SECTION 1: INTRODUCTION The overall design of a pipe pi pe line will be determined by its location, the type of fluid being transported and its operating pressure and temperature. A typical pipeline has many installations which aids its functions as a medium for fluid transport. The following installations will be described, regarding the factors a plant designer would take into consideration.
Pig
traps
Block valves
Offtakes
Compressor
stations.
SECTION 2.1: PIG TRAP Pig
traps are installations used for inserting pigs into a pipeline, then launching, and finally receiving
the pigs at the receiver end .A pig trap is similar to an air lock or torpedo launch tube. They are isolated from the pipeline by a valve so it can be depressurized to load the pig. A pig which stands for pipe intelligence gauge can range from air-filled plastics to magnetic-flux leakage inspection tools.
Once
loaded, the trap door is closed and the trap is pressurized. With the main trap valve
open, fluid can be directed behind the pig to push it into the pipeline. The reverse process applies at the receiver end which is connected to the end of a pipeline in a safe manner. The pig trap when in use is essentially part of the pipeline, and thus , it is important that it is capable of withstanding the pipeline conditions such as pressure, temperature and the effects of the service medium , i.e. Corrosion.
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2.1.1 DESIGN Pig
traps are pressure vessels, and like other pressure vessels, should be capable of retaining
pressure whilst allowing tools to be launched and received.
This determines the overall trap
dimensions. Tools such as pigs are long and heavy and must be considered, along with the internal pressure requirements. Typical basic design parameters to be considered include design code, design pressure, design temperature, materials, external loadings and cyclic requirements. DESIGN CODE
This should be of national or international standards such as ASME
B31.4, B31.3, B31.8, PD5500,
EN13445, and AS2885. Since they are attached directly to the end of a pipeline as an isolatable extension, traps can often be designed to a vessel code rather than a pipeline code. This provides a significant challenge in meeting the pipeline internal diameter with a thicker calculated vessel wall. In this case a specification break between the pipeline and trap. In other cases, the trap can be designed to the same code as the connecting pipeline. Whichever approach is selected must ensure all appropriate loadings and conditions are addressed to produce a safe working design. DESIGN PRESSURE
The design pressure must be known in order to determine the wall thickness of the vessel. The design pressure should never be less than the pipeline pressure. The design pressure can be clientspecific or based on the ASME/ANSI pressure/temperature class tables. Upon completion, each vessel should be subjected to a hydro- static test pressure at least 1. 25 times the design pressure. The actual test pressure is generally dictated within the chosen code. Some codes allow for the vessel to be pneumatically tested in lieu of hydrostatic testing. However, due to the risk associated with the use of air gas, special precautions must be taken. TEMPERATURE
Temperature would take account of the maximum design temperature, but also the minimum design temperature for material selection.
2
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In order to print this document from Scribd, you'll first need to download it. Often specified by the clients, however where possible it is better to allow the trap manufacturer to select materials that are compatible with the pipeline materials and meet the design specification Cancelthat theDownload And Print requirements. This approach ensures most suitable, cost effective and readily available materials that fully meet the design requirements are selected. It is important that line products are specified (whether it is sour, toxic, or corrosive). This will influence not only the metallic elements, but also the elastomeric materials, which typically constitute the closure-sealing element. Finally any material selected must be compatible with its mating material in respect of weld ability, wall thickness, chemical and mechanical properties. MATERIALS
EXTERNAL LOADINGS
These loads consist of those imposed by attaching pipe work acting upon nozzles. In addition, external pressure due to water depth in subsea application could fall into this category. CYCLICAL REQUIREMENTS
If the unit is subjected to frequent pigging operations, this may in turn create sufficient cyclical loading warrant fatigue analysis. In addition, support loads, wind blast and seismic loadings and loads induced during transportation of units should be considered. 2.1.2 LAYOUTS
In addition to mechanical and process considerations, the trap designer must also consider practical issues such as location, environment and logistics. For subsea applications, the trap should include additional protection for the valves and pipe work in form of protection frame to reduce the risk of damage clashing with fishnets or ship anchors. For unmanned, hazardous, or frequent pigging operations, multiple launching capabilities should be considered. Pig
traps must be located away from ignition sources and must also have sufficient space to open
the door without infringing the space of the operator and allow the tools to be loaded and unloaded safely. The layout must ensure that all valves are accessible from either the ground level or via permanent platforms or ladder and that operation of any valve does not require the operator to enter the closure door opening envelop. The operation of the valve must where possible be from the side opposite the door hinge. Units should be located so that they are oriented with their end closures pointing away from personnel areas and critical items of equipment to minimize the risk of damage which might occur in the unlikely event of a pig being ejected from the trap under pressure. Dip
trays and bunding must be installed to prevent contamination due to service medium.
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of a pipeline is generally undertaken in a manner that a voids any adverse effect on the
environment and incompliance with applicable health and safety regulations and procedures. Manufacturers instructions should be followed for operation of pig traps. Major operations include: preparation (valve arrangements), sending pigs, receiving pigs, and tracking(including pig speed calculations).
2.1.4 MAINTENANCE
Routine and scheduled maintenance is essential for optimum performance of the pig trap. Inspection should form part of the maintenance regime relating the conditions of components to inspection and maintenance in the future.
2.2 BLOCK VALVES Controlling
the fluid travelling through the pipe and equipment, and accessibility to the controlling
apparatus are one the two major concerns in any piping facility.
Block
valves are used for
interrupting the flow or to shut in a section of the pipeline. A block valve is normally either fully open or fully closed. This is why gate valves are preferable. The block valve is a major component in the control valve manifold. With these valves the operator can isolate any segment of the line for maintenance work or isolate any rupture or leak.
Fig 2. Gate valve
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The advantages of gate valves over other stop valves are y
Negligible hydraulic resistance when the passage is open fully
y
No reversal of the flow of working medium
y
Possibility
of use for highly viscous medium.
The block valve design are classified in terms of various features linked with operating conditions; chemical compositions, temperature and other parameters of working medium, level of operating pressure, type of drive and material from which the body is made of. The mechanical considerations for design of block valves are y
Resistance to weathering
y
Leak-tightness
y
Resistance to bending between supports
y
Should meet seismic standards
of seat and packing
2.2.2 OPERATION
The block valve should be able to block flow in both directions. Three methods of controlling block valves can be considered; locally, remotely, and automatically. The appropriate method will be determined from likely effects of a leak and acceptable release volumes, based on the total time in which a leak can be detected, located and isolated. The closure time of the valve should not create unacceptably high surge pressures. 2.2.3 LAYOUT Locations
of block valves to control pipeline spills can be optimized for controllability, maintenance,
and spill control. For onshore pipelines, the spacing for sectionalizing block valves should consider limiting the pipeline liquid contents between adjacent valves. The different types of block valves include; Manual gate valves which are locally operated valves and are placed in the check valve sections from time to time in other to ensure positive isolation, Remote gate valves which are used to protect sections of oil and gas pipelines in the event of a serious failure or break in the pipeline and Station block valve located both in the inlet or fluid suction side and outlet or fluid discharge side to separate the pipeline from the pump station in case of an emergency. 2.2.4 MAINTENANCE
In order to maintain the block valve properly, the operator will need to implement a scheduled routine of sealant system top-ups with synthetic lubricants. Typically, a new valve will require top-up more often than a valve that has been in operation for one year or more. It is the first critical year of 5
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2.3 OFFTAKES A
Distribution
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network receives from the transmission system at the offtakes which contain
instrumentation telemetry equipment for filtration, pressure management, measurement and odourization to enable remote monitoring and control of gas flows. An offtake can be a pipeline transporting fluid from a larger pipeline or a vessel transporting fluid from one point to another.
Fig 3. Offtake station 2.3.1 DESIGN Pipeline
offtakes should be designed so as not to reduce the strength of the pipeline system. A
pipeline is generally characterized by its internal and external diameters, type of material and fabrication, and its length. The flow of fluid through a pipeline is function of its internal diameter, the length, the pressure at the end points, and the elevation of the profile of the pipeline, the flowing temperature and physical characteristics of the fluid. Gas removed from the network at offtakes must meet a minimum pressure requirement. Some major issues the designer should consider are; y
The maximum operating pressure
y
The maximum operating temperature
y
The wall thickness of the header
y
The commodity been transported
y
The tie-in status(cold tie-in, or hot tie-in)
y
The available options(unreinforced stub-in, reinforced stub-in, tee, weld-o-let, split tee)
2.3.2 OPERATION AND LAYOUT Offtakes
must be designed to incorporate compression stations with adequate and well designed
branching with the mainline. The control of activities of an offtake station should be done by high capacity computers with real-time capability pro-efficient monitoring and analysis. Most pipeline operating companies employ a sophisticated and versatile programme called supervisory control and data acquisition (S CADA) for their pipeline operational planning and surveillance.
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In orderthrough to print this Scribd, you'll Gas pressure drops as it travels the document pipeline. Cfrom ompressor stations are located throughout to download it. preventing the gas from dropping to dangerously the network to maintain first flowneed at high pressures, low pressures. 2.3.3MAITENANCE
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When maintaining the offtakes, restrictions to flow of fluid such as debris should be cleared to prevent pressure dropping to dangerously.
2.4 COMPRESSOR STATION A compressor station is an installation on the transmission system that uses gas turbines to boost pressure in the pipeline system. It is used to increase transmission capacity and gives natural gas moving through the pipes the required force to move it to the next booster station. These stations add enough energy to the gas to overcome frictional losses and maintain required delivery pressure and flow rate.
Fig 4. Compressor station 2.4.1 DESIGN AND LAYOUT
The following should be considered in designing a compression station 7
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Control
systems for compressor stations exist at four levels;
Cancel driverDownload Print unit control, auxiliary system supervisory control, station level control, and driven And equipment level control. SAFETY SYSTEMS: Several safety systems exist, including relief valves, fire and gas detection units.
The basic piping layout of a compressor station consists of y
A scrubber to prevent liquids from entering the compressor
y
A blow relief and blow down valve
y
A by-pass line
y
Gas coolers to reduces the discharge temperatures
The overall design of a compressor station is dependent on y
The type, size and configuration of the drivers and compressor
y
Climatic
y
Location
y
Regulatory, environmental and safety requirements
y
Proximity
Compressor
conditions, including temperature, humidity and air borne contaminants relative to support resources to inhabited area
units may be configured in series or parallel or a combination of both.
2.4.2 OPERATION
Most of the operation of compressor stations is automatic with only minimal intervention of human operators. However, equipment manufacturer instructions should be strictly adhered to for optimum performance. The operators of the system continuously monitor and adjust the mix of compressors that are running to maximize efficiency as well as keeping detailed operating data on each compressor station. The control centre can also remotely operate shut-off valves along the pipeline system. Advisably, delicate hardware called emergency shutdown (ES D) controller is required to control valve sequencing and respond to fire and gas detection. However, the main controller has the capability for outages due to failures or maintenance. To ensure safe operation, the compressor station is continuously monitored. There are three types of shut down and conditions warranting them. UNIT SHUTDOWN RESTARTABLE (USR): This is indicative of process conditions problem and caused
by; I.
High suction and/ or discharge temperature
II.
Low
suction pressure
III.
Low
speed
IV.
High discharge pressure
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Lube
first need to download it. system failure
II.
High vibration
III.
High bearing temperatureCancel
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EMERGENCY SHUT DOWN: When human safety is jeopardized and its caused by
I. II. III.
Fire and gas detection Customer
emergency shutdown(ES D) signal
Seal system failure and value misalignment
2.4.3 MAINTENANCE
It is a common practice to have a system of routine, intermediate and major maintenance or overhaul. This prolongs the life of equipment and hence the compressor station. Maintenance of a compressor station can be considered under the following BUILDINGS AND GROUND : Included in this is the general maintenance and cleaning of buildings and
clearing of buildings and environment. PIPING AND VALVES : Piping at compressor requires little maintenance and is thus easy to ignore. GAS COOLERS: Most of the problems associated with gas coolers can be detected with vibration
sensors and therefore many coolers are installed with vibration monitors that have one sensor for each fan. SAFETY EQUIPMENT: A critical part of maintenance is the variety of safety related equipment that
exists. These consist of fire extinguishers, fire and gas detection systems, special protective equipment, and first-aid supplies. TANKS:
One
of the most pervasive problems of liquid petroleum storage tanks is build-up of solids
and sludge; hence they need to be clean regularly. ENGINE COMPRESSOR CLEANING: The major cause of deterioration in gas turbine performance is
fouling of engine compressor blades. Regular cleaning with recommended fluid isessential.
SECTION 3 CONCLUSIONS Pipeline
installations enhance the general operation of a pipeline, helping in cleaning the pipeline,
blocking flow of fluid during emergencies, diverting flow of fluid, and boosting the fluid pressure. The design considerations concerning layouts, design and operation, and maintenance of these installations are very vital for smooth operation of the pipeline.
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Picture
of a compressor station.
Picture
of an offtake route
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Picture
of pig trap
Picture
of block valve on pipeline
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REFERENCES
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1)
Kadir
02(2010) university A, transmission lecture note: GEMDownload of Salford Cancel And Print
2)
www.Pipelineandgastechnology.com. Accessed on 21-10-10
3)
www.Springerlink.com. Accessed on 2-11-10
4) www.Virtualpipelinespaces.live.com. Accessed on 2-11-10 5)
www.Intellisitesuite.com . Accessed on 3-11-10
6)
www.Wikipedia.org/wiki/compressor_station. Accessed on 5-11-10
7)
www.google.com. Accessed on 5-11-10
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