# Comprehensive Compressed Air Leak Detection Checklist May 2006

1.  **Why would an industrial facility want to establish a leak
    remediation program?**

> Compressed air leaks present the most obvious and often neglected
> opportunities to reduce energy consumption. Oftentimes, industrial
> facility staff does not realize the cost and savings opportunities
> associated with leaks. At times, it is not uncommon for facilities to
> have leakage rates in the range of 20 to 30 percent of the compressed
> air that is generated. When reducing leakage, it is best to
> proportionately ensure compressors are controlled properly -- this
> will reduce the energy consumption. Without controls, energy savings
> associated with leak repair may not be reflected on the power bill.

2.  **What are the two types of programs?**

> There are two basic types of leak remediation programs, the "leak tag"
> program and the "seek-and-repair" program. The "seek-and-repair" is
> the simplest -- you simply find the leak and repair it immediately.
> With the "leak tag" program, you identify the leak with a tag and log
> it for repair at a later time. The tag is often a two-part tag: one
> part stays on the leak and the other part is turned in to the
> maintenance department, identifying the location, size, and
> description of the leak to be repaired. The best approach depends on
> the size, type and culture/work practices of the facility. Often the
> best solution is a combination of the two programs.

3.  **How can an industrial facility establish a leak detection
    program?**

> During break or shift change, the compressed air system is delivering
> air to supply leaks. Take advantage of this time to listen for and
> identify leaks. On some compressors with percent capacity gauges, you
> can estimate the amount of leak loads. By being proactive in leak
> detection and repair, a leak detection program can keep facility leaks
> to less than 10 percent of total compressor(s) air flow capacity.
> Reducing air leaks increases the net air delivery capacity of the
> existing compressors. *Note: A good compressed air system leak repair
> program is very important in maintaining the efficiency, reliability,
> stability, and cost-effectiveness of any compressed air system.*

4.  **What are the key elements to a successful leak remediation
    program?**

    a.  Establish a baseline of compressed air usage. Set up a good
        ground for comparison on the effectiveness of the compressed air
        leak repair program.

    b.  Establish leak loss. (See question \# 11 &12 below.)

    c.  Develop an estimated cost for the air leaks. (See question \# 6
        below.)

    d.  Identify leaks. Survey the facility and identify the leaks.
        Leaks can be identified by many methods, but the most common is
        using an ultrasonic acoustic leak detector. (See question \# 10,
        13 & 14 below.)

    e.  Document the leaks. Document the location and type of each leak,
        its size and its estimated cost. Attentively, give a rating
        (small, medium or large) to determine priority. Any
        documentation should be compatible with the facility's
        predictive maintenance program. Leak tags can also be used but
        should not take the place of a master leak list. If you are
        using the "seek-and-repair" methods, leaks should be documented
        so the number and effectiveness of the program can be tracked.

    f.  Prioritize the leak repair. Fix the biggest leaks first to get
        the biggest savings. This will ensure a good start to the air
        leak repair program.

    g.  Document the repairs. Associating cost savings with leak repair
        demonstrates the effectiveness of the program and the savings
        can be determined. Documenting the repairs and the type of leaks
        can also indicate the equipment that may have a recurring
        problem. If this occurs, the process should be looked at for a
        root cause and a permanent solution should be developed to stop
        the recurring air leak.

    h.  Compare baselines and publish results. By comparing before and
        after, the effectiveness of the program and the savings can be
        determined. Then, tell share the program and the results with
        other facilities. This is very important, since the savings will
        solidify support for the program.

    i.  Start over again. Air leaks continue to occur, so the program
        has to be ongoing. Periodic review should be conducted on the
        system, and the process repeated as necessary to maintain system
        efficiency.

5.  **What else is affected by leaks?**

> Leaks can contribute to other operating losses, such as a drop in
> system pressure causing all air-operated equipment to function less
> efficiently -- which can adversely affect production. Leaks can
> shorten the life of all system equipment, such as the compressor
> package itself and suggest the need to add unnecessary compressor
> capacity. The compressor may have additional maintenance requirements
> and increased unscheduled downtime, due to the increased running time.

6.  **What is the estimated annual cost of leaks?**

> Note: costs are calculated by size using electricity rate of \$0.05
> per kWh, assuming constant operation, and an efficient compressor.
>
> [Size]{.underline} [Cost per Year]{.underline}
>
> 1/16" \$ 523
>
> 1/8" \$2,095
>
> 1/4\" \$8,382

7.  **What are the types of air leaks?**

> There are two types of air leaks, intentional and unintentional. In
> order to maintain system efficiency, both types of air leaks must be
> addressed.

8.  **What are intentional air leaks?**

> Intentional air leaks are the ones that have been designed into the
> system. At times, these leaks are blowing, drying, sparging and other
> operations used in the production process. These intentional air leaks
> have been installed as a quick fix for a production problem or are
> used to cool production staff or equipment.

9.  **What are unintentional air leaks?**

> These leaks cause ongoing maintenance issues and can appear in any
> part of the system. They require an ongoing air leak detection and
> repair program.

10. **Where are the most common leakage areas in a system?**

    a.  Couplings, hoses, tubes and fittings. Tubes and push-to-lock
        fittings are common problems.

    b.  Quick disconnect couplings. O-rings required to complete the
        seal may be missing.

    c.  Filters, regulators, and lubricators (FRLs). Low first cost,
        improperly installed FRLs often leak.

    d.  Open condensate traps. Improperly operating solenoids and dirty
        seals are often problem areas.

    e.  Pipe joints. Missed welds and threaded joints are a common
        problem.

    f.  Control and shutoff valves. Worn packing through the stem can
        cause leaks.

    g.  Point-of-use devices. Old or poorly maintained tools can have
        internal leaks.

    h.  Flanges. Missed welds are a common problem.

    i.  Cylinder rod packing. Worn packaging materials can cause leaks.

    j.  Thread sealants. Incorrect and/or improperly applied thread
        sealants can cause leaks. Use the highest quality materials and
        apply them per the instructions.

11. **How do you estimate leak load for systems with load and unload
    controls?**

> The easiest ways to estimate the amount of leakage in the system is to
> start the compressor when there are no demands on the system and bring
> the system to normal operating pressure. All air-operated endues
> equipment should have the supply valves and/or solenoids open to
> account for internal leaks. Any open blowing applications that are
> part of the process should be isolated through shutoff valves. A
> number of measurements are taken to determine the average time it
> takes to load and unload the compressor.
>
> The compressor will load and unload because the air leaks will require
> the compressor to cycle on as the pressure drops from the air escaping
> through the leaks. Total leakage (percentage) can be calculated as
> follows:
>
> Leakage (percent) = [T X 100]{.underline}
>
> (T + t)
>
> T = Time fully loaded.
>
> t = Time fully unloaded.
>
> Leakage will be expressed in terms of the percentage of compressor
> capacity lost. The percentage lost to leakage should be less than 10
> percent in a well-maintained system. Poorly maintained systems can
> have losses as high as 20 to 40 percent of air capacity and power.
>
> *Note: All data should be compared to the original baseline and prior
> readings. Many rotary screw compressors have the capability and option
> to operate in load/unload control. However, because the compressor
> then operates at full capacity when loaded, it is important to check
> that operation at the proposed unload pressure set point will not
> overload the main drive motor.*

12. **How do you estimate leak load for systems with other controls?**

> If there is a pressure gauge downstream of the receiver, leakage can
> be estimated in the system. This will require an estimate of total
> system volume, including any downstream secondary air receivers, air
> mains, and piping (V, in cubic feet). The system is then started and
> brought to the normal operating pressure (P~1~) and the compressor is
> turned off. (Note: the plant should be in the same operating condition
> as \# 11.)
>
> Measurements should then be taken of the time (T) it takes for the
> system to drop to a lower pressure (P~2~), which should be a point
> equal to about one-half the operating pressure. Leakage can be
> calculated as follows:
>
> Leakage (cfm free air) = [V x (P~1~ -- P~2~)]{.underline} ~x\ 1.25~
>
> T x 14.7
>
> *V* is in cubic feet.
>
> *P~1~* and *P~2~* are in psig.
>
> *T* is in minutes.
>
> The 1.25 multiplier corrects leakage to normal system pressure,
> allowing for reduced leakage with falling system pressure to 50
> percent of the initial reading. Again, leakage of greater than 10
> percent indicates the system likely can be improved.
>
> *Note: These tests should be carried out at least quarterly as part of
> a regular leak detection and repair program.*

13. **What method is most recommended to locate leaks?**

> The best way to detect leaks is to use an ultrasonic acoustic
> detector, which recognizes high frequency hissing sounds associated
> with air leaks. These portable units consist of directional
> microphones, amplifiers, and audio filters, and usually have either
> visual indicators or earphones to detect the leaks.

14. **What else can you tell me about the ultrasonic leak detection
    equipment?**

> Ultrasonic leak detection is the most versatile form of leak detection
> and is adapted to a variety of leak detection situations. The
> principle is simple, in a pressure or vacuum leak, the leak flows from
> a high pressure laminar flow to a low pressure turbulence, which then
> creates a white noise containing a broad spectrum of sound ranging
> from audible to inaudible frequencies. An ultrasonic sensor focuses in
> on the ultrasonic elements of the noise, which is loudest at the leak
> site.
>
> The advantages of ultrasonic leak detection includes versatility,
> speed, ease of use, the ability to perform tests while the equipment
> is running, and the ability to find a wide variety of leaks ranging
> from mid-to large-sized leaks. They also require a minimum about of
> training and operators often become competent after just 15 minutes of
> training.
>
> Since ultrasound is directional, the signal is loudest as its source.
> An individual can generally scan around the test area and likely home
> in on a leak site and pinpoint its location. It is a fast and very
> accurate method of leak detection.

15. **How can leaks be repaired?**

> Since most leaks occur at joints and connections, stopping them could
> be as easy as tightening a connection or as complex as replacing
> faulty equipment, such as quick disconnect couplings, fittings, pipe
> sections, hoses, joints, drains, and traps.
>
> Once the leaks have been repaired, the compressor control system
> should be re-evaluated to realize the total savings potential.

16. **Can a system leak be reduced, if repair is not feasible at time of
    detection?**

> Lowering the demand air pressure so the differential across an orifice
> or leak lowers the flow, reducing the system pressure, resulting in a
> reduction of the leakage rate. Stabilizing the system header pressure
> at its lowest practical range will then minimize the leakage rate for
> the entire system.

*NOTE: This information was adapted from the "Best Practices for
Compressed Air Systems," 2003*

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