Interview Questions for Pigging Procedure Development

Pipeline pigs are devices used to clean, inspect, or maintain pipelines. They come in various types, each designed for a specific task. Think of them as specialized cleaning crews for pipelines.

• Cleaning Pigs: These are the most common type, used to remove debris, liquids, and other unwanted materials from pipelines. They can be scraper pigs (removing deposits), foam pigs (for cleaning lighter materials), or gauze pigs (absorbing liquids). For example, a scraper pig might be used after a pipeline maintenance project to remove any leftover metal particles.
• Inspection Pigs: These sophisticated pigs carry instruments that measure the pipeline’s internal condition. Magnetic Flux Leakage (MFL) pigs detect metal loss, while ultrasonic pigs identify wall thickness variations. Imagine them as pipeline doctors, diagnosing problems before they become major issues.
• Batching Pigs: These pigs separate different products within a pipeline, preventing mixing. This is crucial in multi-product pipelines, ensuring the integrity and quality of each substance. Think of them as diligent traffic controllers in a pipeline.
• Smart Pigs (Intelligent Pigging): These sophisticated pigs combine cleaning and inspection capabilities, integrating sensors for data acquisition and often wireless communication. They provide detailed, real-time pipeline data to improve efficiency and safety, helping operators quickly assess problems.

Developing a pigging procedure for a new pipeline is a crucial step, requiring detailed planning and consideration of various factors. It’s like creating a comprehensive instruction manual for the pipeline’s cleaning and maintenance crew.

1. Pipeline Data Gathering: Collect comprehensive data on the pipeline’s diameter, length, material, bends, and fittings. This information dictates pig selection and operational parameters.
2. Pig Selection: Choose the appropriate pig type(s) based on the pipeline’s purpose, the types of materials to be removed, and the inspection requirements. Factors such as fluid viscosity, temperature, and pressure play a critical role here.
3. Procedure Development: Define the pigging sequence (launch, travel, reception), including pressure and velocity limits, as well as monitoring points. This procedure must address all phases of the operation, from setup to completion, including emergency scenarios.
4. Risk Assessment: Identify potential hazards and implement mitigation strategies. This includes emergency shut-down procedures, personnel safety, and environmental protection measures.
5. Testing and Review: Test the procedure using simulations or small-scale trials before full-scale implementation. Conduct thorough reviews and modifications before finalizing the document.
6. Documentation: The procedure should be documented clearly and unambiguously, including diagrams and safety procedures, ensuring every individual involved understands the process.

Selecting the right pig size and type is vital for efficient and safe operation. An improperly sized pig can damage the pipeline or become stuck, leading to costly downtime.

The selection process involves:

• Pipeline Diameter: The pig must have a diameter slightly smaller than the internal diameter of the pipeline to allow for smooth passage. Tolerances must be carefully considered.
• Pipeline Geometry: Bends, valves, and fittings dictate the pig’s design and shape to prevent damage and ensure successful passage. Special pigs, like those with flexible bodies, might be needed for complex pipelines.
• Pigging Fluid Properties: The viscosity and pressure of the fluid being pigged will affect the pig’s design and speed. For example, a high-viscosity fluid might require a higher-pressure pigging system.
• Pigging Objective: The intended purpose (cleaning, inspection) influences pig selection. A simple cleaning pig is different from a sophisticated smart pig with multiple sensors.

Calculations are often performed using specialized software to determine the ideal pig size and ensure safe operational parameters are met.

Safety is paramount in pigging operations. A failure to address safety concerns can lead to serious accidents or environmental damage. Think of it as the foundation upon which the whole operation is built.

• Pre-Pigging Inspection: Thorough inspection of the pipeline and pigging equipment is crucial to identify any potential hazards before initiating the operation.
• Emergency Shutdown Procedures: Clear and easily accessible emergency procedures are essential in case of unexpected events, such as pig sticking or leaks. Regular drills and training improve readiness and response time.
• Personal Protective Equipment (PPE): Appropriate PPE, including safety glasses, hard hats, and hearing protection, must be used by all personnel involved in the operation.
• Confined Space Entry Procedures: If access to the pipeline or pigging equipment requires entry into a confined space, strict confined space entry procedures must be followed.
• Environmental Protection: Measures must be in place to prevent environmental damage, such as accidental spills or leaks. Containment and emergency response plans should be in place.
• Competent Personnel: All personnel involved in the pigging operation must be adequately trained and competent in the procedures and safety regulations.

Pre-pigging and post-pigging inspections are vital for ensuring the safety and efficiency of the operation. They act as quality control checkpoints before and after the ‘cleaning crew’ has done its job.

• Pre-Pigging Inspection: This involves checking the pipeline’s integrity, ensuring there are no obstructions that could impede the pig’s passage. It also includes inspecting the pig itself for any damage or defects.
• Post-Pigging Inspection: This involves inspecting the received pig for damage or debris collected, which can provide valuable insights into the pipeline’s condition. A visual inspection of the pig’s exterior and analysis of any collected materials are often performed.

These inspections not only prevent potential incidents but also provide valuable information about the pipeline’s condition, allowing for timely maintenance and repairs.

Managing risks associated with pigging operations requires a proactive and systematic approach. This involves identifying potential hazards and implementing controls to mitigate their impact.

• Hazard Identification and Risk Assessment: A comprehensive risk assessment is conducted to identify all potential hazards, including pig sticking, pipeline damage, and environmental contamination.
• Mitigation Strategies: Appropriate mitigation strategies are implemented to reduce the likelihood and impact of each identified hazard. This might include using specialized pigs, implementing stricter operating procedures, or providing additional training to personnel.
• Emergency Response Plan: A detailed emergency response plan should be developed to address unforeseen events, such as pig sticking or pipeline leaks. This plan should outline the steps to be taken in the event of an emergency, including emergency shut-down procedures and notification protocols.
• Regular Training and Drills: Regular training and drills are essential to ensure that personnel are familiar with the procedures and emergency response plans. This improves their preparedness and response time in case of an emergency.
• Data Monitoring and Analysis: Data from pigging operations should be routinely monitored and analyzed to identify trends and areas for improvement. This information can be used to refine procedures, improve safety measures, and reduce the likelihood of future incidents.

Pigging systems have evolved significantly, with intelligent pigging leading the way. This is no longer just a simple cleaning operation, but often a highly sophisticated data collection process.

• Conventional Pigging: This involves using simple cleaning or batching pigs, often relying on manual pressure control and visual inspection. It’s the simplest but also least informative method.
• Smart Pigging (Intelligent Pigging): This utilizes sophisticated pigs equipped with various sensors that gather real-time data about the pipeline’s internal condition. Data on wall thickness, corrosion, and defects can provide crucial information for pipeline integrity management. Different sensor technologies include MFL, ultrasonic, and caliper tools, enabling detailed internal assessments.
• Pipeline Inspection Gauge (PIG): A form of smart pigging. This system uses different types of tools, including those that measure wall thickness, detect internal defects, and assess the condition of coatings.
• Automated Pigging Systems: These systems automate various aspects of pigging operations, including launch and reception, pressure control, and data monitoring. These systems increase efficiency, safety, and data consistency.

Troubleshooting pigging operations requires a systematic approach. It starts with identifying the specific problem. Is the pig stuck? Is the pipeline pressure unexpectedly high or low? Is the pigging time longer than expected? Once the issue is defined, we can move to diagnostics.

• Stuck Pig: This could be due to several reasons, including pipeline geometry issues (bends, restrictions), pig design flaws (incorrect size or type for the pipeline), or debris build-up. We’d check pipeline integrity using pipeline inspection gauges (PIGs) to locate the obstruction. We might then use different pig types—such as a bypass pig to clear the blockage or a foam pig to help propel the main pig.

• Pressure Anomalies: High pressure might indicate a blockage, while low pressure suggests leakage or a problem with the pumping system. We’d use pressure transducers to monitor pressure changes along the pipeline and use this data to pinpoint the location of the issue. This data will help determine if the pig is damaged.

• Extended Pigging Time: This usually points to frictional issues, such as pipeline roughness or pig deformation. We would examine the pig for damage and evaluate the pipeline condition using data from previous pig runs and pipeline inspection tools.

The key is to use a combination of real-time data monitoring and historical data analysis to understand the root cause and implement the appropriate corrective action. Often, we use simulation software to model different scenarios and test potential solutions before implementing them in the field.

Pigging failures stem from various sources, broadly categorized into:

• Pipeline Issues: These include pipeline obstructions (debris, corrosion, internal build-up), changes in pipeline diameter or geometry (unexpected bends, welds), and internal pipeline damage.

• Pig Design and Selection: Choosing the wrong pig type for the pipeline diameter, fluid viscosity, or flow rate is a common culprit. Incorrect pig size or material selection can lead to damage or failure. For example, using a polyurethane pig in a pipeline prone to high temperatures would lead to pig degradation.

• Operational Errors: These could be mistakes in pig launching or receiving procedures, incorrect pressure settings, or inadequate monitoring of the pigging operation. Improper training or lack of attention to detail can easily lead to operational errors.

• Equipment Malfunction: Problems with the pumping system, pressure monitoring equipment, or the pig launcher and receiver can all contribute to pigging failures. Routine maintenance and inspection is crucial to avoid these issues.

Understanding these potential failure modes allows for preventative measures like thorough pipeline inspections before pigging, proper pig selection based on pipeline characteristics, and rigorous training and supervision of personnel involved in the operation.

Data logging and analysis are crucial for optimizing pigging operations, ensuring safety, and preventing future failures. It allows for real-time monitoring of key parameters such as pressure, flow rate, pig speed, and temperature. This data is invaluable for:

• Real-time monitoring and control: Identifying potential issues early, enabling timely intervention and preventing major failures. For instance, a sudden pressure drop could signal a pipeline leak.

• Optimization of pigging parameters: Analyzing data from past runs allows for adjusting parameters like pressure and flow rate to improve efficiency, reduce pigging time, and minimize wear on equipment.

• Pipeline integrity assessment: Identifying potential problems such as corrosion, blockages, or changes in pipeline geometry, contributing to predictive maintenance strategies.

• Compliance and reporting: Ensuring adherence to regulatory requirements and providing detailed documentation for audits or incident investigations. Data logs serve as a crucial record for regulatory compliance.

Software tools for data analysis and visualization greatly aid in interpreting this information and extract actionable insights.

Ensuring accurate pigging data relies on a multi-faceted approach:

• Calibration and Verification: Regular calibration of all measurement instruments (pressure transducers, flow meters, temperature sensors) is essential. Verification checks against known standards ensure accuracy.

• Data Validation: Implementing checks and balances to identify and correct erroneous data points. Automated data checks can help catch outliers or inconsistencies.

• Redundancy: Employing multiple sensors or measurement systems to provide redundant data streams. In case of sensor failure, we have backup data to rely on.

• Data Logging System Integrity: Using reliable and robust data acquisition systems capable of handling large amounts of data and minimizing data loss or corruption.

• Data Analysis Expertise: Employing trained personnel to analyze data and interpret the results accurately. This requires understanding both the data acquisition and the physical process of pigging.

Accuracy also comes down to choosing the right equipment for the job and understanding its limitations. For example, certain pressure gauges are best suited for certain pressure ranges and should be chosen accordingly.

(Note: Regulatory requirements vary significantly by region. The following is a general overview and should not be considered legal advice. Always consult local regulations.)

Regulatory requirements for pigging operations often cover aspects of safety, environmental protection, and operational integrity. These might include:

• Pipeline Safety Regulations: Regulations governing pipeline design, construction, operation, and maintenance, including specific requirements for pigging operations.

• Environmental Protection Regulations: Regulations relating to the handling and disposal of any fluids or materials released during pigging operations. This includes regulations on spill prevention and response.

• Operator Training and Certification: Requirements for personnel involved in pigging operations to receive proper training and hold appropriate certifications.

• Record-Keeping and Reporting: Mandated reporting procedures and record-keeping practices for pigging operations, including detailed documentation of all activities.

• Emergency Response Plans: Plans outlining procedures to follow in the event of a pigging-related incident or emergency.

It’s crucial to stay updated on the latest regulatory changes and ensure compliance throughout the entire pigging process.

Calculating the required pigging pressure is complex and depends on several factors. A simplified approach is often used, but a more accurate calculation requires specialized software and may involve Computational Fluid Dynamics (CFD) modeling.

In a simplified approach, the pressure required is determined by:

• Friction Losses: Resistance to flow along the pipeline due to friction, which depends on the pipeline’s roughness, diameter, and fluid viscosity.

• Elevation Changes: Pressure changes due to variations in pipeline elevation. Pumping uphill requires higher pressure.

• Pig Geometry and Size: The pig’s size, shape, and material affect the pressure needed to propel it through the pipeline. Larger pigs generally require more pressure.

• Desired Pig Speed: The speed at which the pig needs to move to effectively clean the pipeline impacts pressure requirements.

The formula is complex and often expressed as:

Where:

• ΔP = Pressure drop
• f = Darcy friction factor
• L = Pipeline length
• D = Pipeline diameter
• ρ = Fluid density
• V = Fluid velocity
• g = Acceleration due to gravity
• h = Elevation change

This is a simplified representation, and the actual calculation often involves iterative procedures and corrections for various pipeline conditions. Specialized software is usually employed for accurate results.

My experience encompasses a variety of pigging launch and receiving systems, including:

• Pneumatic Launchers and Receivers: These systems use compressed air to launch and receive pigs. They are relatively simple and cost-effective but may not be suitable for all pipeline conditions or pig types. I’ve worked with various pneumatic systems, from smaller portable units to larger, more complex systems used on major pipelines.

• Hydraulic Launchers and Receivers: These use hydraulic pressure to launch and receive pigs, offering greater control and precision compared to pneumatic systems. They are often used in applications requiring higher pressure or more complex pigging operations. My experience includes working with both systems in various applications, noting the challenges of precise pressure control and potential issues with hydraulic leaks.

• Combination Systems: Some systems utilize a combination of pneumatic and hydraulic components. These offer the benefits of both technologies. I’ve found these most adaptable to varied pigging scenarios.

My experience also extends to different types of launchers and receivers designed for specific pipeline configurations, including those suitable for vertical or inclined pipelines. Each system has its own advantages and disadvantages, and the selection depends on the specific application and pipeline characteristics. Proper maintenance and regular inspection are critical for the reliable performance of any of these systems.

Unexpected events during pigging operations require a calm, methodical response. Our pre-planned emergency procedures are crucial. These procedures detail actions for various scenarios, such as pig sticking (pig becoming lodged), pipeline leaks, or equipment malfunctions. For instance, if a pig sticks, we first attempt to free it using a variety of methods, including increased pressure, changing pigging fluid, or deploying a follow-up pig to push it through. If these initial steps fail, we’ll initiate a pipeline isolation protocol to prevent further issues. This involves closing valves strategically to isolate the affected section. We then use specialized tools, like fishing tools or pig retrievers, to remove the stuck pig. Communication is critical. The entire team, from the control room to the field personnel, is kept informed throughout the incident. A post-incident review is always conducted to analyze what happened, identify contributing factors, and implement improvements to prevent recurrence. We might even adjust our pigging fluid or pig design for that particular pipeline section based on our learnings.

Pig tracking and monitoring are essential for efficient and safe pigging operations. Think of it like tracking a package – you need to know its location and status to ensure timely delivery. In pigging, we use various methods to track the pig’s progress. This could involve pressure sensors along the pipeline that detect the pig’s passage, sophisticated telemetry systems built into the pig itself sending real-time data (speed, location, internal pressure), or even simple timing observations at access points. Real-time monitoring enables us to identify potential problems early on, such as a slow-moving pig (possibly indicating a blockage) or an unexpected pressure drop (possible leak). Early detection drastically reduces the risk of costly repairs, production downtime, and even environmental damage. Data collected during pig tracking allows for optimization of future pigging runs and provides valuable data for pipeline integrity assessments.

Ensuring pipeline integrity after pigging involves a multi-step approach. Immediately following the operation, we carefully inspect the pipeline for any signs of damage, such as dents, scratches, or leaks, particularly near access points. We perform a thorough pressure test to ensure the pipeline can withstand operating pressures. Visual inspection using cameras inserted into the pipeline, especially in difficult-to-access sections, is common. Specialized tools can also help assess the inner wall for any signs of corrosion or erosion. Pigging itself can sometimes reveal pre-existing problems; a pig might encounter unexpected resistance or even be damaged by an existing pipeline defect. We document all findings, including any repairs made and the results of all inspections. This comprehensive approach minimizes the risk of future pipeline failures and ensures the safe and reliable operation of the system. Regular internal inspections are scheduled even beyond the immediate post-pigging assessment.

Environmental considerations in pigging are paramount. We carefully manage pigging fluids to minimize environmental impact. This includes choosing environmentally friendly fluids and implementing robust spill prevention and containment plans. Proper disposal of spent fluids is crucial, following all applicable regulations and minimizing the volume of waste produced. Potential leaks during the operation are considered a significant risk, and we have emergency response plans ready to address any spills. The selection of pigging fluids itself considers the potential environmental impact. Water-based or biodegradable fluids are often preferred over harsh chemicals, reducing the risk of soil or water contamination. Regular audits and training on environmental best practices are conducted to ensure we uphold the highest environmental standards.

My experience encompasses a wide range of pigging fluids, each with its unique properties and applications. I’ve worked extensively with water-based fluids, which are cost-effective and generally safe for the environment. These are ideal for pipelines carrying non-corrosive materials. I’ve also used glycol-based fluids in applications requiring enhanced lubricity or freeze protection in colder climates. For highly viscous products, we often utilize specialized fluids to ensure efficient pig movement. In cases where product residue is a concern, we select cleaning fluids specifically designed to remove buildup. The choice of fluid is always tailored to the specific product being pigged, the pipeline material, and environmental regulations. I’ve even been involved in projects using foam pigs for specific cleaning tasks, optimizing the process for both effectiveness and minimal environmental impact.

Selecting the appropriate pigging fluid depends on several factors. First, we consider the pipeline’s material (steel, plastic, etc.) and diameter to avoid any incompatibility. The fluid’s viscosity is critical, needing to be balanced for efficient pig movement without excessive pressure. We must also account for the product being pigged – its viscosity, corrosiveness, and temperature. The fluid needs to effectively clean the pipeline without harming the product or the pipeline itself. Environmental regulations are a major factor, favoring biodegradable fluids. Cost is also a consideration, balancing performance against budget. In some cases, we may test different fluids to determine which performs best in a specific pipeline system, ensuring efficiency and minimal environmental impact. For example, a pipeline transporting a highly viscous crude oil would require a different fluid than one carrying a thinner liquid product.

Maintaining and calibrating pigging equipment is crucial for safe and effective operations. This involves regular inspections of all components, checking for wear and tear, corrosion, or damage. Pig launchers and receivers are inspected for leaks or mechanical defects. Pigs themselves are meticulously examined for any damage or deformation that might hinder their movement or performance. Pressure gauges and other instrumentation are calibrated against traceable standards to ensure accuracy. We maintain detailed records of all maintenance activities and calibrations, following a strict preventative maintenance schedule. This proactive approach helps to prevent costly downtime and ensures the continued safe and efficient operation of the pigging equipment. It is vital that all personnel involved in maintenance are properly trained and certified to work on high-pressure systems.

Pigging technologies, while highly efficient, have limitations depending on the type of pig and pipeline conditions. For example, cup pigs, ideal for cleaning relatively large debris, may struggle with fine particulate matter. Scraper pigs, excellent at removing deposits, can be damaged by sharp protrusions within the pipeline. Foam pigs, used for cleaning and drying, are less effective in pipelines with significant bends or changes in diameter. Magnetic pigs, used for inspection and intelligent pigging, require specific pipeline materials to function correctly and are susceptible to interference. Furthermore, all pigging technologies are affected by pipeline geometry; extreme bends, sudden changes in diameter, and the presence of obstacles can hinder or damage the pig. The viscosity of the product being transported also influences pigging efficiency, with highly viscous fluids presenting greater challenges. The pipeline’s internal condition also plays a crucial role. Significant corrosion or damage can render pigging operations unsafe or ineffective.

Pipeline cleaning using pigs involves several key steps. First, a thorough pipeline inspection is conducted to identify potential issues and hazards. Next, the pig is launched into the pipeline using a specially designed launcher. A liquid such as water or a cleaning fluid is often used to propel the pig. The pig then travels through the pipeline, scraping, pushing, or cleaning the material being removed. The choice of cleaning fluid depends on the type of deposit to be removed. After the pig has traversed the pipeline, it’s retrieved at a receiving facility using a pig receiver. This process ensures safety and prevents potential damage to the pig or the pipeline. Post-pigging, the pipeline is inspected again to ensure complete cleaning and identify any potential damages to the pipeline that may have been exacerbated by the process. Finally, the pipeline is prepared for its intended purpose, whether for transporting the product or for further maintenance activities.

My experience spans a wide range of pipeline diameters, from small-diameter gas lines (2 inches) to large-diameter crude oil pipelines (48 inches). I’ve worked with various pipeline materials including steel, polyethylene, and fiberglass reinforced plastic (FRP). Each material presents unique challenges. Steel pipelines can be prone to corrosion, requiring careful pig selection and operation to avoid damage to the pig. Polyethylene pipelines are flexible, which affects pig speed and potential for pig damage. FRP pipes are stronger and lighter than steel, however, they can require a specialized pig design to avoid damage to their inner lining. In larger diameter pipelines, the logistics of launching and receiving the pigs become more challenging, demanding specialized equipment and procedures. Smaller diameter pipelines present their own difficulties with potential for increased pig friction and pressure requirements.

For instance, during a project involving a 36-inch steel pipeline transporting heavy crude oil, we encountered significant asphaltene deposition. We had to use a specialized scraper pig with enhanced cleaning capabilities to remove the heavy deposits effectively, while carefully monitoring pressure and temperature to prevent the pig from getting stuck or damaging the pipeline.

Safety is paramount during pigging operations. We implement rigorous safety protocols at every stage, starting with a detailed risk assessment before operations. This includes identifying potential hazards, such as high pressure, hazardous materials, and confined space entry. Personnel are required to undergo comprehensive training on safe operating procedures and emergency response plans. Proper personal protective equipment (PPE), such as hard hats, safety glasses, and protective clothing is mandatory. Lockout/Tagout procedures are strictly enforced to prevent accidental release of pressure or energy. Regular inspections of equipment and pipelines are performed to ensure everything is in safe working order. Emergency shutdown systems are readily available and personnel are trained in their operation. Detailed emergency response plans are prepared and communicated to all involved. During the actual pigging operation, strict communication protocols are observed and constant monitoring of pressure, temperature, and pig location is maintained. Post-operation, the equipment is thoroughly inspected, and a post-operational report is generated to document the process and identify any safety concerns or improvements required.

The cost of pigging operations is multifaceted. Initial investment includes the cost of pigs, specialized launching and receiving equipment, and potentially cleaning fluids. Operating costs encompass labor, transportation, pipeline downtime, and maintenance of equipment. The frequency of pigging impacts the total cost; more frequent pigging means higher operating costs, but reduces the risk of more significant problems later. The type of pig used significantly impacts cost, with specialized pigs for specific tasks costing substantially more. The pipeline’s length and diameter, and the nature of the deposit or material being removed also influences the duration and overall cost of pigging operations. Unexpected issues, such as a pig becoming stuck, may lead to substantial additional costs associated with retrieval and pipeline repair. A comprehensive cost analysis, considering all these factors, is crucial for effective project planning and budgeting.

Pigging is crucial for maintaining pipeline integrity by removing deposits, preventing corrosion, and ensuring efficient operation. Accumulated deposits like wax, hydrates, or scale reduce pipeline capacity, increase pressure drop, and can lead to blockages. These deposits can also promote corrosion, weakening the pipeline’s structure. Regular pigging removes these build-ups, maintaining optimal flow capacity and preventing potential failures. Furthermore, some pigs incorporate inspection tools enabling early detection of corrosion, cracks, or other structural defects, preventing catastrophic failures. By removing internal obstructions, pigging minimizes the risk of pressure surges and potentially dangerous situations. In essence, pigging is a preventative maintenance strategy, protecting the pipeline’s longevity and safety.

Optimizing pigging procedures for efficiency and cost-effectiveness requires a strategic approach. This begins with accurate pipeline modelling and simulation to predict pig behavior and optimize launch and receiving strategies. Selecting the right type of pig for the specific application is essential. Using data analysis on past pigging operations helps to determine optimal pigging frequency based on deposit accumulation rates and pipeline characteristics. Efficient planning and scheduling of pigging operations minimizes downtime and reduces associated costs. Regular maintenance and inspection of pigging equipment prevent breakdowns and unexpected delays. Implementing advanced technologies, such as intelligent pigs with integrated sensors that provide real-time data on pipeline conditions, helps in optimizing the process and reduces the need for frequent pig runs. Continuous improvement through data analysis and feedback from past operations allows for refinement of procedures and selection of optimal parameters, reducing costs and improving efficiency over time.