Leaks: a costly problem

Michael Strobel, Swagelok Company, USA, identifies common causes and costs of fluid system leaks, and outlines methods to prevent them.

Fluid system leaks are a frequently occurring problem in many industrial facilities. Their commonality, however, does not make them less problematic. Even the smallest leak can compromise a plant’s safety and profi tability. To best defend against leaks, it is helpful to understand how and why leaks occur, how to locate and test for them, and how to develop a strategy to address and reduce leaks plantwide.

This article will review common causes of leaks, appropriate methods for identifying them, and proactive strategies for reducing leaks across a facility.

A costly problem

Across a given industrial facility, fl uid system leaks can contribute to a wide range of preventable costs, including the following: Unplanned downtime: plants lose valuable production output potential every time they shut down a process to fix a leak. This downtime can result in significant profit loss. Off-spec production: leaks may lead to the inadvertent production of an off-spec product. This material must then be reworked, sold at a reduced price, or discarded. Damaged equipment: leaking lubricants can lead to premature wear on critical equipment and, in some cases, total machine failure. Hydraulic fluid leaks: it is estimated that millions of gallons of hydraulic fluids are wasted each year.

A single gallon of hydraulic fluid averages US$40. Slips and trips: fluid leaks can pool on the plant floor, contributing to an unsafe work environment where personnel may slip or trip. Non-compliance fines: leaks can lead to significant fees or fines for non-compliance if systems and equipment violate safety regulations. In addition to fees or fines, fugitive emissions can be expensive to repair and dangerous to the health of employees. Time and labour costs: locating and repairing leaks requires time and money. In certain instances, a special team may be necessary to manage toxic chemical leaks, potentially leading to the exorbitant cost of shutting down a system for a thorough inspection.

The most effective way to reduce these unnecessary costs is to quickly identify and repair leaks already occurring and, more importantly, to prevent leaks before they happen.

Figure 1. Use a gap inspection gauge to ensure sufficient tightening of a fitting. If the gauge will not enter the gap between the nut and fitting body (left), the fitting is sufficiently tightened. If it will (right), additional tightening is required.

Figure 2. A real leak involves a system fluid escaping via cracks or gaps between sealing surfaces.

Identifying common leak causes

How do leaks occur? Individual fluid system components themselves are typically not to blame. Rather, human error that occurs during the selection, specification, or installation process is the most common culprit.

Choosing the right components and installing them correctly can reduce the frequency of leaks, helping to enhance plant safety and save significant cost. To better understand and reduce leaks throughout a facility, it is helpful to understand these three common causes of leaks:

Improper tube fitting installation

Tube fittings that have been improperly installed can lead to poor performance. It is important to ensure that technicians know how to properly make up a fitting, including proper ferrule orientation and appropriate use of a gap inspection gauge (Figure 1) to verify the correct amount of pull-up.

Unreliable metal-to-metal seals

Maintaining reliable metal-to-metal seals can be challenging over the long-term. It is important to follow manufacturer guidelines precisely to avoid leaks when using these types of seals. In some cases, as with valves, it may be necessary to replace a metal-to-metal seal with one featuring a soft seat seal. This can be particularly beneficial when repetitive gas shutoff is required.

Poor tubing selection, handling, and preparation

Incorrect tubing selection and improper preparation can further increase the potential for leaks. For example, tubing materials that are incompatible with the process fluid or external environment will be prone to corrosion, premature failure, and therefore, leaks. Poor tube handling or cutting can also impact performance. Dents, scratches, or poor deburring can compromise the fitting’s ability to create a reliable seal.

When building a fluid system, correcting these common mistakes can be an effective way to reduce the likelihood of leaks over the system’s lifetime.

The three most common types of leaks

When leaks do happen, it is important to be able to identify the type of leak so that proper corrective

measures can be taken as soon as possible. The following outlines more information about the three most common forms of leaks:

Real leak

Real leaks (Figure 2) are the result of a pressure barrier’s failure to contain or prevent a system fluid from escaping into the surrounding environment. Real leaks occur due to some form of gap between sealing surfaces or cracks in the material. They are commonly found in valves in which the packing material may have become brittle, cracked, or deformed. Therefore, it can be helpful to use valves that swing open in-line so technicians can make a simple packing replacement instead of needing to uninstall and reinstall (or replace) the entire valve.

Figure 3. A virtual leak releases fluid trapped within a system into other areas of the system.

Figure 4. Within a dead leg, old material trapped in the tee formation becomes a virtual leak into the main fluid stream, resulting in contamination.

Figure 5. Permeation involves fluid that penetrates and moves through and out of a pressure barrier. Virtual leak

A virtual leak (Figure 3) is the release of an internally trapped fl uid into a fl uid system, often resulting from material outgassing, absorbed or adsorbed fl uids, entrapment in crevices, or dead legs (Figure 4).

Permeation

Permeation (Figure 5) is the passage of fl uid 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.

Effectively detecting leaks

Most leak testing is performed while the system is pressurised, either with actual process fl uid or a surrogate (water, air, nitrogen, and helium are common surrogates). Test methods can be broadly segmented into those typically performed on installed equipment, and those more commonly performed on a benchtop or in a laboratory.

Visual testing

Simple visual inspection is an effective way to fi nd leaks in a liquid system, e.g. spotting actual drips or surface wetting below the location of the leak. Visual tests are most commonly performed on installed equipment, but they can also be used for test or benchtop hose assemblies.

Bubble testing

Bubble testing is a simple test for gas systems. It uses a thin fi lm surfactant, soap solution, or submergence in a water bath to identify leaks. If bubbling is observed in the surfactant or in the water bath after pressurisation, this indicates the presence of a leak.

Pressure change testing

Pressure change testing is performed by pressurising equipment in isolation at a certain pressure for a certain length of time. Leakage is indicated by a gradual, measurable drop in pressure. Pressure change testing is common in benchtop applications, but it can be used on installed equipment with careful considerations.

Airborne ultrasonic testing

This type of test can only be used on gas systems and requires an airborne ultrasonic measurement device to locate the presence of a leak. It can be used to approximate the rate of leakage for pressurised systems, and is therefore common on installed equipment. It can also be performed on unpressurised systems, assuming an ultrasonic transmitter can be placed inside the system to be tested.

Mass spectrometry testing

This test uses a mass spectrometer to detect the presence of trace amounts of leaks in gas systems and can help quantify the leakage. Outboard testing is used for pressurised systems, while inboard testing is used on vacuum systems. This method is most commonly used on a benchtop to identify very small leaks.

Prioritising fixes

After identifying leaks in a plant, it is not often possible to fi x all of them straightaway. Instead, leaks should be categorised as follows to prioritise repairs:

Dangerous leaks

Any leak that presents a safety hazard requires immediate attention. This includes noxious gas and caustic chemical leaks, as well as leaks that create slip/fall hazards.

Costly leaks

Collectively, all the leaks in a plant may add up to a signifi cant cost. However, even small leaks can be responsible for a signifi cant percentage of that cost. Fixing a small leak of expensive argon gas, for example, may offer drastically greater savings compared with stopping a large leak – or even numerous small leaks – of cheaper compressed air.

Nuisance leaks

There may also be a variety of minor leaks that do not compromise safety or lead to major costs. These low-priority leaks can be addressed when it is convenient.

Real world impacts

The impact that leaks can have on a plant’s bottom line is observable in a recent project undertaken by a large petrochemical producer operating in Texas, US. Faced with rising utility costs, the producer wanted to review its consumption of utility gases. The producer purchases compressed air and nitrogen from an adjacent plant using ‘pay meters’ under an agreement that is based on a minimum/maximum quantity model. If the usage exceeds the maximum level, the adjacent plant charges a higher rate. This was unfortunately a regular occurrence.

With the help of Swagelok Texas Mid-Coast, the producer evaluated its utility gas systems, which had largely gone unchecked for years. The team audited the utility gas systems for six units and then provided a detailed analysis that enabled the petrochemical producer to see the locations of leaks, their severity, and the potential payback opportunity if the facility were to correct each leak. From there, the company could prioritise and plan fi xes that could result in major potential annual estimated cost savings from the often-overlooked leaks.

To date, with just a fourth of the customer’s units evaluated, Swagelok has found a combined savings opportunity of close to US$500 000/yr. As repairs were completed, the petrochemical producer also noticed an ancillary benefi t – it was able to reduce the size of its permanent compressor rentals and may be able to potentially eliminate them all together. This will result in signifi cant additional cost savings.

The project is indicative of the impact leaks can have on an operation and its expenses. For hydrocarbon facility operators, examining critical systems for leaks can lead to major benefi ts.