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Pump Truck Manifold Overview
The pump truck manifold is the series of valving and piping that allows control of the pressurized fluid from the triplex pump on a pump truck. I will be focusing primarily on the service rig pump truck for now.
There seems to be three primary styles when selecting a pump truck manifold: threaded, welded and integral systems. There are some pros and cons of each system which I will discuss below. For general knowledge, these manifolds are designed for 5000psi maximum, 500gpm maximum and standard service.
The threaded manifold is exactly as it sounds. It uses national pipe thread (NPT) to connect the joints of the piping together to make a pressure seal. This is by far the simplest way to build a manifold. Threads can be cut using a standalone pipe threader, or machined and assembled in place. A threaded manifold requires no special certifications or quality control regulations (unlike a welded manifold) and can be built by a less-skilled operator.
Some care does need to be taken with NPT threads. They will need to be turned to just the right amount of engagement before they will hold pressure. It can be difficult to get a pressure seal and have the components orientated correctly. Operation-wise you do run the risk of the pipe backing off and not holding pressure over time. From a design point-of-view, you also usually need a heavier wall pipe when threading. The wall thickness calculations also require consideration of the thread depth. This could result in a much heavier manifold then other options. The preferred valve is a gate valve because of their simplicity, ability to throttle flow, and resistance to wear. The simplicity of this system also lends itself to sour service if required by simply changing the material properties of the components used.
Welded manifolds have been growing in popularity recently because of the uniformed and light weight of the finished product. Welded manifolds generally use no NPT threads and combine the use of hammer unions and welded connections to form the manifold. Although in many cases, a hybrid can be used that has some threaded fittings on components like check valves and pressure gauges. This solution can simplify construction. The use of welding allows you to remove the bulky overlapping fittings required on NPT connections making for a lighter and more compact manifold. There are also no threads being cut into the pipe so the entire wall thickness can be used for structural purposes allowing you to run a smaller schedule of pipe. The manifold also stays connected for the life of the unit since there are no threaded joints, nothing that can come loose or be adjusted.
The preferred valve in this style of the manifold is the same as the threaded version except with a butt-welded body. The difficulty of welding these manifolds revolves around the quality control and procedures in the manufacturing. Now that you are welding pipe with pressure in it, the manufacture is required to make sure they have qualified weld procedures for each of the materials and use a qualified welder to do the work. A good portion of the welding is done from branched tees so the pipe can’t be rolled to keep the weld position simple. The hammer unions (which are usually 4130) and the main valve bodies can be uncommon materials and have particular weld procedures that require specific and different post-weld heat treatments. Once all these procedures are in place, the actual construction should be straight-forward but the leg work to get set up is substantial. The cost of this manifold is higher than that of a threaded unit and slightly less than the integral version.
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The integral manifold is a manifold made-up of individual joints of piping, usually forged, with a hammer union on each end. The manifold is constructed by chaining together as many of these individual joints up as required. Each joint is certified to a specific pressure and since there is no modifications done to the actual components during assembly, all of the certifications and quality control is on the piping supplier’s side. I am a big fan of this style of manifold since changing it or replacing worn out components is as easy as disconnecting the hammer unions. Achieving a 5000psi to 15,000psi manifold or one that is sour service rated is just a matter of selecting the correct components. Designing this system is easy. Other sections of the oil industry (such as fracing) have already made the leap to doing their piping in this way. I believe it is the way of the future. The downside of the integral manifold is that it is expensive and heavy. It also looks complex because of all the hammer union joints. The integral manifolds come with a plug valve instead of a gate which is a less preferred valve style and I have heard conflicting reports on how they perform in the field.
The Future of Manifolds
I roughly touched on three different styles of manifold design and discussed the different applications of each. I personally think the future lies in the integral manifolds but I would be interested in a discussion on the topic.
What manifolds are you running and what is your opinion on the future of manifolds?
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