Fluid system leaks are common throughout the miles of tubing, valves and other components that span most industrial plants. Such leaks represent increased operating costs at best and potential safety issues at worst.
Even the smallest leak can present an issue. A simple drip of fluid on a walkway could cause a slip or fall that can become a lost-time accident. A minor release of toxic gas may result in evacuations and costly fines. A trivial bleed of expensive argon gas could drastically affect a plant’s bottom line. These are just some of the many reasons to address leaks quickly and develop a plan to prevent future ones.
To help maintain plant safety and profitability, a plant’s leak mitigation plan should include training personnel about leak detection and prevention. Effective tactics include focusing on how and why leaks occur, how to locate and test for them and how to develop a strategy to address and reduce leaks plantwide.
Recognizing common leak causes
Surprisingly, most leaks occur due to human error, not substandard parts. Errors may be due to the design and installation of a component or even the component choice. Therefore, it is important to select the right components at the outset and install them correctly. To better understand how to choose the right parts, it is helpful to understand the following top three common causes of leaks:
Unreliable metal-to-metal seals. “Packless” metal-to-metal seals are difficult to make and maintain reliably, especially over time. Installers must follow manufacturer’s guidelines precisely to avoid leaks. To enable a more reliable long-term seal, they may want to replace the component with one featuring an adjustable packing
Improperly installed tube fittings. To reduce the likelihood of leaks and enhance plant safety, installers must properly assemble tube fittings. Technicians should be trained in how to make up a fitting by orienting the ferrules properly, tightening the assembly to specifications and using a gap inspection gauge to verify their work (see Figure 1).
Poor tubing selection and preparation. When tubing materials are incompatible with process fluids or the external environment, they will be prone to corrosion, premature failure and leaks. In addition, tubing preparation is critical, as unevenly cut tubing or tubing that has not been deburred may compromise a fitting’s sealing ability.
Understanding leak types
The type of leak will influence a technician’s troubleshooting and repair steps. By understanding the following three most common types of leaks, the technician will be able to determine the appropriate corrective measures to address them:
Real leaks. A leak that results from a pressure barrier failing to contain or isolate a system fluid from the surrounding environment is called a real leak (see Figure 2). Such leaks commonly occur due to cracks or gaps between sealing surfaces. At a minimum, a technician may need to simply tighten a valve packing to correct a real leak. However, it is possible the technician may need to replace valve components, such as the packing or O-rings (see Figure 3), or the valve altogether.
Virtual leaks. Fluid trapped within a system can unintentionally get released into other areas of the fluid system. Such virtual leaks may occur due to material outgassing (i.e., when gas escapes from a material under test in a vacuum) or from fluids that absorb or adsorb into components and later leak out of those components as system concentrations shift (see Figure 4). In addition, fluids may become entrapped in cracks or stuck in deadlegs and then leak into the fluid stream, potentially changing its composition. One strategy for avoiding virtual leaks is to eliminate deadlegs (see Figure 5).
Permeation. Permeation occurs when a fluid passes into, through and out of a pressure barrier that does not have holes large enough to permit more than a small fraction of the molecules to pass through any one hole (see Figure 6). It is a common occurrence when using fluoropolymers for valve seats and seals or flexible hose cores, as fluids or gases can penetrate the polymer surface, migrate through the material and desorb on the other side. The best way to avoid permeation is to choose components featuring sealing materials that mitigate the phenomenon, including harder plastics such as polyether ether ketone (PEEK).
How to detect leaks
Learning how to detect leaks is a key strategy for enhancing worker safety and decreasing operational risks. A good leak detection program will encompass the five primary nondestructive test (NDT) methods, including bubble testing, pressure leak testing, airborne ultrasonic testing, mass spectrometry testing and pressure change measurement testing.
Bubble testing is a quick and easy way to detect and locate gas leaks. During bubble testing, a technician pressurizes a component to create a pressure differential. Next, the technician either immerses the pressurized component in a solution or applies a soapy film to the exterior of the component and watches for leaks, which will be indicated by bubbles. With bubble testing, technicians can evaluate an entire component at once, which can save time. In addition, the test enables technicians to determine whether a leak is a real or virtual leak.
Pressure leak testing is especially helpful for determining the location of a gas or fluid leak. The two techniques that offer the best results are hydrostatic and pneumatic tests. For either test, the operator gradually pressurizes the component with water or air to a specified pressure and then holds that for a predetermined length of time to measure any loss. This test allows operators to evaluate an entire assembly at once to detect leak rates.
Operators perform airborne ultrasonic testing using a handheld device that can sense medium to large leaks. The test is used mainly to locate leaks in compressed air systems and relies on measuring the magnitude of ultrasonic noise produced when fluid or air leaks with enough velocity to cause turbulence. The test is especially helpful for quickly scanning large areas for leaks and for locating leak sources from a distance.
In mass spectrometry testing, a technician first inserts a sealed component or assembly into a pressure chamber and injects tracer gas (usually helium) into the chamber. Next, the operator transfers the component quickly to a mass spectrometer and applies a pressure differential to measure the amount of tracer gas that has penetrated the component or assembly. If the operator detects tracer gas inside the mass spectrometer, the component has a leak.
Pressure change measurement testing is used to calculate and evaluate a leak rate to ensure the amount of leakage is within acceptable limits. It can determine total leakage in a simple, inexpensive manner by following one of four common techniques, which include pressure decay, pressure change absolute, pressure change reference and volume or flow measurement. For example, using the pressure decay technique, operators pressurize a component with air and use a pressure transducer to monitor that pressure. Any pressure drop indicates leakage.
Prioritizing leak maintenance
Leaks are ubiquitous throughout nearly all plants. However, it is not feasible to address every leak right away. Instead, it is helpful to categorize leaks and prioritize which ones to address first, including fixing the following leaks in order:
Dangerous leaks. Any leak that presents a safety issue should be a plant’s top priority. Such leaks may include releases of noxious gases and caustic chemicals or fluid leaks onto floors and walkways that create slip/fall hazards. A plant’s risk managers should identify these safety issues first and then send their top maintenance technicians to fix them right away.
Costly leaks. All the leaks in a plant will collectively add up to a significant loss. However, sometimes the smallest leaks can contribute the most to that loss. For example, a small leak of expensive argon gas should be prioritized even above a large leak of lower cost compressed air. Stopping the more expensive leak first may drastically help the plant’s bottom line. Maintenance technicians can later address the air leak.
Nuisance leaks. Minor leaks that don’t present safety hazards and are not responsible for major losses can be left for later. Such nuisance leaks should not be ignored, but plants often can wait to address these low-priority leaks when their maintenance staff is not facing other more critical duties.
It is helpful to train — and retrain — engineers and technicians in leak detection and prevention to enhance their skills. Training may include educating them on proper material selection, as well as holding hands-on, skill-building courses that cover tube bending and tube fitting installation procedures. By focusing on identifying and stopping leaks, these skilled professionals can help plants realize safer, more cost-effective operations (see Figure 7).
Adding up losses from leaks
Plants waste millions of gallons of fluid each year due to leaks. At roughly $40 for one gallon of hydraulic fluid, for example, those leaks can add up to significant losses. Furthermore, leaks can account for:
- Lost production: Every process shutdown taken to fix a leak reduces a plant’s production output potential.
- Equipment damage: Loss of lubrication can lead to premature wear and machine failure.
- Off-specification product: A plant may inadvertently produce an off-spec product due to improper instrument calibration or operation caused by a leak. That material must be reworked, sold at a reduced price or discarded.
- Degraded work environments: Leaks in traffic areas can cause slip/fall accidents. In addition, fugitive emission leaks can be expensive and dangerous.
- Fines for noncompliance: Costly fines may result from systems and equipment that violate regulations.
- Cleanup needs: Locating and repairing leaks takes time and money and may even require a special team to manage leaks of toxic chemicals. Additionally, a plant may face the cost of shutting down a system to thoroughly clean it following a leak.