Sunday, July 29, 2012
Various Activities Involved In Various Phases of Pipeline Project Implementation and Pipeline Designs Features
Posted by Ankit Chugh on 11:11 PM
Pipeline is the most preferred option to transport oil, gas or products in bulk. It could be thousands of km long, branched and networked.
Configuration of both oil & gas pipeline are very similar. A cross country oil or gas pipeline system, normally starts with pumping of oil or compression of gas to develop the requisite pressure to travel a long distance. The pressure required for pumping of oil or compression of gas depends on pipeline length, pipe diameter, & destination pressure requirements. For long pipelines (hundreds of km), booster compressor for gas pipeline and booster pumps for oil pipeline are required along the length.
Gas or oil (or any other liquid being transported) is transported along the length to many customers. Normally the following processing facilities are required upstream at the oilfield, which has been described earlier:
· Separation of oil, condensate and free water
· Compression of gas, if necessary to deliver at required pressure at shore
· Pumping of oil
· Dehydration of gas to protect the pipeline from corrosion
· Sweetening, if necessary, to remove H2S.
Configuration of Cross Country Pipeline
A typical cross country pipeline system starting from an offshore field has the following facilities along its route as shown in figure.
· An offshore platform where the oil or gas is produced.
· PLEM near the platform (Pipeline End Manifold) from where the pipeline starts (or a Dispatch Terminal on land).
· An SPM (Single Point Mooring) connection the subsea pipeline to a tanker, if oil is transferred from a tanker instead of platform.
· Pig launcher.
· Subsea pipeline reaching shore at what is called Landfall Point.
· A Receiving Terminal at the landfall point. It has equipment like pig receiver, filter, storage for oil, pumping for gas, processing of gas, compression and dehydration. The description of the various equipment is given in later part of this unit.
From the receiving terminal oil & gas is sent through cross country pipeline, which could be hundreds of kilometers in length to several customers along the route. There could be several customers along the routes like power stations, fertilizer plants or other industries.
For distribution to each customer, there will be a Distribution Terminal having filter, meter etc.
Normally, there are booster stations with booster compressors for gas and booster pumps for oil after every few hundred kilometers to compensate for the pressure loss in the pipeline.
The entire facility is monitored and managed to SCADA system. SCADA is a central monitoring system, which monitors the entire pipeline parameters over several hundred kilometers by tele-metry and tele-control.
Normally, LPG and petrochemical feedstock like ethane/propane are taken out before giving the gas to the industrial consumer. The bulk of the remaining gas is mainly methane (above 90% by volume).
Like any other project, a cross country pipeline project too passes through various phases of implementation from feasibility study of design, construction and operation as shown in following figure. But like any other industry, there are certain special aspects that need to be taken care of in a pipeline project.
Safety and reliability in design and construction is important as pipeline carries a huge reservoir of explosive substance through environmentally sensitive areas.
Also since access is required on the land through which the pipeline passes, legalities involved in getting Right of Way (ROW) is a very important.
Some of these aspects will be discussed in this section.
· The maximum planned throughput and turn-down
· The characteristics of the fluids to be transported
· The pressure and temperature requirements
· The mode of operation
· The geographic location and the environmental conditions.
In order to determine the possible range of operational parameters of the pipeline, a hydraulic analysis should be performed.
For a given pipe size, fluid properties and flow rate, the hydraulic analysis should provide the pressure and temperature profiles all along the pipeline for steady state and transient conditions.
Full account should be taken of possible changes in flow rates and operational modes, over the complete operational life of the pipeline.
Thy hydraulic analysis should provide information on: surge pressure during shut-down of a liquid line, turn-down limitations and inhibition or insulation requirements to prevent wax or hydrates deposition, effect of flow conditions on the efficiency of corrosion inhibitors, liquid hold-up and slug control requirements at the downstream end of two phase lines.
The most important end results of design are:
· Material of pipeline
· Diameter of the pipeline
· Wall thickness
The selection of the pipeline material type is a fundamental issue to be decided at the conceptual design stage of a pipeline project. The most frequently used pipeline materials are carbon steel. When the fluid is corrosive, due to presence of hydrogen sulfide, carbon dioxide, or oxygen, special steel is used. The potential long-term impact of corrosion has to be considered during design and it can be demonstrated that the pipeline can remain fit-for-purpose throughout its lifetime.
The diameter depends on:
· Available pressure drop i.e. the difference between starting pressure (P1) and desired delivery pressure (P2)
· Actual pressure drop depends on design flow rate (Q) selected and friction factor
· Static head adds up to pressure differential in case of liquids
· Actual pressure drop should be less than available pressure drop