Valve failure can represent far more than the capital cost of replacing the products. With many operators looking to maximize plant uptime and efficiency, regular monitoring and analysis can help the industry to maintain these essential components proactively and cost effectively.
A refinery that processes 250,000 barrels per day can easily contain thousands of valves. These products span all aspects of a plant’s operations – flow isolation and control, steam management, overpressure protection, recirculation and much more. Given the essential presence and critical functions performed, valves require active maintenance to prevent unnecessary downtime.
Potentially serious consequences
If a valve should fail, there can be a serious risk of environmental impact, production losses, or a threat to the safety of the workforce. According to a study on containing fugitive emissions1, 60 % of such emissions in refineries come from leaking valves, most frequently of which tend to be control valves. As operations become further integrated, one failure can have serious consequences. Add a 24-hour and immediate news cycle, and a single mistake can become a global news story and damage a plant’s reputation beyond repair.
If valves are to be properly maintained to avoid the risk of failure, the question is quite simple, how does a plant operator determine when and how often valves need to be serviced?
Unplanned maintenance increasing
In response to managing the risks associated with valves, operators have increased maintenance spending, averaging $27 billion in 20112. In today’s refineries, this growth is higher than investment is additional plant capacity, demonstrating operators’ need to maximise performance and efficiency from their existing equipment. Even with increased maintenance spending, however, the number of unplanned downtime events continues to increase. 50% of refinery maintenance is now unplanned, double the rate of a decade ago3. In fact, in 2011 alone there were an estimated 2,700 incidents involving product and component issues in refineries.
Plants and refineries are responding to this challenge by increasing valve maintenance planning. This approach helps keep valves serviced and operating properly. Good maintenance planning means doing the right maintenance on the right valve at the right time, with a different approach needed for each valve. Automatically scheduling valve maintenance on a single pre-determined cycle doesn’t take into account the unique operating conditions that an individual valve experiences in service. This results in valves that fail sooner than expected (in between maintenance cycles) or valves that don’t need to be serviced at the maintenance cycle. To optimize maintenance (including reducing the costs of it), a customized and integrated approach to valve maintenance is vital.
Maintenance challenges
An integrated approach to valve maintenance planning requires plants to consider many factors that may contribute to downtime and safety and environmental risks, including:
• Changes to plant process conditions
• Equipment used throughout the plant’s operations and any changes made to it
• Safety records and training of the workforce
• Service records and parts used
• Amount of maintenance needed to avoid failure
• Analysis of repeat breakdowns
• Quantity on hand and availability of spare parts
• Changes in regulations
For many plants, managing records on valve maintenance can be a significant undertaking, particularly if there are no complete or accurate records, or the data is stored in different locations by various personnel. This makes it difficult to optimize maintenance and almost impossible to identify trends. Compounding the issue, operators often choose to schedule regular planned maintenance across the board, hoping that will allow for the repair of any potential problem valves before they fail. This approach can lead to even more issues as it does doesn’t take into account prior performance or repair history.
Moving to a more thorough and regular maintenance schedule to monitor a plant’s valves can be achieved with an asset management solution. Operators work with a service provider to determine a predictive and preventive maintenance schedule customized for the site’s specific valve types, taking into consideration each product’s service and performance history.
Using a predictive maintenance methodology as opposed to an automatic approach, an operator prioritizes maintenance and service based on data that includes experience, observation, historical data, failure modes and testing, coupled with analysis of the probability and impact of a valve failure. This determines when maintenance should be scheduled. A comprehensive asset-management solution includes the following:
• Plant asset data, including testing of all assets as well as an ongoing service schedule for them
• Historical performance of the assets as well as the current condition of the valve and its components
• Inventory management and planning system detailing the location and count of each valve as well as spare parts
• Performance indicator report, with comprehensive metrics and charts showing calibration records and trending information
• Real-time monitoring and diagnostics to track repair cycles and data on assets that will help set maintenance schedules
• Proposed preventive/planned maintenance schedule detailing how often each valve should be scheduled for maintenance based on its performance
Valve asset management techniques
Risk Based Inspection (RBI) is a key analysis technique to achieve the optimum maintenance interval by assessing how likely the valve is to fail and how large the impact of a failure would be.
When assessing the probability of valve failure, inspection detail is carried forward to create an RBI path. Previous inspection history is reviewed and a revised probability score is determined. This score is then mapped to the RBI scheme to get a low, medium or high determination of the probability of failure. When assessing the consequence of valve failure, it is important to involve the process owner as they will have the best viewpoint as to the impact of a failure. They can then discuss and determine what they would consider high, medium and low impact of failure for that valve at that point in the process. Plants can then schedule their maintenance on critical plant areas based on these insights. Considering that 60% of valves are replaced or serviced prematurely5, RBI can offer considerable performance improvement and savings by providing the planning methodology that leads to servicing valves at the right time, not on an averaged schedule.
Another effective technique in an asset management portfolio is Failure Mode & Effects Analysis (FMEA). This type of analysis helps identify potential failures, evaluate the effects of these events, and identify the actions that could eliminate or reduce the chance of the potential failure. By minimizing the risk of valve failure, FMEA helps to maximize valve operational reliability.
Root Cause Failure Analysis (RCFA) is a troubleshooting maintenance method that investigates, analyzes and identifies the root cause of a valve failure. Identifying the root cause of valve failure and utilizing the information to make necessary changes to equipment, processes, or maintenance regimes, can prevent it from happening again. Solutions may involve replacing the valve with a more suitable option or changing a service interval.
Asset management will pay dividends
The benefits of an effective valve asset-management program are improved uptime and reliability, which can in turn optimize maintenance spending. An effective valve asset management system also helps a site avoid duplication of spare parts by improving inventory and availability. The valve population and maintenance schedule are used to optimize spare parts and maintain the right levels without compromising safety and production.
Plant operators must remember that they’re not alone when it comes implementing a valve asset-management program. Close collaboration maximizes the expertise and capability shared between plant operators, valve service providers and valve manufacturers will yield the best results.
The benefits of preventive valve maintenance for a major UK refinery
Scope of work:
• A UK refinery signed a 5-year preventive maintenance contract with Pentair Valves & Controls that was renewable after the period for an additional 5 years. Contract is currently in its 14th year
• An intensive investigation was conducted that was used to feed inputs into the RBI scheme in order to develop the probability and consequence of failure • Service intervals were then analyzed and re-defined based on the inputs
The results:
• Problem valves were identified, analyzed, and issues addressed
• By replacing these problem valves, the safety and performance of the plant was improved
• The average service interval went from 26 to 43 months, saving the refinery $2 million in service costs
• By 2006, 50% of valves required an inspection only every 36 months or less
• By 2011, this was further reduced to 20%
1 Chemical Engineering magazine, June 2010 – www.che.com/ technical_and_practical/5718.html
2 HPI Market Data, 2011
3 IIR, HPI Market Data, BP Statistical Review of World Energy 2011
4 IIR Industrial Info Source, 2012
5 ‘Consider Fieldbus for Retrofit’, Hydrocarbon Processing