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Pig Traps Offtakes Block Valves Engineering Essay

A pipeline system is a transportation network of pipes, valves, and other parts connected together to deliver gaseous or liquid products from a source (supplier) to a final destination, usually a customer. Examples of products transported through pipelines are water, sewage, natural gas, gasoline, and crude oil. Most pipelines are buried underground, but occasionally a portion of a pipeline system may be installed aboveground.

The finished design of a pipe line will be ambitious by its locale, the kind of fluid being transported and its working pressure and temperature. A normal pipeline has countless installations that aid its purposes as a medium for fluid transport. The listed installations will be delineated, considering the factors a plant designer should seize into consideration, which includes:

Pig traps

Offtakes

Block valves

Compressor stations

Each of these, installations are going to be discussed based on their main features concerning the layout, design and operation and maintenance of the system.

PIG TRAPS

Pig traps furnish a way of loading and unloading pipeline tools, as well as intelligent pigs into pipelines. They seize the form of a vessel that can use diverted flow for whichever dispatching or receiving. The vessel can be remote from the pipeline to enable the loading and unloading of pipeline tools. As the trap (when in use) is a vital part of the pipeline, it is vital that it is capable of tolerating the pipeline conditions such as pressure, temperature, and resistance, and the effects of the fluids. The figure below is a cross sectional diagram of a pig launcher. (1)

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Figure 1: pig launcher and pig receiver (Courtesy: Piping Guide)

DESIGN AND OPERATION

Pig traps have to be projected to match the pipeline section design specifications. The mechanical design characteristics of the pig trap should encounter or exceed the design pressure, have the alike design factor, have compatible physical kind, be projected employing the same design code and be suitable for the same temperature scope as the pipeline section that it serves. Also, a pig trap has to be dimensionally suited for the kind of pigging that is anticipated on the pipeline section. The critical lengths of the barrels and line size pipe section have to be long enough to accommodate the most extended pig that will be utilized in the pipeline section. When selecting where to find a pig trap, there are several things to consider. The pig trap ought to not be allocated adjacent each open flames or combustion sources. Countless constructing codes and pipeline firms have laws and regulations concerning what kind of power equipment are allowed inside precise distances of an opening to the pipeline such as a closure door. If the pig trap is to be placed in a span where horizontal space is not at a premium (such as on an offshore platform or a refinery), then care ought to be taken to give adequate work space adjacent to the closure door for pigging operations. These procedures can take the form of loading and unloading long inspections pigs, removal of liquids and debris from the pipeline and into a rubbish container, installation and procedure of a provisional separator, etc. Another thought that is vital to the harmless and effectual operation of a pig trap is how the barrel is oriented at the pigging station. Each valves or instrumentation associated alongside the operation of the pig trap ought to be given adequate space to provide routine maintenance or replacement. The closure door should face away from the other equipment and places where people normally congregate (i.e. break areas, parking lots, etc.). There have been scarce occurrences where pigs have shot out of pig traps and broken equipment, as well as, injured people. The oversized pipe section of a pig trap is not named barrel by coincidence. (2)

Design codes

Pig traps and pigging arrangements ought to be designed according to the same design codes as the pipeline to that they are connect-ed. The predominant codes utilized for pipe-line design in countless states are composed by ASME. The ASME codes usually encountered in the pipeline industry are ASME B31.4 which laws the design of fluid pipelines; ASME B31.8 that laws the design of gas pipelines; ASME B31.3 that laws the design of procedure piping and ASME Serving VIII, Div. 1 and 2 that laws the design of pressure vessels (sometimes denoted to as the Boiler Code). There are supplementary codes in use that govern the design of pig traps such as CSA Z-662 in Canada or ASME B31.11 for slurry pipelines.

It is helpful to the purchaser of pipeline equipment to comprehend a little of the contrasts amid the usually utilized ASME codes. ASME B31.4 – Pipeline Transportation Systems for Fluid Hydrocarbons and Supplementary Liquids (crude oil, fluid petroleum gas, anhydrous ammonia, alcohols and carbon dioxide) allows for design alongside precise steel materials – ASTM A694 F42 to F70, A707 L3 CL3, A105, A350 LF2, A182 F316, A182 F51 (Duplex) and others. (3) or (4)

LAYOUT

This involves the siting of pig trap systems and the possible adverse environmental results that could upshot during construction and operation. Pig traps should also be sited so that the end closures of the pig launcher/receiver are pointing away from personnel areas and critical items of equipment. This will minimize any damage emerging from the unlikely event of a pig being ejected from the trap whilst under pressure.

MAINTENANCE

Routine and projected maintenance is vital for optimum presentation of the pig trap. Inspection ought to form a portion of the maintenance administration associating the conditions of constituents to examination and maintenance in the future.

BLOCK VALVE

When we say valves, they are devices that control the movement of fluid within a medium. So narrowing it down to block valve which is also known as gate valve is a device that restricts or minimizes fluid flow in a pipeline. The main feature of a gate valve is the sealing surfaces between the gate and seats are planar, so they are frequently used during a straight-line fluid flow or minimal fluid flow is occurring. In the petroleum industry, the gate valve is most desired due to its ability the pierce through the liquid. Below is a cross sectioned diagram of a gate valve.

http://www.tpub.com/content/doe/h1018v2/img/h1018v2_29_1.jpg

Figure 2: a simple gate valve (source: marine insight)

DESIGN, LAYOUT AND OPERATION OF A VALVE

The actual construction/design of gate valves, for example, could vary extensively reliant on its application, the materials utilized, or the manufacturer’s own distinct features. The working principle, though, will be the same. Valves can be specially made to work at high or low temperatures (cryogenic), or to extremely elevated standards for use in explosive atmospheres, or after no leakage is permissible.

Characteristics

Sealing systems and materials: All valves are prone to leakage as it is tough to attain a flawless seal, even though the use of distinct seal materials can have extremely good consequence If high protection is needed, use can be made of two valves in sequence, one being the main valve and the subsequent as a back-up ought to the early failure. Some valves have bleed holes installed to notice leakage across the seal. If two valves are utilized jointly, a bleed hole could be fitted in the pipe in between that can be opened after the valves are closed to drain each leakage. (Block and Bleed valves)

Housing materials: An expansive scope of materials is utilized in valve production, the particular material rely mainly on the fluids to be handled. Iron and steel are generally utilized for oil/petroleum uses alongside most valves being made of mild or alloy steel. Brass valves are utilized for water (as well as cast iron, steel and supplementary alloys)

Motion of valves: Many tinier valves are operated by hand if they are accessible. Larger valves need power actuators and inaccessible valves of all kinds need a little form of mechanical or electrical actuator. Pneumatic (compressed air) and hydraulic cylinders and mechanisms are extensively utilized in larger applications. Tinier valves can work alongside solenoids, but larger valves need extra convoluted motors and mechanisms for electric powered operations.

They are many standards to which you can design valves which include the British Standards (BS); American Petroleum Institution (API); US standards ANSI; Imperial/Metric Systems. (5)

So care must be taken that valves are compact and leakages can occur.

During the operation of this valve, the following points should be considered:

Direction of the flow

Direction of the opening and closing

Finally, the lever

Valves ought to be always opened and closed slowly, except in emergencies. Quick closing can cause pressure waves to craft up and move back across the system, perhaps provoking harsh damage, erupt or injuries. This phenomenon is recognized as “water hammer” in internal water system and a loud knocking sound can be heard in the pipe.

LAYOUT

Locations of block valves to manage pipeline spills can be optimized for domination, maintenance, and leak control. For onshore pipelines, the spacing for sectioning block valves ought to ponder manipulating the pipeline fluid contents amid adjacent valves. The disparate kinds of block valves include; Manual gate valves that are innately worked valves and are allocated in the check valve servings from period to period in supplementary to safeguard affirmative isolation, Remote gate valves that are utilized to protect servings of oil and gas pipelines in the event of a weighty wreck or break in the pipeline and Station block valve placed both in the inlet or fluid suction side and outlet or fluid discharge side to distinct the pipeline from the impel station in case of an emergency. (6)

MAINTENANCE

Periodic maintenance consists of inspecting the stem for leakage and tightening the gland nut as required. Keep the threaded stem oiled to prevent rusting and clean up any dirt or sand which adheres to the stem. Cycle the valve (if possible) to keep the valve from seizing in one position. Keep paint away from the stem Threads, as it can build-up and increase torque and may keep the valve from seating properly. (7)

COMPRESSOR STATION

Compressor Station simply means a facility that improves the movement of natural gases (CNG) from one place, which is transported to a pipeline system. The movement of gas occurs in a pipeline, it is necessary for the end user to receive the gas at a certain pressure which needs to be constant, and this is achieve from the help of distinct turbines and engines. When install a compressor station, the size of station and amount of compressor varies, due to the volume of gas being transported, and the diameter of the pipe. The essential parts that make up a compressor station are the liquid separator and prime movers. Liquid separator remove liquid and particles before it goes through the compressor station and the prime movers drives the compressors. Below is a diagram of a typical compressor station as it performs its duty in the oil and gas industry.

http://www.askchesapeake.com/PublishingImages/ask-pipelines-gastransportation-448x291.jpg

Figure 4: Pipelines transportation to end users. (Courtesy: U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration)

DESIGN AND LAYOUT

When designing a compressor station, from the layout there are certain things an engineer should put in consideration to achieve maximum performance, and the following are, thus: safety measures, impact to the environment and the economics of the operation and the materials used to design the stations.

When we take about material selection, it is dependent on achieving the requirements in conjunction to the wanted performance, both economically and mechanically, and also we must consider the life span of the machine.

When we say safety measures, which also have an effect to the environment as a whole, we take about trying to handle the leakages of the gases and spillages.

The overall design of a compressor station thus depends type and size of compressor used, temperature reactions to the equipment should be considered, and the location of the equipment.

OPERATION

The operation of this equipment is involve in two parts, unit control and station control, both due to advancement of technology and research, we now use what we call, digital technology which handles both operations. The unit control comprises of microprocessors which controls the turbine compressor body to run a flow / pressure points from the direction of the operator. This control monitors the compressor’s operation to ensure that it will not trend into surge. If the operation tends to the surge line, the unit control activates a safe recycle valve for maintaining smooth operation. The station control also inhabits and monitors that of the unit control and gives the interface between the operators and the plant. This provision is in form of video or print data, recording important parameters. (8)

MAINTENANCE

Monitoring and scheduling flow of vibration, temperatures, and other critical operational values by the compressor Programmable Logic Controller unit identify service needs to prevent massive and dangerous equipment failures. Maintenance systems should be developed to manage all maintenances prior to station startup and running. All underground pipe and structures are to be coated with a corrosion protective and electrically insulating coating. Additionally, steel pipe installed belowground is protected from external corrosion using cathode protection. Equipment should be standardized as feasible to reduce spare parts requirements. Good human factor conducts should be utilize in evaluating access to and viewing of operating data, manipulation of controls, installation of isolation devices, and removal and replacement of equipment. (8)

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