In this blog, we explained what Oil & Gas flowline and Pipeline are and their differences. Pipeline engineering, Flowline and Pipeline Installation procedures. Also, you are free to contact us for Oil & Gas flowline and Pipeline services.
What is Pipeline engineering?
Pipeline Engineers design, route, plan, and helps in the construction and maintenance of onshore and offshore pipelines. As transporting crude oil, natural gas, refined products, and water through pipelines is the cheapest industrial option available to engineers.
There are many similarities and differences between Pipeline Engineering and other engineering discipline, such as Chemical Engineering, Mechanical Engineering, Civil Engineering, etc.
Read: Flowline, Pipeline & Riser Systems for Operations
Activities like pipeline design and operation, pipeline materials, pipeline integrity management program, pipeline geotechnical engineering, environmental conservation, coatings, corrosion and stress corrosion cracking, cathodic protection, CO2 pipelines are involved in pipeline engineering.
In the oil and gas industry, Flowlines transport fluids between a wellhead and a gathering station like RMS or MSV or treatment facility and vice versa. In a larger well field, multiple flowlines connect individual wells to a manifold. The flow from the manifold is then transferred by a gathering line to a pre-processing stage or to a transportation facility or vessel. Flowlines can run over land or subsea well-field. Flowlines may be buried or at grade on the surface of land or seafloor. The pipelines that collect the flow from multiple flowlines are known as gathering lines.
Flowlines are to a specific well and hence they are located at the well site. It may be a metallic or nonmetallic pipe or a hose. Most flowlines are usually very short. However, they can run for kilometers in onshore applications. Once the flowlines have brought the fluid to manifold or other pieces of process equipment, gathering lines are used. Flowlines are constructed onshore and may be lowered to the seafloor, and have terminal connectors that make an installation at the wellhead easier.
The normal design code followed for flow lines is ASME B31.4 or ASME B31.8
- Temperature and Pressure of Flowlines:
The operating temperature for flowlines is usually less. However, the design pressure is very high. The design pressure can range up to 238 bar. The design temperature of flowlines is normally decided based on the environmental conditions as usually process temperature is low (In the range of 60 Deg C).
Read: Pipeline Design, Construction and Operation Guidelines
The design pressure selected must be more than the maximum pressure that can be produced at any instant of the full flowline life cycle.
- Mechanical Strength:
Depending on the process requirement, flowline sizes vary. The wall thickness of these flowlines is determined using the Barlow formula with a design factor of 0.72. at all locations including road crossings. The Barlow formula assumes a metallic pipe. Carbon steel flowlines are typically installed above ground and this imposes additional bending and thermal (expansion) stresses not taken into account by the Barlow formula. To ensure that code allowable stresses are not exceeded due to these additional stresses on flowlines, support span, expansion loop size & spacing between limit stops, etc should be designed and checked by pipeline stress engineers.
- Flowline Routing:
For laying new flowlines, designated flowline corridors or streets are followed to minimize land use. For these purposes, flowline town maps showing clearly designated flowline routes are developed for each field, and flowlines are planned to follow these routes only. Opportunities for inspectable bulk lines and headers should always be explored.
In planning flowline routes, inspection/maintenance access must be considered. Flowline crossovers wherever required should be provided. The number of road crossings shall be minimized. Space must be maintained for future flowlines. usually, a minimum clearance of 250 mm is required between adjacent flowlines to allow inspection by an external MFL tool. A marker plate to identify the flowline shall be provided every 200 m and at the crossings (before and after the crossing). Welding is not permitted on the coated flowlines.
Read: Compliances for Pipeline System Work in Nigeria
For GRP or Composite pipe flowlines, the following requirements should be considered:
Route Survey
Topographical data
Proximity to occupied buildings.
Location and classes of Wadis, sand dunes, road crossings, types and density of traffic, etc as applicable.
Environmental impact.
The manufacturer recommended a bend radius.
Flowline length optimization.
- Flow-line Materials:
In general, a standard line pipe (API 5L) is used as metallic flowline material. The usual grades that contribute to metallic flowline materials are API 5L Grade B. grade X42, X52, and grade X60.
- Flowline Expansion loops:
Expansion or contraction will occur when the temperature of the flowline material is different from that at the time of installation, or due to pressure and end-cap effects at changes in direction. Suitable expansion loops must be considered while designing flowlines. To prevent preferential expansion in one direction, anchors should be provided to ensure that each expansion loop absorbs only the thrust for which it has been designed.
- Flowline Hook-ups:
Hook-up refers to the piping required to tie-in the flowline to the wellhead and to production facilities. Hook-up piping is designed to ANSI B31.3.
- Flowline Installation:
All flowlines must be properly supported following the pipe support span to maintain less than 15 mm sagging. For flowlines carrying two-phase flow, it’s better to maintain the sagging below 3 mm. So accordingly, the span shall be reduced. Support shall also be provided while crossing existing buried lines.
Read: Pipelines Corrosion Control Standard Requirements
Buried sections of pipelines crossing existing pipelines and other services should be arranged with a ramp or standard road crossing so that access is retained at those services. Where a flowline passes by an electricity pylon, access should be maintained by the use of a ramp or standard road crossing.
To absorb expansion stresses at road crossings, it is recommended that carbon steel lines follow the configuration that allows thermal (expansion) stresses to be channeled into the loops on either side of the crossing rather than into the pipe crossing.
Use of low radius bends at crossings (except when used in a loop configuration) is not advised as the gooseneck formed interferes with inspection and repair.
New flowlines shall be subjected to strength and leak tightness tests after construction. Flowlines are normally hydro-tested at a pressure of 1.25 times the design pressure.
GRP flowlines shall always be buried. Special attention should be paid to supporting and anchoring where GRP is installed on supports in on-plot locations.
- Commissioning of Flowlines:
When the flowline has been successfully hydro-tested, hooked up at both ends, and is ready for operational duty, it is commissioned following specific commissioning procedures.
Read: Pipeline Construction & Maintenance Services
Difference between a Pipeline and Flowline
Both pipelines and flowlines are designed based on ASME B31.4 or B31.8 codes. However, there are some specific differences between a flowline and a pipeline.
All flowlines are part of pipelines. However, the pipelines that run in between a wellhead and RMS or MSV, or treatment facility are termed flowlines.
In a complete pipeline system, pipe flowlines cover a small part of the pipeline system. Hence, the flow line is a special pipeline with its length limited to the oil field area. On the other hand, pipelines run for kilometers and sometimes cross different countries.
Flowlines carry unprocessed crude oil whereas pipelines carry partially processed or fully processed fluids.
Some Definitions
What is a Pipeline?
Pipelines are pipes and other components that transport and distribute fluids that could be natural gas, liquefied natural gas products, crude oil, and other refined petroleum products from one location to another. A pipeline extends from pig trap to pig trap (including the pig traps), or, if no pig trap is fitted, to the first off-take isolation valve within the plant boundaries or a more inward valve if so nominated. Pipelines are designed and constructed following ASME B31.4, ASME B31.8, or ISO 14692 codes. These lines vary in diameter depending on their use, and are generally located underground.
What is a Trunk & Flowline?
Flowlines carry the fluids or gas from the wellhead to and in-between individual vessels in separation, treating, heating, dehydrating, compression, pumping or other processing equipment generally located at or near the well site. The trunk lines are usually the bigger lines. They carry often a lot of oil to the final treatment.
What is a Subsea Flowline?
Pipelines that carry fluids in between a subsea wellhead and a surface facility or manifold are called subsea flowlines. They consist of rigid or flexible pipes and in general, carry untreated oil and gas mixtures.