Engineering Challenges Facing Oil and Gas Pipeline Projects

By V.K. KHANNA, Engineering Consultant, Gurugram, India 

(P&GJ) — Pipelines for oil and gas products are the lifeline of the energy sector. They carry crude oil and other industry liquids from storage to processing units, as well as carry finished liquid and gases to the users. During their construction and operation, these pipelines encounter various terrains and geographical stretches, such as river or ravine crossings, lakes, different types of soil, waterlogged or marshy areas, liquefiable soil stretches, hills, slopes, seabed portions and so on. In addition, there are also direct and indirect natural hazards to consider. There are many engineering challenges faced during pipeline project execution and operation periods. This article covers those critical engineering aspects relating to pre-construction and during construction, encompassing those that are most critical.

Cross country pipeline projects face a variety of hazards—both natural and induced.1 These eventualities and constructional requirements are predicted at the project formulation stage. The basic design, front end engineering and bid documents contain essential engineering information, with field checks included in the scope of contractor duties. Engineering challenges likely to be encountered on the project are predicted before start of work and identified during execution in the field. This article touches on these challenges and introduces engineering aspects involved—particularly the most critical of these, as well as those requiring a special technical approach. The latter require an expert test check and resolution, without going into comprehensive and structured components. This article is aimed at consolidating engineering information, for the benefit of project implementation and operational periods.

ENGINEERING CHALLENGES NEEDING DISCRETE ATTENTION

Route survey. A route survey is undertaken to determine the optimal route of a pipeline and to formulate the project and its scope. Its accuracy will determine the success of a project in terms of time and economics, without any deterrents. The use of special instruments, like laser instruments, viewfinders, GPS/DGPS, preliminary soil testing kits, water toxicity kits (for likelihood of corrosion), side-scan sonar and magnetometer (for offshore), will help during route survey. Thus, once the route survey is reliably carried out, a detailed survey and soil or other investigations can go ahead smoothly.

Investigations. Geotechnical investigation includes recommendations for various factors, including:

• Safe soil-pipeline interaction
• Soil resistivity
• Waterlogged regions (for variation in water levels to ascertain buoyancy)
• Likely hazards (for flooding and seismicity)—both natural and manmade
• Soils subject to liquefaction
• Hydrological and bed data for rivers majorly in spate
• The extent of water toxicity for a sea/harbor area
• Wave pattern and bed depth variation
• Vacuum excavation (potholing), to locate and confirm the position of existing utility lines to prevent damage.

Basic design package. The basic design package should be firm and cover all aspects of design, based on data as near to reality as possible, with no room for alteration during implementation of the project.

Bid document. The bid document should be complete with investigation data and/or parameters as near to reality as possible, even if the contractor is directed to verify the field data before every stage.

In addition, both the basic design package and bid document should be reinforced by an interactive session with bidders, who should either agree to the bid information or justify alteration.

CRITICAL ENGINEERING ASPECTS

Geohazards. These include potential hazards like landslides or seismic activity, to ensure the route is safe and pipeline can withstand these conditions.2

Geophysical methods:
Techniques like seismic-refraction or ground penetrating radar (GPR) can provide subsurface information without direct sampling, helping to map soil layers and identify anomalies.

Stability assessments identify unstable soil conditions, such as those prone to slides or creeping, which could cause costly remedial work and pipeline damage.

Stress relief and monitoring involve geotechnical data that can inform the placement of sensors for strain monitoring, allowing for the detection of potential issues and timely intervention.

Pipeline under buoyancy. The designers suggest adding negative buoyancy using methods like concrete weight coating, concrete saddle weights or deeper burial to keep the pipeline stable and in place. The weights shall be designed to keep the pipeline always at designed depth even under varying water depths and to be able to counter the flow velocity during flood ingress or receding. If required anchoring by shallow piling can also be carried out.

Pipelines buried in soil that can liquefy: Straight pipelines. This scenario is a very critical situation. Under the influence of seismic load and surge, the pipeline is likely to be affected by ground settlement or buoyancy and lateral movement. If the surge is high, with simultaneous seismicity and the soil is being liquefied, the overall effect is difficult to ascertain. Under the additional effect of stresses developed by the pulsating surge wave, the pipeline may even be deformed. It can also be subject to 3D movement, and in the case that the pipeline crosses a seismic faultline, failure could happen. A lot of research on this aspect has been done based on various modelling data, such as the “seismic-excitation and soil-pipe” system.

Pipeline bends. The author has carried out a study of buried pipeline bend under the simultaneous influence of surge, seismic load and marshy soil (susceptible to liquefaction). The analysis was carried out using the finite element method (FEM). A finite element model of a quarter pipeline bend was developed to capture these combined effects. The result of this model establishes that bends are vulnerable to localized overstressing at the soil-pipeline interface, while the surrounding soil layers dissipate stresses effectively. These findings suggest that design measures, such as flexible joints, additional reinforcement or better ground improvement around bends, may be required to mitigate differential displacement and ensure long term structural integrity. These provide clear guidance for operators and designers and highlight the need for targeted reinforcement of bends and soil support measures in multi-hazard environments.

It may be stated here that surge-induced pressure rise is estimated using the Joukowsky relation: ΔP = ρ a ΔV, where ΔP is the pressure rise (MPa), ρ is the fluid density (kg/m³), a is the acoustic wave speed in the fluid (m/s)—modified as needed, to account for pipe wall elasticity—and ΔV is the instantaneous change in fluid velocity (m/s) from valve closure or compressor trip.

PIPELINE BURIED IN PORE WATER-BEARING SOIL

In the situation of pore water-bearing soil, laying pipeline is difficult, and it becomes necessary to dewater the soil. Dewatering can be done using open-pit pumping. In the case that the trench does not become dry, dewatering can also be done using the wellpoint method. In this method, small diameter pipes, with holes to allow water to trickle in, are pushed into the ground in a row on either side of the trench, clear of the pipeline diameter. All the well point tubes are connected by a header, leading to a vacuum pump. The pump draws the water from well point tubes to create a dry trench to lay the pipe.

Pipeline bend where pipeline rises from underground to aboveground support. A pipeline transition from underground to aboveground support under seismic and surge loading is challenging, as soil-structure interaction, uplift, enhanced stresses and the dynamic effects of ground movement against pipeline make the system complex to analyze and interpret. In such a scenario, the use of flexible connections—strategically located supports to absorb energy and prevent failure during the combined forces of earthquake and internal surge pressure—may help mitigate the hazard.

Pipeline bend where pipeline rises from under the sea to above trestle-bridge support. This configuration poses a challenge for pipeline design—particularly at the bend—as both oil and gas pipelines are affected by internal fluid forces, such as surge and vibration, wave action and trestle-bridge movement-induced forces. Oil pipelines are subjected to kinetic energy and consequent impact loads from fluid, while gas pipelines face challenges from negative pressure at high points. It may be noted that the weight of the pipeline and the fluid, together with the forces generated by movement or drift of trestle bridge, load the system in more than one direction, and so care is required to design the system properly. Anchoring the pipeline with well-designed support is also important.

Pipeline stringing under seawater to lay on seabed. Pipeline stringing on the seabed is a specialist job, carried out by companies experienced in the work. Methods like S-lay, J-lay or reel-lay are adopted. Factors to be kept in mind include operating conditions, current, waves, seismicity, on-bottom stability, stability against current, free span analysis for unevenness of seabed, coating and cathodic protection for safe design in executing the job.

Directional drilling under rivers/crossings. Horizontal directional drilling (HDD) is a trenchless construction method for installing belowground pipelines, by drilling a precise, curved path from a surface-mounted rig. It is used where the open cut method is not usable. The process involves three main steps: visualizing the creation of a pilot bore along the chosen path, reaming the bore to enlarge it to the required parameter and pulling the product pipe through the widened tunnel.

Trestle bridge in sea/harbor: Checking foundation piles’ strength under varying lengths. Pipeline from Jetty or single buoy mooring (SBM) that rises from the seabed to a trestle bridge customarily has its foundations on piles. These piles are embedded to the seabed. However, the seabed is not stable, and the silting and erosion of bed soil are regular phenomena. Checking the pile strength and lateral deflection with varying seabed levels is done via special software visualization, such as RSPile or S-FOUNDATION, which can model changing pile length, soil properties and axial/lateral loads. Pile safety, with respect to regular seabed phenomena, is a critical aspect of pipeline projects and requires discrete care.

FIG. 1. Conceptual schematic illustrating the combined action of surge-induced internal pressure, seismic excitation and soil-pipeline interaction on a buried pipeline bend in soft or liquifiable soil. The figure highlights the concentration of stresses and deformation demand at bends under multi-hazard conditions, emphasizing the need for special design and analysis beyond single-hazard assumptions.

Takeaway

The article covers the major sensitive and critical engineering aspects when it comes to oil and gas pipeline projects. These nuances related to engineering aspects have been highlighted for the benefit of readers and professionals. The buried pipeline bend analysis under combined forces, namely surge, seismic and soil pressure under marshy (liquefaction) conditions has been carried out, using FEM as a practical approach. However, experimental set up may also be needed to compare the results. The interaction of surge pressure, seismic excitation, and soil deformation at pipeline bends is schematically summarized in FIG. 1, reinforcing the vulnerability of such locations under multi-hazard conditions. Other takeaways include:

• Pipe bends in marshy or soft soils are the most vulnerable points under surge and seismic loads
• Soil pressure peaks at the pipe-soil contact zone but dissipates outward into the surrounding soil
• Reinforcement of bends and improvement of soil support can significantly reduce risk
• FE modeling is a practical tool to predict high-stress zones and guide cost-effective mitigation
• Bends at underground to aboveground transitions and bends transitioning from undersea to trestle-bridge are vulnerable points and require care
• Piles for trestle-bridges require special checks.

_{LITERATURE CITED}

1. _{ISO, “13623:2017, Petroleum and natural gas industries—Pipeline transportation systems,” 2017}

2. _{ISO, “20074:2019, Petroleum and natural gas industry—Pipeline transportation systems—Geological hazards and risk management for onshore,” 2019}

3. _{Cui, Y., O’Rourke, T.D., and Jeon, S.S. “Seismic response of buried pipelines subjected to ground deformation,” Journal of Geotechnical and Geoenvironmental Engineering, 2006}

4. _{ABS, “Subsea Pipeline Systems,” 2006}

5. _{DNV, “DNV-OS-F101, Submarine pipeline systems,” 2021}

6. _{ASCE, “MOP 108, Pipeline Design for Installation by Directional Drilling (Second Edition),” 2014}

About the Author

VIJAY KHANNA has 26 yrs of experience in the oil and gas sector while working with Engineers India Ltd. (EIL) until March 2001. He also has 50 yrs of experience with engineering projects, working on the Engineering Review for the Jumbo LPG I plant for Sonatrach in Algeria. Khanna also served as the project engineer manager for the first hydrocracker plant in India, as well as the project manager for a grassroots refinery at Numaligarh, the BPCL refinery expansion at Mumbai and for several revamps. He has been published in leading international industry publications, including Hydrocarbon Processing in 2001, H2Tech in 2023 and 2025. Khanna has earned a BS degree in chemical engineering and a PGD in management.