When conducting time-based leak/closure tests, two types of valves are typically considered. The first type involves fully closing wellhead valves every 3 months to prevent internal passing. The second type requires partially closing control valves every few months to ensure they will fully close during safety-critical situations, such as plant trips. Have you ever wondered about the reasoning behind the frequency of these preventative maintenance checks?
A useful guideline to follow is to consider conducting a test for hidden failures. If the majority of valves fail the test, it may indicate that your maintenance interval is too long. Additionally, if the failures can be categorized by area, model, type, or application, it is recommended to further investigate and identify any potential issues.
Thank you for your feedback. I am interested in understanding the rationale behind starting at 3 months, such as the optimal frequency determined by studies, especially in the context of control valves in a refinery. I am aware of a study on optimizing PSV prepop testing and overhaul, showing that PSVs in corrosive environments like water service are more prone to failure compared to those in clean/dry steam or gas service. Therefore, it is important to prioritize maintenance in the former.
Is there a specific rationale behind initiating a 3-month duration? Planning for a 3-month timeframe is straightforward, but it is crucial to also factor in potential repercussions of failure, environmental impacts, and compliance with regulations. For instance, when looking at steam boilers, regular testing and documentation of the Pressure Safety Valve (PSV) is required at least once a month. The consequences of a PSV that fails to lift are widely recognized within the power generation sector.
When it comes to hidden functions, the relationship between required availability, failure rate (MTBF), and test frequency is crucial. The availability on demand is determined by the level of risk we are willing to accept, which is influenced by various factors outlined in a Quantified Risk Analysis. Understanding qualitative risks is also essential in this process. Chapter 7 of my book delves into these risk aspects. Testing for hidden functions is detailed on pages 32-39, with a specific focus on equation 3.13. If you will be attending RCM-2006, I will be presenting a paper on Detective Maintenance that addresses these topics. You can also find a paper on this subject on the Reliabilityweb.com website. V.Narayan.
Hello Josh, I hope everything is going well for you and that your company is off to a successful start in the New Year. I have a question regarding the optimal frequency for starting at 3 months. Is there any research or study available on this topic, specifically in the context of control valves in a refinery? Building on Vee's response regarding testing for hidden failures, it is crucial to consider the relationship between the desired availability, failure rate, and inspection frequency. In SAE JA1012, a formula is used to determine the frequency of inspection based on the failure rates of the protective device and the protected function. This calculation is specific to each plant's operating context and management requirements. It is important to note that the formula is designed for situations with one device and random failure mode. Factors such as multiple devices in series, parallel configurations, and voting systems need to be taken into account when determining the failure finding frequency. Ultimately, the formula aims to manage the level of unavailability within a tolerable risk level for the company. However, when considering economic consequences, the calculation may need to be adjusted to assess the likelihood of monetary impacts rather than tolerable risk levels. I believe Vee will elaborate on this further during his upcoming seminar. Thank you for your attention to this matter.
Great point of discussion! The frequency of these checks seems mainly to trade off between safety and maintenance costs. The goal here is to catch any leaks or faults before they cause serious operational problems or safety hazards. However, more frequent checks imply higher operational downtime and maintenance costs. So, it's all about finding that sweet spot where the cost & inconvenience of the checks are outweighed by the benefits of catching potential issues early. It's also worth noting that regulatory guidelines play a significant role in determining these frequencies, ensuring these critical safety measures meet industry standards.
The frequency of these checks is indeed quite fascinating. When it comes to safety in plants, regularity is crucial. By conducting tests every 3 months, operators are able to identify and manage potential risks proactively. These tests are performed frequently enough to prevent major leaks or failures, but not so often as to cause unnecessary shutdowns. Remember, each shutdown period means time and monetary loss, and a multitude of routine checks could result in unnecessary wear. So, it's about striking the right balance — ensuring safety while optimizing operational efficiency.
Absolutely, the frequency of these checks often stems from a blend of regulatory compliance and risk management strategies. By fully closing wellhead valves every three months, it helps in identifying any potential leaks early on, which is crucial for safety and environmental protection. In contrast, the periodic partial closure of control valves is more about ensuring reliability under pressure during unexpected scenarios. It’s all about striking that balance between proactive maintenance and operational readiness, which can vary significantly across different facilities and their unique risks.
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Answer: 1. Why is it important to conduct regular valve leak and closure tests for preventative maintenance? - Regular valve leak and closure tests are crucial for identifying and preventing internal passing in wellhead valves and ensuring control valves will function properly during safety-critical situations like plant trips.
Answer: - Fully closing wellhead valves every 3 months helps prevent internal passing and ensures the valves are in optimal working condition to maintain operational integrity.
Answer: - Partially closing control valves every few months allows for testing to ensure they will fully close when needed during safety-critical situations, such as plant trips, to maintain operational safety and reliability.
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