Vibrations in hydrocarbon pipelines: How to detect and prevent failures

Introduction

The detection and prevention of vibrations in hydrocarbon pipelines is of utmost importance. It is not only about protecting the physical integrity of the pipelines and associated systems, but also about protecting the environment and the safety of workers and communities. Additionally, uncontrolled vibrations can lead to a decrease in operational efficiency, increase maintenance costs, and reduce equipment life.

Industrial piping systems are subject to failure caused by vibration. To mitigate this risk to integrity, it is important to perform a vibration analysis during the design stage and identify the most critical areas during the operational phase. If vibrations are not adequately detected and controlled, they cause operational and safety problems, ranging from premature component wear to failures such as dangerous leaks or spills.

Causes that generate vibrations in hydrocarbon pipelines

Vibrations in pipes manifest themselves as a complex oscillatory movement that propagates in the form of waves, generating deformations and tensions. These vibrations are caused by various factors, affecting the correct functioning of the pipes. Below are some of the most common:

Deviations from the pipeline design phase often lead to vibration problems. Common standards or codes, such as ASME B31, provide a general framework for piping design without delving into specific vibration analysis for these systems.

Likewise, faulty assembly or installation of the systems, structural integrity defects, including supports and pipe racks, among others, are present as possible causes.

After the commissioning of the pipes, there are causes of vibration, such as high flexibility or insufficient rigidity, excessive loads or resonance problems, causing high vibration amplitudes; where resonance problems arise because the excitation frequency coincides with the natural frequency of the piping system.

Additionally, vibrations vary depending on the load conditions present in the pipe; these may change over time due to changes or improvements in the efficiency of the processes, manifesting vibrations not contemplated or calculated in the design.

Types of vibrations that can occur in piping systems

• Flow Induced Vibrations (FIV): They occur when the fluid flow encounters important discontinuities or changes in direction such as: elbow, tee, reduction, expansion or semi-closed valves, and generate vortices or eddies that interact with the pipe structure. , causing vibrations.
• Acoustically Induced Vibrations (AIV): They are produced by high levels of acoustic energy, typical of high velocity gas systems. This vibration is caused by pressure drop in devices such as: pressure reducers, control valves and relief valves.
• Pulsations of pumps and compressors: These equipment produce fluctuations in the pressure and flow of the fluid, manifesting a rhythmic variation that propagates along the pipe and generates oscillating movements that can resonate with the natural frequency of the pipe. The characteristics of the pulsations depend on the service properties of the pumped fluid, the arrangement of the pipes, the number of pumps, the operating speed, the type and power of the pump.
• Resonance: It is when the natural frequencies of the pipes coincide with the excitation frequencies of the fluid or equipment, a resonance occurs which amplifies the vibrations.
• Mechanical energy of turbomachines: The mechanical energy generated by these equipment is transferred to the system through rotational forces and moments of imbalance; If these forces are not balanced or the pipe is not well supported, vibrations arise. Mechanical energy transmission causes movements in various modes (axial, lateral and torsional) and are especially problematic in long piping systems.
• Water hammer: It is a hydraulic phenomenon produced by rapid changes in the speed of the fluid, such as the abrupt closing of valves or the starting and stopping of pumps. This change generates excessive internal pressure waves, pipe collapse, flange leaks, and large pipe movements.
• Cavitation and flashing: Cavitation is produced by pressure variations, which causes the formation of vapor bubbles that, when imploded, generate pressure waves; This implosion is accompanied by noise and vibrations. For its part, flashing is the rapid change of a liquid to vapor, which generates additional turbulence and vibrations. They are critical anomalies due to the high pressures and velocities involved.

Likewise, there are vibrations due to wear and friction, those generated by thermal movements due to the expansions and contractions of the pipe, due to temperature changes and those caused by external loads such as: wind, earthquakes, or mechanical impacts can induce vibrations. in the pipes. Understanding each of these sources is the first step to developing and implementing the necessary control, mitigation and prevention measures.

Strategies for detecting vibrations in hydrocarbon pipelines

Abnormal vibrations in pipelines are a serious threat to operating systems; Fatigue induced by excess vibrations is one of the most common causes of failure of these systems; An unforeseen leak resulting from undetected vibrations generates economic losses, involving both operational safety, personnel and the environment. These are part of the reasons why companies implement clear strategies to detect vibrations outside the parameters.

Among the most common strategies are:

• Visual Inspection Testing: Although not a quantitative method, because pipeline vibrations are typically low frequency, visual inspection is still a valuable tool for identifying signs of excessive vibration. The programs of visual inspection used as a first step in the vibration evaluation of the piping system; It is carried out by qualified personnel knowledgeable about the facilities, to basically detect: misalignment or deformation of the pipe, misalignment of flanged joints, failures in the integrity of supports, clamps, shock absorbers among other components.
• Portable vibration analyzers: Portable devices equipped with sensors such as accelerometers or speedometers are used to measure vibration levels at various points in the piping system. These analyzers provide real-time data on vibration amplitudes and frequencies.
• Vibration monitoring: It consists of installing permanent sensors in the pipeline for continuous monitoring of real-time conditions of natural vibrations and detects any abnormal behavior, the data from the sensors is used to predict and schedule preventive actions.
• Vibrational spectrum analysis: Uses spectral analysis techniques to decompose vibration signals and study their frequency components. This technique is used to identify specific sources of vibration and evaluate the severity of the problem.
• Pulsation analysis: Evaluates pressure pulsations within the pipeline, which can be a significant source of vibration. Especially relevant in systems with pumps and compressors, where pulsations are normally a problem to monitor.
• Modal analysis and measurement of natural frequencies: This technique involves the identification of the natural vibration frequencies of the pipeline to determine if they coincide with the excitation frequencies of the equipment and processes. Accelerometers and displacement sensors are used to measure vibrations at various points in the pipeline and analyze vibration modes.

Conclusions

Vibrations in hydrocarbon pipelines represent an important problem for this sector, where detecting and preventing failures is necessary for industrial safety and environmental protection. Accurate identification of the causes of vibrations is essential to implement effective control and mitigation strategies.

By considering vibration from design to operation, and employing an integrated methodology that combines visual inspections with advanced technologies, organizations properly manage the integrity and operational efficiency of their piping systems.

References

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