Pipelines provide the most economical and efficient means of conveying fluid over long distances. In the oil and gas sector, pipelines are used to convey liquid and gaseous hydrocarbon from various facilities as may be required.
Due to the difficult terrains encountered along the pipeline route, pipeline construction is difficult. An accurately selected pipeline route significantly reduces the effort required to design and construct the pipeline.
This article is aimed at explaining pipeline routing for onshore pipelines. The routing discussed is in conjunction with the survey and soil investigation performed to firm up the pipeline route. Factors to be considered during pipeline routing will be discussed. Though the routing considerations stated here are mainly for an onshore pipeline, some offshore or water bodies considerations are fused into the article
Figure 1: Ongoing Pipeline Construction on a ROW
Pipelines may traverse a few kilometres, a hundred or thousands of kilometres. In the case of short pipelines, routing is easy; however, as pipelines become longer, pipeline routing becomes more difficult.
A pipeline may be entirely onshore, offshore or both. Pipelines may be designed to be installed above ground or below ground. The installation state also greatly influences the selection of the pipeline route.
Various obstacles may be encountered between a pipeline’s start and endpoint. These obstacles include roads, railways, water bodies, bad soil conditions, and utilities. The above-listed parameters greatly influence the pipeline route.
Pipeline routing is performed to determine the optimal route from the pipeline’s start to the endpoint.
Pipeline routing is a key activity performed during the design stage of a pipeline. It is performed across all the design stages including Conceptual stage, Front end engineering design and detailed engineering design. In some cases, minor changes may be made during the construction stage. The changes during construction may result from uncaptured obstacles and information during route surveys and soil investigations.
Pipeline routing considerations include:
Establish the shortest possible route. Shorter route results in a reduced cost of material and construction. Short route may also eliminate the need for intermediate pumping or compression station but this may not entirely be true if there are numerous obstacles along the route.
Minimize roads, rail and water bodies crossing.
Minimize the number of bends. Bends angle should be limited to maximum 90 degrees. The bend radius should satisfy the requirements of codes and standards such as ASME B31.4 and 31.8.
Avoid inhabited areas as much as possible.
Utilize existing pipeline right of way as much as possible. Utilizing other utility infrastructures and cables ROW should be considered. Interference between cables and pipelines should be properly investigated before the decision of parallel routing is taken.
Minimize environmental impacts by avoiding protected areas, cultural resources etc.
Avoid areas with side hills.
Access from the existing road to the ROW is key for transporting construction equipment and pipeline materials..
3 Developing A pipeline Route
Route development takes several stages; the development of the route is performed on a desktop by marking on maps which may be available in the public domain. One of the key software used for preliminary route development is google earth. It provides satellite imagery and a street view of the earth which is utilised for pipeline routing. Other more advanced software’s utilised include ArcGis and QGis. Offshore pipeline preliminary routings may be developed using a combination of google earth maps and admiralty charts. Note the charts used should be the latest version to show all facilities and infrastructures within the pipeline route. As the route is developed, it is refined until the final route is approved. Also, note that the final route must have gone through several approval stages from local to federal government depending on the Country’s regulations.
Figure 2: Cropped Out section of an Admiralty Chart
The admiralty charts provide details of water body’s depth, the location of obstacles such as existing pipelines and cables, and the location of facilities such as seaports, anchoring zones etc.
Below are the steps to be taken to develop a pipeline route. Note these steps may vary due to design requirements or local regulations.
3.1 Identify the Connecting Facilities
A pipeline must connect at least two facilities, e.g. a fuel storage facility and an export or import terminal, a crude processing facility and a refinery, a wellhead and a flow station, a gas processing facility and gas distribution facility etc.
The first step is locating these facilities appropriately on a map or GIS software. For new facilities, location selection is not solely the responsibility of a pipeline engineer but a joint task performed by all departments (process, piping, mechanical and pipeline). The client should be well briefed on selecting the respective facilities. The coordinates of these locations are noted.
3.2 Develop Preliminary Routes on Maps
After identifying the facilities, preliminary routes are developed. While developing a pipeline route, developing more than one option may be required, which is further analysed to determine the best. In some instances, Company’s best option presented to the government for approval is never approved. An already-developed alternative route is then presented.
Developing a preliminary pipeline route is mostly performed using google earth software.
Google Earth seems to be the most effective tool for preliminary pipeline routing. It uses satellite imagery that is periodically updated, thus providing reliable information. Existing pipeline and powerline right-of-way scars can be easily seen on Google Earth satellite imagery because the scars from construction or maintenance are evident. Roads, rails, rivers and other water bodies are also easily identified.
The engineer gradually and carefully identify paths that are predominantly free from obstacles, i.e., from buildings, crossings, etc. This is done by carefully placing marks along the map and using a line to connect the marks. Note the coordinates of the marks are noted as they are placed along the route.
A pipeline should be routed to avoid cemeteries, reserved forests and lands housing sacred objects.
Below is a preliminary route drawn on google earth for illustration. The route connects a proposed power plant to an existing terminal gas station. The various turning points along the route are aimed at minimising pipeline proximity to existing facilities.
Figure 3: Preliminary Route Drawn on Google Earth
3.3 Identify Obstacles along the Routes
After the preliminary routes are developed, all obstacles are properly noted and documented. In addition to marking the obstacles on the route, a detailed list of all obstacles with their description is developed. The obstacle list should include details such as:
The name of the obstacle, e.g. road crossing, river crossing, railway crossing, pipeline crossing.
The centre point coordinate of the obstacle.
Description of the obstacle this may include information such as dual carriageway, major river.
The start coordinate of the obstacle, i.e. start point of the road or river crossing.
The end coordinate of the obstacle.
The total length of the obstacle, i.e. total river crossing length, total road crossing length.
The state, local government and community the obstacle is located
3.4 Identify and Review Pipeline Impact on Communities
The community should be consulted during the planning stage of the pipeline because the pipeline has a significant impact on the community. Pipeline and Community safety should be reviewed, and the route updated to accommodate all recommendations. Safety of the pipeline is key; close community interaction with the pipeline may lead to pipeline vandalisation.
The land is also critical to the community; therefore, the ease of land acquisition from the community and other organisations should be factored into the pipeline route.
3.5 Select the Most Feasible Route for Survey
In this sense, the preliminary most feasible route does not refer to the route with the lowest construction cost. In selecting the most feasible route, the pipeline’s safety and constructability are key factors. The pipeline’s impact on the environment and other factors should be considered. The most feasible route is thus presented to the government to seek a survey permit.
3.6 Develop the Pipeline Route Utilising Appropriate Scale
After the preliminary route is marked out on maps or appropriate software, the route is further presented on a standard back sheet with an appropriate scale.
The route may be developed on A1 or A2 paper with an appropriate scale depending on the length of the pipeline. Typical drawing scale used includes 1:50,000, 1:100,000 etc
3.7 Obtain a Permit to Survey from Government
Obtaining a permit to survey is very important because the pipeline route developed is through lands owned by individuals, organisations, etc.; therefore, the appropriate government authority must grant a permit. The developed route is submitted with the application for the permit to survey. After reviewing the route and the application, the government may grant a permit to survey or reject it. The government may give reasons for rejection, and alternate routes may be developed and resubmitted.
A granted permit permits the holder, together with his workers and equipment, to enter any route specified to perform activities such as:
Survey and take levels of the land along the proposed route;
Dig and bore into the soil and subsoil;
Cut and remove trees, vegetation and other objects that may impede the survey activities
Perform all acts necessary to ascertain the suitability of the proposed route for the planned pipeline.
While trying to access the proposed route, access through a third-party facility may be required; therefore, the permit also grants the holder the right to access these third-party facilities. Before any land or third-party facility is accessed, discussion and notification shall be served accordingly to all parties, in some cases a minimum of 14 days.
3.8 Carry Out Pipeline Route Survey
A route survey is the most critical activity performed in the technical execution of pipeline routing. It is only performed after the preliminary route has been developed. Most of the alterations to the preliminary route result from a detailed survey performed. Before acquiring a ROW, the route must be surveyed and deemed okay for the pipeline construction.
Below are major surveys performed to firm up a pipeline route.
Figure 4: Pipeline Route Survey Works
3.8.1 Pipeline Centreline Survey
A pipeline centreline survey is performed to verify the preliminary desktop-developed route. It is performed to confirm the suitability of the route for pipeline construction.
During this activity, the surveyor performs a reconnaissance survey of the entire route, utilising equipment such as a global positioning system (GPS), theodolite, magnetic compass, inclinometer etc. While inclinometers estimate the slope along and across the pipeline route, theodolite, GPS and magnetic compass are used to estimate positions on the pipeline route.
During this survey, the route is established on the ground, restrictive areas are identified, and detours to the preliminary route are established and firmed up. While performing this operation, developmental plans and information required for obtaining clearance for the pipeline are obtained.
The surveyor establishes stakes and flag control points on the ground at key locations along the proposed pipeline centreline, rivers, canal, major roads, rail, terminal stations etc. these stakes and control points are also necessary if the Client desires to verify the activity performed by the survey physically.
At the end of this survey, the route is updated on topographical maps, ground profile showing elevation along the route is developed. Also, a report shall be developed showing details including:
Ground profile along the route
Bathymetric feature for water bodies
Land use pattern
Site location suitable for pipe storage
Soil strata along the route
Features such as forest reserves
A bathymetric survey shall be performed for offshore pipelines as part of the centreline and detailed route survey to determine the depth of water and map out features of water bodies
3.8.2 Detailed Route Survey
In some cases, a detailed route survey may be performed separately to supplement the centreline survey, while it may be performed in conjunction with the centreline survey. The detailed survey covers a minimum of the envisaged right of way (ROW). Some of the detailed information to obtain if not done during the centreline survey include:
Reconfirm the pipeline alignment on the ground
Obtain all topographical features within to beyond the envisaged right of way
Finalise crossing angles and locations
Obtain ground levels and contours
Obtain details of land use
Reconfirm or establish stakes at all turning points/intersection points (TP/IP)
3.8.3 Cadastral Survey
Along the proposed pipeline route, a cadastral survey is performed to establish land ownership boundaries, land ownership status, restriction and interest in the designated land.
This survey is used to plan for ROW of acquisition, dispute settlement etc.
The cadastral survey shows all the information on land ownership and status obtained from relevant government agencies or persons. At the end of this survey, maps showing physical delineation are developed, and a detailed report covering the entire proposed route is developed.
3.8.4 Soil Investigation Survey
A soil investigation survey is performed to obtain the physical and geotechnical properties of the soil along the pipeline route for engineering design and construction planning. Soil investigation activities performed include
Obtaining disturbed samples from boreholes
Visual engineering classification of soil along the proposed pipeline route
Perform standard penetration test at a specific location
Laboratory testing of the collected soil samples to determine engineering properties
Usually, boreholes are drilled at an identified location, usually around 250m apart, except:
At the intermediate point where a change in soil type is observed
For streams, river crossings and canals, boreholes shall be drilled on both banks and one on the bed of the water body.
At least one borehole shall be made at railroad and highways.
The samples obtained from boreholes are tested to determine properties including:
Type of the soil up to the boring depth
Soil bulk and dry density
Natural moisture content
Water table level
For clayey soil; Un-drained shear strength
Soil angle of internal friction
3.8.5 Location Classification Survey (Applicable to Gas Pipeline)
A location class survey is performed to determine the level of development along the pipeline route. The development is a function of the number of building intended for human occupancy.
Location classes are defined in ASME B31.8 section 840.2.1.
To determine the number of buildings intended for human occupancy for an onshore pipeline:
Lay out a 0.4km wide zone along the pipeline route with the pipeline on the centreline of the zone.
Divide the pipeline into random sections 1.6 km in length.
Note that each dwelling unit in a building is considered a separate building intended for human occupancy.
Four location classes are defined in ASME B31.8, which are location classes 1, 2, 3 or 4.
Location Class 1: Any 1mile (1.6km) section that has 10 or fewer buildings intended for human occupancy
Location Class 2: Any 1mile (1.6km) section that has more than 10 but fewer than 46 buildings intended for human occupancy
Location Class 3: any 1mile (1.6km) section that has 46 or more buildings intended for human occupancy except when a Location Class 4 prevails
Location Class 4: Areas where multi-storey buildings are prevalent, where there is heavy or dense traffic, and where there may be numerous other utilities underground
Note: The higher the location class, the lower the design factor (F); this results in a higher wall thickness, thereby increasing pipeline safety. See ASME B31.8 Table 841.1.6-1 and Table 841.1.6-2 for design factors corresponding to the various location classes.
3.9 Review the Routes and Reroute Accordingly
If required, the developed route is refined utilising the survey results. Based on the survey results, detours to sections of the route may be proposed resurveyed and implemented. The detours may result from avoiding unstable soil, hilly grounds, cemeteries, religious centres, forest reserves, rivers etc.
The refined route developed on a proper back sheet is further used to obtain final approval to construct the pipeline.
3.10 Seek Government Approval
Seeking government approval implies obtaining a permit to construct the pipeline. All documentation, including the surveyed route, is collated and submitted to the government to grant the construction of the pipeline
ASME 31.8: Gas Transmission and Distribution Piping Systems
Code of Federal Regulations 49 (CFR 49), Part 192
Oil Pipelines Act Chapter 338; Laws of the Federation of Nigeria 1990
DPR P-1P: Guidelines and Procedures for the Design, Construction, Operation and Maintenance of Oil and Gas Pipeline Systems in Nigeria