July 2024, Vol. 251, No. 7
Features
Circular Economy Initiatives for Offshore Piping and Related Infrastructure
By Feras Alfosail, Qasim Saleem, Mousa Harbi, Saleem Parvez, Rabih Khodr and Khalid Mansour, Consultants, Saudi Aramco, Dhahran, KSA
(P&GJ) — Circular economy is a sustainable business model that aims to ensure use of resources, extraction of maximum value from the equipment during operation and the recovery and regeneration of products and materials at the end of each’s service life.
Conventionally, an early business model of a subsea pipeline was based on a linear model of the design. The concept of circular economy is to provide economic benefits by introducing measures that reduce the effect and waste in early stages of design, reusing and optimizing the equipment performance during its lifetime, then recycling the component and equipment for another application [1].
On that basis, companies and governments are placing more emphasis on sustainability programs and shifting toward minimizing waste, in order to prevent the damage that is affecting the environment [2].
In view of Aramco’s push to achieve net-zero greenhouse gas (GHG) emissions across all assets and operations by 2050, the company has identified interim reduction targets for these emissions that it aims to achieve by year 2035 [3].
To expand on the circular economy, Saudi Aramco rolled-out its strategy by introducing seven principles for circularity which target every phase of the supply chain.
These principles involve initiatives to:
- Design for the circular economy
- Build the circular supply chain
- Reduce environmental impact
- Preserve and extend resources and asset life cycles
- Use regenerative and renewable resources
- Turn waste into resources
- Adapt innovative technologies [4].
Methods
In this section, in order to achieve a sustainable circular economy model, several steps and procedures have been adopted in Saudi Aramco for offshore piping and pipelines under different phases of the model, namely, to reduce, reuse and recycle.
Reduction
First, three concepts and initiatives are introduced: modularization of offshore topside piping, modularization of subsea valves skids and optimization of platform top-side clearances.
The concept for a standardized offshore platform is to “design-one” and “build-many.” The use of standardized structures and skids for subsea valves reduces the amount of resources and materials in construction, which positively affects both cost and schedule.
In order to achieve the maximum, tangible benefits — including the reduction of the carbon footprint — the process focuses on several unconventional areas, such as planning and execution strategy, contracting philosophy, design and technology, material purchase optimization, economics of scale and modular construction. Module sizes and weights are built around rigging and lifting capabilities, load-out and transportation logistics.
This approach helps in achieving multiple cost benefits. For example, long lead equipment can be ordered in bulk — well before a purchase order for a jacket is placed with a contractor. This avoids potential delays, bottlenecks and price escalation during project execution. Transportation of several pieces of equipment at one time also saves on logistical and environmental costs.
Optimizing Piping
In a similar fashion, optimizing the clearances between piping systems on top-side platform piping is essential to reducing the footprint of offshore platforms, thereby reducing environment effects.
As per American Petroleum Institute Recommended Practice API RP 14E [5], which governs the design of piping system on offshore platforms, consideration should be given, during the piping layout planning stage, to providing clearances for maintenance, inspection and operations.
In addition, consideration should be given to account for thermal growth, which affects the piping clearances.
Saudi Aramco has mandated spacing requirements that reduce clearances from the conventional ones used on onshore piping systems, i.e., from 300 mm and 120 mm to 50 mm. In addition, a value engineering study has been conducted to optimize the clearances and spacing to the optimum value, in order to optimize construction costs and schedule.
These areas can be discovered by analyzing the 3-D model, which is validated through construction. It is estimated that optimization will result in a 58% reduction in engineering costs and a 12% reduction in construction costs. A standard production deck module has a fabrication cost that ranges between $9,500 and $11,500 per ton of steel.
Stability
Another area in the early life of the subsea pipeline is the optimization of the on-bottom stability requirement for the flexible pipelines. The design of these flexible pipelines involves using composite materials containing metallic and non-metallic components that meet the requirements of API RP 17J [7].
The circularity in the design phase comes when addressing the lateral stability of the cable to meet international guidelines, which mandate 5D and 10D as acceptable displacement criteria.
Because of the flexural rigidity ratio of the rigid steel pipe to the composite flexible pipe, depending on the cross-sectional properties, the displacement measures can be relaxed to allow the limit of the flexible pipe minimum bend radius to be the limiting factor, instead of the allowable displacement criteria.
Therefore, the displacement of the flexible pipe can be safely set to 20D or 30D depending on soil characteristics. This results in reducing the requirements of the offshore intervention works to install additional concrete mattresses to stabilize the flexible pipeline.
Reuse
Three initiatives are considered in reuse: life extension and integrity management, emergency pipeline repair readiness programs and the reuse of bolted clamps for pipeline repair.
During the lifetime of a given pipeline, it will be subjected to external factors, such as currents and waves, third-party damages and internal factors, such as corrosion and varying operating conditions.
For the purpose of this research, two strategies are considered to improve the life cycle for circularity: a fitness for service assessment program and subsea pipeline free spans optimization.
Due to the corrosion and aging of pipelines, metal loss will take place, requiring quantification. Typically, the condition assessment, based on the in-line inspection (ILI) of a pipeline, is conducted in accordance with its respective code — whether American Petroleum Institute Recommended Practice (API) RP 579 [8], American Society of Mechanical Engineers Design Code (ASME) B31G [9] or Det Norske Veritas recommended practice (DNV) RP F101 [10].
The extension of service life for a subsea pipeline asset can minimize the waste material put into the environment and can also reduce its carbon footprint, by extending its life and minimizing the CO2 emissions from offshore vessels and materials.
The extension of life for the subsea pipeline can be seen in these two steps:
1 - The first step is to consider reduction of the design’s pressure to the maximum pressure during well shut-in conditions for upstream and surge scenarios for downstream.
This reduction will provide leverage in calculating the estimated repair factor and thus keep the remaining wall thickness within the design code of Equation 1 or within the burst condition in Equation 2, without affecting the flow assurance required by production.
Equation 1:
Where P is internal pressure, t is pipe wall thickness, D is pipe diameter, F is design factor and S is the allowable stress based on the yield criteria.
Equation 2:
Where fu is tensile strength, d is depth of corroded area, and l is the length of the corroded area.
In the second step, life extension can be obtained through the ability to perform higher level and more complex assessments, which will provide more leverage and more accuracy, based on burst pressure criteria. These calculations are based on local geometric data of the defects and statistical analysis of the corrosion.
More information is provided in Table 1, which summarizes the strategy conducted for subsea pipeline fitness for service.
A defect that fails to meet the fitness for service criteria will require repair intervention by a mechanical diving team, for a minimum average of 72 hours’ work per location and availability of a repair clamp. Therefore, the application of reduced process parameters resulted in a CO2 emission reduction, associated with diving vessel utilization and material manufacturing.
Optimization
Similar to the fitness for service, free spans correction that is conducted for subsea pipelines and flow lines is quantified. Typically, the condition assessment of a pipeline free span is conducted in accordance with its respective code DNV-RP-F105 [11].
The free span rectification optimization of a subsea pipeline asset can be extremely useful in two ways: it minimizes the waste material sent into the environment, and it reduces the carbon footprint by extending the life of the pipeline and minimizing the CO2 emissions from offshore vessels and used materials.
The number of free spans to be rectified are optimized by, first, considering the global assessment of the pipeline through screening by Equation 3, then, optimized through fatigue assessment of vortex-induced vibration (VIV).
Equation 3:
Where fn is the natural frequency of the pipe in the free span, γ is a screening factor, VR is reduced velocity, Uc,100-year is 100-year return period current flow, Uw,1-year is one-year return period wave current flow and L is the free span length. The term (L/D)/250 becomes insignificant for in-line vibration and is set to zero.
Further optimization can be carried out through subsea pipeline on-bottom roughness analysis. Saudi Aramco introduced an extra step by evaluating the free spans, considering local specific conditions that include metocean, geotechnical and gap data — which suppresses vortex shedding if the gap value is less than three pipe diameters [12]. The schematic (Figure 1) demonstrates ways to optimize the free spans undergoing VIV.
Figure 1: The schematic demonstrates ways to optimize the free spans based on parameters used and type of assessment conducted
As a result of conducting the assessment [13], Saudi Aramco was able to avoid 6,644 hours of diesel engine operation, which eliminated approximately 1255.95 tons of CO2 emissions.
Emergency Readiness
Another area under integrity management is being prepared to respond quickly and effectively in the event of a major incident, resulting in loss of containments has the following benefits:
- Minimizing consequences of failure and reduce repair schedule
- Minimizing waste into the environment by reducing the repair time, thus CO2 emissions from vessels is reduced, and there is less production loss into the sea.
Additionally, Saudi Aramco established repair readiness programs for each field having the following deliverables:
- Establishing a blanket template for each type of repair plan
- Establishing and identifying the required spares for each type of repair plan
- Delivering the repair readiness workshop to field engineers
- Identifying offshore key contractor and services to be developed
More details on the application of the readiness program and use of the risk matrix to identify the repair methodology is available in [14].
The use and reuse of pipeline fittings and piping components from decommissioned pipeline is also addressed. As an example, the use of offshore bolted clamps for subsea pipeline repair is demonstrated. The ability to reuse an existing offshore bolted clamp depends on several factors such as recovery cost, refurbishment requirement and re-installation suitability. Therefore, condition assessment is conducted to verify the ability to reuse the clamp for another pipeline repair location.
Circularity is introduced by minimizing the introduction of waste into the environment. This is accomplished by avoiding the manufacture of new bolted clamps and by resolving the logistical challenges associated by shipping and mobilizing the bolted clamp to offshore fields.
Saudi Aramco installed the first reuse of bolted clamp in 2022 after refurbishment and condition assessment. The clamp size is for NPS 48 pipeline and has a weight of 5.5 tons. The reuse resulted into reducing CO2 emissions by 10.175 tons, not including the reduction in shipping and mobilization cost. [15]
Repurposing
Repurposing of Tires
The recycled of tires to support flexible pipeline, umbilicals and cables is a later step in cutting down on the amount of concrete introduced into the environment.
A typical standard concrete mattress is about 6 meters by 3 meters, with 0.3 meters in thickness. The estimated amount of concrete volume used is 5.4 m3, which contributes to 2,572 pounds (1,166.4 kg) of cement that can produce 1.05 tons of CO2 emission [16]. Figure 2 demonstrates how the tire mattresses are used.
Figure 2: The schematic demonstrate how the tire mattress are installed.
Case Studies
To illustrate these methods, three case studies are demonstrated, based on actual situations from offshore fields in Saudi Aramco.
Case Study 1 – Optimizing Offshore Platform Clearances: To demonstrate circularity in this case, the request was received during the construction and design phase to address the proximity and clearances on several platforms in an offshore field. The value of clearances of piping with structures (Table 2) were reported as follows:
Table 2: Summary of Reported Piping Clearances on an Offshore Platform
The first step was to define the thermal displacement of the piping due to the process parameters. The calculations are based on the stress analysis conducted for the piping system on the platform, which provide the values (Table 3):
Table 3: Summary of Reported Piping Clearances on an Offshore Platform
In addition, the assessment includes verifying the accessibility for maintenance and inspection purposes and ensuring the availability of safe working clearance for personnel.
The analysis of clearances made it clear that modification of these locations would not be required. Offshore construction on each location could have required, on average, as much as 2.637 tons of steel and required 4.88 tons of CO2 emissions from steel mills.
Figure 3 demonstrates the difference between the analysis in the 3-D model and the actual measured clearances in the field.
Figure 3: Clearances showing the comparison between 3-D model (left) and actual in field structure.
Case Study 2 – Subsea Pipeline Fitness for Services:
A subsea pipeline the size of NPS 42 to provide crude oil service is considered in this case study. The design code is ASME B31.8, and the pipeline is made of API 5L X60, with a design factor of 0.72 and an original wall thickness of 25.4 mm. The tensile strength of the pipeline is 5200 MPa.
The design pressure of the pipeline is 15.51 Mpa. After performing the inline inspection, a corrosion defect of 56% loss with a length of 25 mm is found. In the absence of additional corrosion information, the remaining mechanical strength of the pipeline is estimated by applying the level-0 fitness for service using Equation 1.
The remaining thickness t is calculated to be [Equation]. The required pressure for containment becomes [Equation] MPa. It is apparent that the calculated pressure fails the level-0 criteria because it is less than the design pressure.
Before performing any pressure reduction, the Level 1 condition is verified in the burst-pressure criteria using Equation 2, which estimated a burst-pressure value of [Equation]MPa.
Similarly, the estimated burst pressure exceeded the design pressure of 6.267 Mpa, failing to meet the criteria. At this stage, the user either has the option to obtain detailed corrosion mapping of the defect, which is expensive, or perform pressure reduction measures. By conducting flow assurance study to maintain crude oil production and observing the calculated pressure values at both conditions.
In achieving the repair avoidance, a procurement of 4.8 ton of bolted clamp is avoided, which has an equivalent of 8.88 tons of CO2 from steel mills. In addition, an avoidance of 72-hours diving boat for offshore repair works is realized, including seabed preparation, concrete weight coat removal and ultrasonic inspection, eliminating the emissions from diesel combustion engines during the repair campaign.
Case Study 3 – Subsea Pipeline Free Span Correction: The optimization of a subsea pipeline is examined and illustrated as an NPS 20 pipeline with a wall thickness of 15.875 mm and a concrete weight coating of 50.8 mm. A list of free span values is received (Table 4) after conducting the external inspection survey.
Table 4: List of reported free spans during external inspection survey
The reported global values for the maximum allowable free span are 16 meters, 41.97 meters and 27.72 meters for VIV, based on Equation 3, ultimate limit state (ULS) criteria and buckling limits, respectively.
To perform the optimization, the overall diameter is calculated. In order to obtain the height threshold at which the VIV is suppressed. This can be obtained by calculating the gap (height) threshold which has a value of [Equation] mm.
By observation, it is noticed that the free spans reported in Sr. No. 2, 5, 6, 9, 10 and 11 will not require rectification, since the reported height is less than the threshold and will not undergo VIV. Also, the free span values are less than Those reported in the ULS. In addition, a fatigue limit state was conducted considering local metocean and geotechnical data.
The revised VIV limit value corresponding to those locations is 22.4 meters. On that basis, the free spans reported in Sr. No. 1, 3, 7, 8 will not require any rectification.
As a result, out of the list reported in Table 4, only location Sr. No. 4 will require rectification of the free span and the other reported ones will not require any rectification. The waste is minimized by eliminating the CO2 emissions from diesel engines operating during the diving activity, which would require 8 hours per location. For this example, not operating these engines for 72 hours would eliminate 320.6 tons of CO2 emissions.
Conclusion
Circular economy objective strategies and methods are explored in order to achieve a sustainable life cycle in offshore piping engineering. In particular, the methods covered different phases in the life of offshore piping and pipelines, such as modularization and standardization, optimizing piping clearances and optimizing on-bottom stability requirements for flexible pipelines.
Using a reuse strategy, life extension and integrity management are explored, as are an emergency the pipeline repair readiness program and the reuse of existing pipeline fittings.
Also, the use of tire mattresses in pipeline crossing is explored as a method to repurpose the use of materials. Additionally, to illustrate how the methods are applied, three case studies with examples demonstrate how waste is minimized in the process in each category.
The applications of these methods demonstrate how pipeline engineering can help Aramco to achieve its ambition of reaching Net-Zero GHG emissions across wholly-owned operated assets by 2050.
Acknowledgement: The authors would like to Saudi Aramco for their support in developing this work.
References:
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