Leak Detection and Repair

Compressed air leaks typically represent 20-30% of consumption in industrial plants. A systematic detection and repair program can significantly reduce energy costs.

Leak Impact

Cost by Leak Size

Based on: 100 PSI, $0.10/kWh, 8,000 h/year, compressor efficiency 18 kW/100 CFM

Orifice Diameter	Leak (CFM)	Annual Cost
1/64" (0.4 mm)	0.2	$26
1/32" (0.8 mm)	0.8	$104
1/16" (1.6 mm)	3.1	$403
1/8" (3.2 mm)	12.4	$1,613
1/4" (6.4 mm)	49.8	$6,474
3/8" (9.5 mm)	112	$14,560

Calculation Formula

$$\text{Annual cost (\$)} = \frac{CFM \times 0.746 \times (kW/100 \text{ CFM}) \times \$/kWh \times \text{hours/year}}{4.0}$$

Detection Methods

Ultrasound

The most effective and practical method for operating plants.

Principle: Leaks generate turbulence that produces ultrasonic sound (20-100 kHz), inaudible but detectable with specialized equipment.

Equipment	Range	Sensitivity	Approx Cost
Basic	38-42 kHz	0.5 CFM @ 3 ft	$1,000-3,000
Intermediate	20-100 kHz	0.1 CFM @ 3 ft	$3,000-8,000
Advanced	20-100 kHz + camera	0.05 CFM @ 10 ft	$15,000-40,000

Advantages:

• Works with plant operating
• Detects small leaks
• No silence required
• Precise location
• Approximate quantification

Procedure:

1. Scan area with detector in search mode
2. When signal detected, approach to locate exactly
3. Use focuser (cone) for precision
4. Mark location with tag
5. Record in database

Soap Solution

Simple method to verify suspected leaks.

Recommended mixture:

• Water: 1 liter
• Liquid soap: 50 ml
• Glycerin (optional): 10 ml (improves bubble formation)

Procedure:

1. Apply solution to suspected connection
2. Observe bubble formation
3. Large bubbles = large leak
4. Continuous small bubbles = small leak

Limitations:

• Requires close access
• Doesn't work in hot areas
• Doesn't quantify leak
• Slow for large inspections

Pressure Decay Test

Quantifies total system leaks when plant is stopped.

Procedure:

1. Pressurize system to normal pressure
2. Shut down compressors
3. Close tank outlet valve
4. Record initial pressure (P1) and time
5. Wait 10-30 minutes
6. Record final pressure (P2) and time

Calculation:

$$\text{Leak rate (CFM)} = \frac{V \times (P_1 - P_2)}{T \times 14.7 \times 1.25}$$

Where:

• $V$ = System volume (cubic feet)
• $P_1, P_2$ = Pressures (PSIG)
• $T$ = Time (minutes)
• $14.7$ = Atmospheric pressure
• $1.25$ = Correction factor

Acoustic Cameras

Emerging technology that visualizes leaks in real time.

Operation: Ultrasonic microphone array generates thermal-acoustic image overlaid on visible image.

Feature	Typical Value
Detection distance	Up to 50 m
Resolution	124 microphones
Frequency	2-65 kHz
Quantification	Automatic (L/min or CFM)

Advantages:

• Very fast inspection
• No close access required
• Automatic visual documentation
• Ideal for hazardous or hard-to-access areas

Common Leak Locations

By Frequency

Location	% of Leaks
Threaded connections	30%
Hoses and quick couplings	25%
Regulators and FRLs	15%
Valves	10%
Cylinders and actuators	10%
Unions and flanges	5%
Other	5%

Critical Points to Inspect

Connections:

• Threaded unions
• Compression fittings
• Quick couplings
• Hose connections

Equipment:

• Pressure regulators
• FRL units
• Solenoid valves
• Pneumatic cylinders
• Rotary actuators

Accessories:

• Pressure gauges
• Drain valves
• Relief valves
• Instrument connections

Leak Management Program

Inspection Frequency

Plant Type	Recommended Frequency
Critical (24/7)	Monthly
Normal industrial	Quarterly
Light use	Semi-annually

Documentation

Each detected leak should be recorded:

Field	Example
Unique ID	LEAK-2024-0147
Detection date	2024-03-15
Location	Line 3, Machine 12, FRL
Component type	Regulator
Estimated size	2 CFM
Estimated annual cost	$260
Priority	Medium
Repair date	2024-03-22
Action taken	Diaphragm replacement
Verification	Confirmed no leak

Program Metrics

Indicator	Typical Goal
Leaks as % of demand	< 10%
Average repair time	< 7 days
Leaks repaired vs detected	> 90%
Annual leak reduction	5-10%

Leak Repair

By Component Type

Component	Typical Repair
Threaded connection	Disassemble, apply sealant, retighten
Quick coupling	Replace O-rings or complete coupling
Hose	Replace hose
Regulator	Replace diaphragm or unit
Solenoid valve	Replace seals or valve
Cylinder	Replace seals or repair kit
Pressure gauge	Replace
Automatic drain	Clean or replace

Thread Sealants

Product	Application
PTFE tape	Standard NPT threads
Paste with PTFE	Difficult connections, vibrations
Anaerobic sealant	Permanent, high pressure

Correct procedure:

1. Clean threads completely
2. Apply sealant only on male thread
3. Leave 2 threads free at tip
4. Tighten firmly but don't overtighten
5. Verify with detector or soap

Repair Prioritization

Priority	Criterion	Action
Critical	> 10 CFM, safety	Immediate
High	5-10 CFM	< 24 hours
Medium	1-5 CFM	< 7 days
Low	< 1 CFM	Next maintenance

Return on Investment

Example Calculation

Typical plant:

• Installed capacity: 500 CFM
• Energy cost: $0.10/kWh
• Operation: 8,000 h/year
• Estimated leaks: 25% (125 CFM)

Program investment:

• Ultrasonic detector: $5,000
• Training: $2,000
• Inspection time: $3,000/year
• Repair materials: $2,000/year
• First year total: $12,000

Savings:

• Current leak cost: $16,250/year
• Reduction goal: 80%
• Annual savings: $13,000

First year ROI: 108% Payback: 11 months

Leak Prevention

Best Practices

Practice	Benefit
Use quality couplings	Lower failure rate
Specified torque on connections	Prevents damage and leaks
Hoses with protection	Longer service life
Automatic drains	Prevents corrosion
Adequate filtration	Protects components
Optimal pressure	Less stress on seals

Design to Minimize Leaks

• Minimize number of connections
• Use welding where possible
• Install shutoff valves by zones
• Design for easy access and inspection
• Specify quality components