Interview Questions for Plant Modifications and Upgrades

HAZOP (Hazard and Operability) studies are crucial for identifying potential hazards and operability problems in plant modifications. They involve a systematic examination of the plant’s processes and equipment, considering deviations from normal operating conditions. My experience encompasses leading and participating in numerous HAZOP studies, from small modifications to major plant overhauls. I’m proficient in facilitating HAZOP sessions, guiding the team through a structured approach using predefined guide words (e.g., ‘more,’ ‘less,’ ‘no,’ ‘part of’) to explore potential deviations. We meticulously document all identified hazards, assess their risks, and develop appropriate mitigation strategies. For instance, during a recent upgrade involving a new reactor, the HAZOP study revealed a potential for overpressure due to a malfunctioning relief valve. This led to the implementation of additional safety interlocks and improved alarm systems.

A key element of my HAZOP approach is ensuring the involvement of diverse team members with relevant expertise, including engineers, operators, and safety specialists. This interdisciplinary perspective allows for a comprehensive evaluation of potential hazards and the development of robust mitigation measures.

Managing change orders during plant upgrades is a delicate balancing act between project scope, budget, and schedule. My approach involves a structured process beginning with a clear change order request form that includes detailed descriptions, justification, and impact assessments. Each change request is reviewed by a cross-functional team to assess its feasibility, cost implications, and schedule impact. This team typically includes engineering, procurement, construction, and project management representatives. We then utilize a formal change control process to track the status of each request. This process includes authorization levels based on the impact and cost of each change. Critical changes might require higher-level approvals before implementation. For example, if a critical component requires a substitution, we follow a strict process involving technical evaluation, vendor qualification, and rigorous documentation.

Transparency is paramount. All stakeholders are kept informed of the status of change orders, and any potential impacts on the project timeline or budget are proactively communicated. We utilize project management software to track all changes and their impact on project deliverables.

Ensuring compliance with safety regulations during plant modifications is a top priority. This involves meticulous adherence to all relevant codes, standards, and permits. Before any modification work begins, we conduct thorough risk assessments to identify potential hazards and develop control measures. We ensure that all contractors and personnel involved receive adequate safety training and work permits before they commence work. Regular safety inspections are conducted throughout the modification process to identify and rectify any unsafe conditions. We meticulously document all safety procedures, inspections, and findings.

For example, during a recent modification to a high-pressure pipeline system, we strictly adhered to the relevant ASME codes and conducted pressure testing and non-destructive examination (NDE) of the welds to ensure integrity. Our process also includes maintaining detailed records of all safety training provided and ensuring compliance with lockout/tagout procedures. This rigorous approach to safety not only ensures compliance but also helps minimize the risk of accidents.

Optimizing plant processes after upgrades requires a multifaceted approach. It starts with establishing clear Key Performance Indicators (KPIs) that align with the goals of the upgrade. These might include improved throughput, reduced energy consumption, or enhanced product quality. We then utilize data analytics to analyze plant performance before and after the modifications. This data-driven approach helps identify areas for improvement and provides insights into the effectiveness of the implemented changes.

Techniques like process simulation and modeling can also help optimize operating parameters and identify potential bottlenecks. For instance, after a recent upgrade to a distillation column, we used process simulation to optimize reflux ratios and achieve significant improvements in separation efficiency and energy savings. Continuous monitoring and feedback loops are also crucial for maintaining optimal performance and identifying any issues that may arise after the upgrade.

During a plant modification involving the integration of a new control system, we encountered a malfunctioning communication interface between the new system and an existing piece of equipment. The initial diagnosis pointed to a hardware fault, but after a thorough investigation, including reviewing the communication protocols and conducting signal tracing, we discovered a software configuration error in the new control system.

Our troubleshooting approach involved a systematic process of elimination: we checked hardware connections, tested the communication links using diagnostic tools, and systematically reviewed the software configuration parameters. We used loop diagrams and process and instrumentation diagrams (P&IDs) to isolate the problem to a specific component. Once the software error was identified and corrected, the system functioned correctly. This incident highlighted the importance of detailed documentation, thorough testing, and a systematic troubleshooting approach during plant modifications.

Managing project timelines and budgets for plant upgrades necessitates a robust project management plan. This begins with a detailed scope definition, a work breakdown structure (WBS), and a realistic project schedule. We utilize critical path method (CPM) analysis to identify critical activities and manage dependencies. Regular progress monitoring, including weekly status meetings and performance reporting, is integral to early detection of deviations and timely corrective actions. Budget tracking involves meticulous cost accounting, variance analysis, and proactive management of potential cost overruns. We employ earned value management (EVM) techniques to monitor project performance and make necessary adjustments to the schedule and budget as needed.

For example, we might use Gantt charts to visualize the project schedule and identify potential conflicts. Any change requests are carefully assessed for their cost and schedule implications before approval. This proactive approach minimizes risks and enhances the likelihood of delivering the project on time and within budget.

My experience encompasses a wide range of plant equipment, including reactors, distillation columns, heat exchangers, pumps, compressors, and control systems. I’ve worked with various types of process control systems, including programmable logic controllers (PLCs) and distributed control systems (DCS). My expertise extends to different materials of construction, from stainless steel to exotic alloys, depending on the process conditions. I’m familiar with the operational characteristics and maintenance requirements of diverse equipment and understand the impact of different process parameters on equipment performance.

For example, I’ve been involved in projects involving the upgrading of centrifugal pumps in a chemical plant, the replacement of heat exchangers in a refinery, and the installation of a new DCS in a pharmaceutical manufacturing facility. This broad experience allows me to effectively assess the technical feasibility of plant modifications and to recommend cost-effective solutions that meet the project’s goals.

Plant modifications encompass a wide range of techniques, broadly categorized into retrofits and expansions. Retrofits involve upgrading existing equipment or systems to improve efficiency, safety, or compliance. This could be as simple as replacing outdated valves with more energy-efficient ones or as complex as integrating a new control system. Expansions, on the other hand, increase the plant’s capacity by adding new units or modifying existing ones to handle larger volumes. Think adding a new production line to increase output or expanding storage tanks to accommodate increased production.

• Retrofits: I’ve worked on numerous retrofits, including replacing aging PLC controllers in a chemical plant with a modern SCADA system, resulting in improved data acquisition and process control. Another example involved retrofitting a power plant with flue gas desulfurization equipment to meet stricter environmental regulations.
• Expansions: I participated in the expansion of a food processing plant by adding a new packaging line. This involved detailed planning for integration with existing infrastructure, including utilities, logistics, and safety systems.

My experience spans various industries, including chemical processing, power generation, and food manufacturing, giving me a broad understanding of the unique challenges and considerations in each.

Risk assessment in plant modifications is paramount. It’s a systematic process of identifying, analyzing, and evaluating potential hazards associated with the modification. This isn’t just about safety; it also considers potential impacts on production, environmental compliance, and budget. We use a combination of qualitative and quantitative methods.

• Hazard Identification: We use techniques like HAZOP (Hazard and Operability Study) and What-If analysis to systematically identify potential hazards. For example, during a piping modification, we’d consider potential leaks, fires, or equipment damage.
• Risk Analysis: We assess the likelihood and severity of each identified hazard. A risk matrix helps visualize this, prioritizing risks based on their potential impact.
• Risk Mitigation: Once risks are identified and assessed, we develop mitigation strategies. These might include engineering controls (e.g., installing safety valves), administrative controls (e.g., improved training), or personal protective equipment (PPE).

A well-executed risk assessment minimizes the probability of incidents and ensures a smooth and safe modification process. I’ve personally led numerous risk assessments, ensuring that our team is fully aware of potential hazards and has plans in place to address them.

Unexpected issues are inevitable in plant upgrades. My approach involves a structured problem-solving methodology focusing on swift response and effective communication.

1. Immediate Response: First, we secure the area, ensuring the safety of personnel and equipment. This might involve shutting down affected parts of the plant.
2. Problem Diagnosis: We conduct a thorough investigation to determine the root cause of the problem. This often requires collaboration with engineers, technicians, and operations personnel.
3. Solution Development: We brainstorm potential solutions, evaluating their feasibility and impact. This might involve temporary workarounds or more permanent fixes.
4. Implementation and Verification: We implement the chosen solution, carefully testing and verifying its effectiveness before resuming normal operations.
5. Lessons Learned: Finally, we conduct a post-incident review to document the problem, the solution, and lessons learned to prevent similar issues in the future.

For example, during a recent upgrade, we encountered an unexpected compatibility issue between the new control system and an existing piece of equipment. By following this methodology, we quickly identified the problem, implemented a temporary workaround, and developed a permanent solution while minimizing downtime.

My experience encompasses various process control systems, from traditional pneumatic and hydraulic systems to modern distributed control systems (DCS) and programmable logic controllers (PLCs). I am also familiar with advanced process control (APC) strategies.

• Pneumatic and Hydraulic Systems: While less common now, understanding these older systems is crucial for working with legacy equipment. I’ve worked on projects that involved integrating these older systems with modern control systems.
• PLCs (Programmable Logic Controllers): I’m proficient in programming and troubleshooting various PLC platforms, such as Allen-Bradley and Siemens. I’ve developed numerous PLC programs for controlling various processes, from conveyor systems to automated packaging lines.
• DCS (Distributed Control Systems): I have extensive experience with DCS platforms like Emerson DeltaV and Honeywell Experion. I’ve worked on projects involving DCS upgrades, modifications, and integration with other systems.
• SCADA (Supervisory Control and Data Acquisition): I’m experienced in configuring and maintaining SCADA systems, allowing for real-time monitoring and control of plant processes.

My experience spans different system architectures and communication protocols, enabling me to effectively design, implement, and maintain control systems in various plant environments.

Ensuring quality is paramount. We implement a multi-layered approach combining rigorous planning, strict adherence to procedures, and meticulous quality control checks.

• Detailed Engineering Design: The foundation of quality is a thorough and accurate engineering design. This includes detailed specifications, drawings, and simulations.
• Material Selection and Procurement: We use only high-quality materials from reputable suppliers, ensuring compliance with industry standards and specifications.
• Workmanship Standards: Our technicians are highly skilled and adhere to strict workmanship standards. Regular training and supervision ensure consistent quality.
• Quality Control Inspections: We conduct regular inspections at various stages of the project, from material inspection to final commissioning. This ensures that all work meets the required standards.
• Documentation: Comprehensive documentation is maintained throughout the project, including design documents, inspection reports, and as-built drawings.

For instance, in a recent project, we implemented a rigorous inspection program that identified a minor welding defect before it could affect the overall system’s integrity. This proactive approach prevented potential issues down the line.

Minimizing downtime during plant upgrades is critical for maintaining production and profitability. Our strategies include meticulous planning, phased implementation, and parallel work execution.

• Detailed Planning and Scheduling: We develop a detailed project schedule that identifies critical path activities and potential delays. This involves close coordination with operations and maintenance teams.
• Phased Implementation: Where possible, we break down the upgrade into smaller phases, allowing for incremental implementation and minimizing the overall impact on production.
• Parallel Work Execution: We optimize the project timeline by executing tasks in parallel whenever possible, without compromising safety or quality.
• Pre-Commissioning and Testing: Thorough pre-commissioning and testing are conducted off-line whenever possible to identify and address issues before they impact production.
• Optimized Shutdown Procedures: We work closely with operations to develop optimized shutdown and startup procedures to minimize downtime.

In one project, we successfully reduced downtime by 30% by implementing a phased approach and using parallel work streams, ultimately saving the client significant revenue losses.

Knowledge of industry standards and codes is fundamental. We rigorously adhere to relevant standards, such as those published by ASME (American Society of Mechanical Engineers) and API (American Petroleum Institute), as well as other relevant national and international codes.

• ASME Codes: These are essential for pressure vessel design, fabrication, and inspection. We ensure that all pressure vessels and related equipment meet the appropriate ASME codes (e.g., ASME Section VIII).
• API Standards: In the oil and gas industry, API standards guide many aspects of plant design, construction, and operation. We follow relevant API standards for piping, storage tanks, and other equipment.
• Other Relevant Codes: Depending on the project and industry, other relevant codes and standards are applied, including those related to electrical safety, fire protection, and environmental regulations.

Compliance with these standards is not just about meeting legal requirements; it’s about ensuring plant safety, reliability, and longevity. Our team includes engineers certified in relevant standards, guaranteeing compliance and minimizing risks.

Collaboration is the cornerstone of successful plant modification projects. I approach this by fostering open communication and proactive engagement with various teams, including engineering, procurement, construction, safety, and operations.

• Early Involvement: I ensure all relevant teams are involved from the initial planning stages, contributing their expertise to identify potential challenges and streamline the process. This prevents costly rework later.
• Regular Meetings: We hold regular meetings, often using a collaborative project management tool, to discuss progress, address challenges, and make informed decisions collectively. This maintains transparency and ensures everyone is aligned.
• Defined Roles and Responsibilities: Clear roles and responsibilities are established upfront to avoid duplication of effort and ensure accountability. A robust communication plan outlines how information will be shared and who is responsible for what.
• Conflict Resolution: I actively participate in resolving conflicts that may arise between teams, often by facilitating discussions and finding mutually agreeable solutions. The goal is always to prioritize the project’s overall success.

For example, during a recent upgrade of a process control system, I worked closely with the IT team to ensure seamless integration with existing network infrastructure. This collaborative approach avoided potential downtime and system conflicts.

I possess extensive experience using various plant design software packages. My expertise includes AutoCAD for 2D drafting and detailed design, and PDMS (Plant Design Management System) for 3D modeling and data management of complex plant layouts.

• AutoCAD: I’m proficient in creating detailed drawings, including P&IDs (Piping and Instrumentation Diagrams), layouts, and isometrics. I leverage AutoCAD’s tools for efficient design and documentation, ensuring accuracy and consistency.
• PDMS: I’m skilled in developing 3D models, clash detection, and managing the entire plant’s data within the PDMS environment. This allows for the identification of potential interference issues before construction begins, saving time and resources.
• Other Software: I also have experience with other relevant software like Navisworks for model review and collaboration, and various simulation tools for process optimization.

For instance, on a recent refinery upgrade, I utilized PDMS to create a comprehensive 3D model of the modifications, allowing for a thorough clash detection analysis that prevented construction delays and rework. This ensured a smoother and more efficient project execution.

Validating the effectiveness of plant modifications is crucial to ensure they meet the intended objectives and performance targets. This involves a combination of pre- and post-modification assessments.

• Pre-Modification Analysis: This involves thorough simulation and modeling to predict the impact of the modifications on the plant’s performance. We use tools to evaluate changes to process parameters, energy efficiency, and safety.
• Testing and Commissioning: After the modifications are implemented, a rigorous testing and commissioning phase ensures all equipment and systems function as designed. This includes individual component testing and integrated system tests.
• Performance Monitoring: Post-modification, continuous performance monitoring is crucial. Key parameters are tracked to validate improvements and identify any unexpected issues. This data provides valuable insights for future upgrades.
• Data Analysis: Statistical analysis of the collected data compares pre- and post-modification performance, allowing for a quantitative assessment of the effectiveness of the changes.

For example, during a boiler efficiency upgrade, we used performance monitoring data to verify the predicted fuel savings and validate the design’s effectiveness. The data conclusively showed a significant improvement, justifying the investment.

Commissioning and start-up procedures are critical phases in plant modification projects. My experience covers all aspects, from planning and preparation to final handover.

• Pre-Commissioning: This involves inspecting all equipment and systems to ensure they are installed correctly and meet specifications. This often includes pressure testing of piping systems and electrical checks.
• Commissioning: This is a systematic process of testing and verifying each system individually and as part of the integrated plant. This involves detailed checklists, procedures, and documentation.
• Start-Up: I participate in the controlled and gradual start-up of the modified systems, ensuring safe and efficient operation. This involves monitoring critical parameters and adjusting settings as needed.
• Handover: Finally, I work with the operations team to ensure a smooth transition and provide training on the new or modified systems.

In a recent project involving the installation of a new process control system, I played a key role in developing the commissioning plan, overseeing the testing phase, and leading the start-up process, ensuring a successful and safe transition to the upgraded system.

Meticulous documentation and record-keeping are essential for plant modifications, ensuring compliance, traceability, and efficient future maintenance. I use a structured approach to manage this crucial aspect.

• Document Control System: I implement a robust document control system to manage all drawings, specifications, procedures, and test results. This often involves using a dedicated software system.
• Version Control: We strictly adhere to version control protocols to prevent confusion and ensure everyone is working with the latest revised documents. This avoids potential errors and ensures consistency.
• As-Built Drawings: Maintaining accurate as-built drawings is critical for future modifications or maintenance. Any deviations from the original design are recorded and updated in the as-built documents.
• Electronic Data Management: I prioritize the use of electronic document management systems for easy access, sharing, and archiving. This improves efficiency and reduces reliance on paper-based documentation.

For example, in a large-scale plant upgrade project, our electronic document management system was instrumental in providing seamless access to all project-related documents for all involved teams. This drastically reduced confusion and improved the overall project efficiency.

My experience encompasses a wide range of piping systems, from standard carbon steel to specialized materials for demanding applications. I understand the design, material selection, and installation requirements for each type.

• Carbon Steel Piping: This is the most common type and requires knowledge of appropriate welding techniques, corrosion protection, and pressure testing procedures.
• Stainless Steel Piping: Often used in applications requiring high corrosion resistance, this requires specialized welding and fabrication techniques to ensure integrity.
• High-Pressure Piping: These systems necessitate rigorous design calculations, material selection, and stringent quality control measures.
• Instrumentation Piping: This includes small-bore piping for instrument air, sample lines, and other instrumentation, requiring precise installation and leak testing.

For instance, in a recent project involving the upgrade of a chemical processing plant, I oversaw the selection and installation of stainless steel piping for corrosive process streams. My expertise in selecting appropriate materials and ensuring proper welding techniques helped prevent potential corrosion and process upsets.

Ensuring the integrity of plant equipment after modifications is paramount for safe and reliable operation. This requires a multi-faceted approach.

• Non-Destructive Testing (NDT): Techniques like radiography, ultrasonic testing, and visual inspections are used to verify the integrity of welds and detect any flaws in materials after modifications.
• Pressure Testing: This is conducted to verify the strength and leak tightness of piping and pressure vessels after modifications.
• Equipment Alignment and Vibration Analysis: Precise equipment alignment is crucial to prevent vibration and premature wear. Vibration analysis is used to identify potential issues after modifications.
• Post-Modification Inspections: Thorough inspections are conducted to ensure that all modifications have been completed according to specifications and that no damage occurred during the installation process.

For example, during the installation of a new pump, we conducted rigorous pressure testing and vibration analysis to ensure its proper function and to prevent potential issues like bearing failure or pipe leaks. This proactive approach ensured the long-term integrity of the equipment and the overall system.

Preventative maintenance programs are crucial for extending the lifespan of plant equipment and preventing costly breakdowns. My experience encompasses developing and implementing comprehensive programs that focus on proactive inspections, lubrication schedules, and predictive analytics. This involves:

• Risk Assessment: Identifying critical equipment and potential failure points through Failure Modes and Effects Analysis (FMEA).
• Scheduled Maintenance: Creating detailed schedules for routine tasks like cleaning, lubrication, and inspections, using CMMS (Computerized Maintenance Management System) software for tracking and scheduling.
• Predictive Maintenance: Utilizing sensors and data analytics to monitor equipment performance in real-time, predicting potential failures before they occur. For instance, we might use vibration analysis on pumps to detect impending bearing failures.
• Spare Parts Management: Maintaining optimal inventory levels of critical spare parts to minimize downtime during repairs. This often involves implementing Just-In-Time (JIT) inventory strategies.
• Documentation and Reporting: Meticulous record-keeping of all maintenance activities, allowing for continuous improvement of the program and identification of recurring issues. This includes generating reports on maintenance costs, downtime, and equipment performance.

For example, in a previous role, I implemented a predictive maintenance program for a bottling plant that reduced unplanned downtime by 40% within a year by using vibration sensors on conveyor belts to predict failures and schedule preventative maintenance before they occurred.

Identifying and prioritizing plant upgrade needs is a systematic process. I typically start with a thorough assessment of the current plant’s performance, considering factors like:

• Production Capacity: Is the current plant meeting production targets? Are there bottlenecks limiting output?
• Equipment Reliability: What is the frequency of equipment failures? What is the associated downtime cost? A high failure rate points to a need for upgrade or replacement.
• Energy Efficiency: Are there opportunities to reduce energy consumption through upgrades to motors, pumps, or control systems? This often offers a strong return on investment.
• Safety and Compliance: Does the plant comply with all relevant safety regulations? Are there any safety hazards that need addressing through equipment upgrades?
• Technological Advancements: Are there newer technologies that could significantly improve efficiency, productivity, or product quality?

Prioritization often involves a cost-benefit analysis and return on investment (ROI) calculation for each potential upgrade. Upgrades with the highest ROI and lowest risk are typically prioritized. A simple scoring system can also be used, assigning weights to factors like production improvement, cost savings, and safety implications.

Lifecycle cost analysis (LCCA) is crucial for making informed decisions about plant upgrades. It’s a method of evaluating the total cost of ownership of an asset over its entire lifespan, from initial investment to eventual disposal. This includes:

• Initial Investment Costs: Purchase price of equipment, installation costs, and any necessary modifications.
• Operating and Maintenance Costs: Energy consumption, labor costs for operation and maintenance, spare parts, and regular servicing.
• Repair and Replacement Costs: Expected costs of repairs and replacements during the asset’s lifespan.
• Disposal Costs: Costs associated with removing and disposing of the equipment at the end of its life.

By considering all these factors, LCCA helps to identify the most cost-effective upgrade option over the long term. For instance, an initial investment in a more energy-efficient piece of equipment might have a higher upfront cost, but the reduced operating costs over time could result in a lower overall lifecycle cost compared to a cheaper, less efficient alternative.

Data analytics plays a vital role in improving plant efficiency post-modifications. By collecting and analyzing data from various sources—sensors on equipment, production records, energy meters—we can gain valuable insights into the impact of modifications and identify areas for further improvement. This often involves:

• Performance Monitoring: Tracking key performance indicators (KPIs) like Overall Equipment Effectiveness (OEE), production output, energy consumption, and waste generation before and after the modifications to assess the impact.
• Predictive Modeling: Using machine learning algorithms to predict equipment failures, optimize production schedules, and anticipate potential bottlenecks.
• Root Cause Analysis: Identifying the root causes of any remaining inefficiencies or unexpected issues after the modifications, often using statistical process control (SPC) charts.
• Process Optimization: Using data-driven insights to fine-tune processes, improve resource allocation, and reduce waste.

For example, after implementing a new control system, we might use data analytics to identify optimal control parameters that maximize production while minimizing energy consumption. We might also use machine learning to predict equipment maintenance needs and optimize scheduling to minimize downtime.

Training personnel on new equipment or processes is critical for successful implementation and safe operation. My strategies involve a multi-faceted approach:

• Needs Assessment: Identifying the specific training needs of the personnel based on the complexity of the new equipment or processes.
• Modular Training: Breaking down the training into smaller, manageable modules, allowing for a more effective learning process.
• Hands-on Training: Providing ample opportunities for hands-on practice with the new equipment or processes in a controlled environment.
• Simulations and Virtual Reality: Utilizing simulations and VR technology to replicate real-world scenarios and allow personnel to practice in a safe and controlled environment.
• On-the-Job Training (OJT): Providing supervised training on the actual equipment or processes within the plant.
• Continuous Evaluation and Feedback: Regularly evaluating the effectiveness of the training and providing feedback to trainees.
• Documentation and Reference Materials: Providing comprehensive documentation and reference materials for future use.

For example, when implementing a new robotic welding system, we might start with classroom training covering the basics of robot operation and safety procedures. This would be followed by hands-on training using a simulator, and finally, on-the-job training under the supervision of experienced technicians.

One challenging project involved upgrading the control system of a large chemical plant. The challenge was to complete the upgrade without interrupting production, which was crucial for maintaining the plant’s output and revenue stream. This involved:

• Phased Implementation: We divided the upgrade into phases, upgrading different sections of the plant sequentially to minimize disruption. This required careful planning and coordination to ensure seamless transitions between phases.
• Redundancy and Backup Systems: We implemented redundant systems and backups to mitigate the risk of failures during the transition. This meant that if one system failed, the backup system could immediately take over, ensuring uninterrupted operation.
• Detailed Planning and Simulation: We used detailed simulations to test the new control system and identify any potential problems before implementation. This significantly reduced the risk of errors and delays.
• Extensive Training: We provided extensive training to the plant operators on the new system, ensuring a smooth transition and minimizing the learning curve.
• Close Collaboration: Close collaboration with the plant operators and maintenance personnel was crucial to ensure the success of the project. This involved regular meetings and open communication to address any issues or concerns.

Despite the complexities, the project was completed on time and within budget, without any significant disruption to production. The upgraded control system significantly improved efficiency, reduced energy consumption, and enhanced the overall safety of the plant.