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What is a Valve Signature? – Part 2

A valve is a pressure vessel with internal moving parts; and when they move, they encounter resistance from other parts and from the flow. The recording of the pressures and forces associated with overcoming these resistances is sometimes called “valve signature”. When plotted over time, the trends are helpful in identifying degradation and other operational problems.
 
In Part 2 of this article, we will learn more about the compiling of the valve signature, and the benefits derived from it.

By Davi Sampaio Correia – Technical Consultant


Valve Signature and Predictive Maintenance

There are two main usages of valve signatures, depending on how they were acquired. If the signature was collected during design approval, then it can be used for establishing FAT acceptance criteria and also for monitoring wear during the lifecycle of the valve, as seen in the case of the subsea valves. If the signature was collected during the FAT of a valve that had no design approval phase, then the cycling-aging correlation is not possible; but it is still possible to monitor performance if the valve in the field has the adequate instrumentation. Also, it is possible to install the required instrumentation in a valve already operating in a plant. The goal would be to start monitoring wear from the installation moment onward.

Figure 6 has some examples of sensors that can be installed in a valve already operating. A full diagnostic setup for a ball valve generally considers the following:

Figure 6 – Examples of sensors used in the field for valve performance monitoring. Image courtesy of MRC Global.
Figure 6 – Examples of sensors used in the field for valve performance monitoring. Image courtesy of MRC Global.

a) Actuator Pressure Sensor – This sensor is mounted in the pressurized section of either a pneumatic or hydraulic actuator, and it should be compatible with the actuator’s pressure rating. Blocked exhaust, increased friction, and leakage are some of the actuator problems that this sensor allows to uncover.

b) Strain Sensor – This sensor monitors the mechanical performance of the valve and actuator. A strain gauge is mounted directly on the yoke and measures dimensional changes by analyzing the amount of force between the valve and the actuator.(4) Increased friction in the valve can be detected with this sensor.

c) Dynamic Pressure Sensor – These sensors are used to detect leaks in the pipe and the sealed cavity compartment of the valve by using two equal dynamic pressure sensors mounted in the upstream, downstream and cavity positions on the valve. The sensor reports the difference in pressure at both locations. The data they collect is then used to confirm seal integrity.(4)

d) Acoustic Sensor – This non-intrusive sensor is mounted on the valve itself on or on the pipe near the valve. When the valve is in the closed position, this acoustic sensor can detect leaks via monitoring the sound waves generated by the valve. The above sensors allow a company to shift a strategy of corrective maintenance (or preventive maintenance) to predictive maintenance. That is, instead of acting after the failure (corrective) or setting a schedule for intervention that may or may not find the valve in need of repair (preventive), the company can pinpoint with accuracy the better time for replacing or overhauling a valve, before it impacts production. After the valve is serviced, the sensors allow the immediate comparison between baseline data and the valve’s current operating condition. Ball valves used for Emergency Shut Down (ESD) and High-Integrity Pressure Protection System (HIPPS) applications are routinely issued with some variation of the sensors aforementioned. 

Read Part 1 of this article here.


REFERENCES:

1) G. Gokilakrishnan et al, Operating Torque in Ball Valves - A Review, International Journal for Technological Research in Engineering, Volume 2, Issue 4, December-2014 ISSN (Online): 2347 – 4718.
2) Ming-Jyh Chern et al, Performance test and flow visualization of ball valve, Experimental Thermal and Fluid Science 31 (2007) 505–512.
3) Jeeves et al, Predicting Valve Failures in the Digital Age of Valve Management, presented at the Abu Dhabi International Petroleum Exhibition & Conference held in Abu Dhabi, UAE, 11-14 November 2019, SPE-197451-MS.
4) https://www.mrcglobal.com/Global-Region/Products/ValveWatch/Sensors.


ABOUT THE AUTHOR

Davi Correia is a Senior Mechanical Engineer who has worked at a major Brazil-based oil company for the last 15 years. Correia is part of multi-disciplinary team that provides technical support for topside piping and equipment of production platforms. During this period, he began to work with materials and corrosion, and later moved to piping and accessories technology, where he has become one of the lead technical advisors on valve issues. Correia was part of the task force that revised the IOGP S-562 standard, and wrote the S-611 standard. Correia has a master’s and a doctor’s degree in welding by the Universidade Federal de Uberlandia.  

 

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