close the closure because you can not get rid of the pressure or the flow.įor the same reason, the barrel must have a good drain valve if it is a liquid system, or a good vent valve if it is a gas system. It must be either a soft seated ball valve or a ball valve with metal to metal seating where the seats are ground and lapped-in to effect excellent sealing. Also, it is very important that this valve have high quality sealing. I am sure all of the valves on your pipeline will be full bore so that pigs can pass unrestricted through the pipeline. That valve MUST be a full bore valve to allow the pig to pass unrestricted into or out of the barrel. The launcher/receiver must have an isolation valve between the barrel and the pipeline. It would be very dangerous indeed to open a closure when their is even a small pressure in the barrel so you MUST have a warning device. This normally takes the form of a small valve that accesses the barrel through the closure which must be open before the closure can be opened. The closure mechanism MUST have a means of ensuring that it can not be opened when their is pressure in the barrel. I personally like the GD closure, most probably the most expensive around. These are expensive pieces of equipment but make opening the barrel an easy task. The barrel must be fitted with a closure and it is normal to install a quick opening closure. Do not use aluminium in the sliding carriage and rammer because aluminium creates sparks when struck on rust. This arrangement will also require a rammer to ram the pig into the mouth of the pipeline so that the carriage can be withdrawn. If your launcher already has a concentric reducer then design a sliding carriage which you can use to locate the pig on the centre-line and slide it down the barrel into the mouth of the pipeline. Also, it sits there at and angle and sometimes jambs. If you use a concentric reducer it is difficult to raise the pig up at the end of the barrel and stick its nose into the line. A pig is easier to launch when the barrel and the pipeline bottoms are on the same level. I would use an eccentric reducer with the flat side on the bottom, at least on the launcher. The reducer between the line and the barrel is not a trivial issue. Find out what pigs you are going to use and make sure the barrel has adequate length. Also, if you are going to use an intelligent pig on this line you will be surprised how long they can be. It is common for the barrel to hold a batch of pigs (say four or six pigs). You can make the barrel diameter smaller, however I would size it so that the flow velocity around the pig is less than 20m/s when flowing gas and 4m/s when flowing liquid. That will ensure that the velocity of the fluid passing around the pig is similar to the flow rate in the pipe when one or more pigs are in the barrel. When the pig is received the fluid has to pass around the pig in the barrel, so it would be a good idea to give the barrel a cross sectional area of about twice that of the linepipe, In your case say 28 inches. The pig must fit loosely in the launcher/receiver so the barrel of the launcher/receiver must have a greater diameter than the pipe itself.
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