Ultrasound Inspection Guide: A Beginner-Friendly Introduction

What is ultrasound inspection?

Ultrasound testing is a non-destructive inspection method that uses high-frequency sound (20–100 kHz) for:

• Detecting compressed air and gas leaks
• Mechanical diagnostics (bearings, pumps)
• Electrical inspection (corona discharge, arcing)
• Equipment checks (valves, steam traps)

How does it work?

Operating principle

1. Turbulence and friction generate ultrasound
2. An ultrasonic sensor "hears" these sounds
3. The signal is converted into the audible range
4. The operator interprets the sound and its intensity

Frequency range

Sound type	Frequency	Detection
Audio	20 Hz – 20 kHz	Human hearing
Ultrasound	20 – 100 kHz	Ultrasound testing

Ultrasound sits above normal background noise, which lets you pinpoint problems precisely.

The 8 pillars of ultrasound testing

SDT identifies 8 core applications:

1. Mechanical monitoring {: style="max-height: 40px; width: auto;"}

Detects: Bearings, gears, pumps, fans

Method:

• Contact sensor on the housing
• Listen for changes in sound
• Compare against a baseline or reference

Indicators:

• Smooth humming = Normal
• Grinding/rattling = Defect
• Increased intensity = Worsening

2. Bearing lubrication {: style="max-height: 40px; width: auto;"}

Problem: Over-lubrication is just as harmful as under-lubrication

Solution: LUBExpert or the manual method

Method:

1. Measure before lubrication
2. Lubricate while listening
3. Stop at the optimal level
4. Verify afterwards

3. Compressed air leaks {: style="max-height: 40px; width: auto;"}

Leak types:

• Connection leaks
• Valve leaks
• Seal leaks
• Hose ruptures

Method:

• Scan the area with an airborne sensor
• Follow the sound to its source
• Tag and document
• Calculate the loss

4. Electrical faults {: style="max-height: 40px; width: auto;"}

Detects:

Type	Ultrasound Signature
Corona	Steady, continuous buzzing
Tracking	Intermittent cracking
Arcing	Loud, irregular pops

Safety: Scan from a safe distance!

5. Steam traps {: style="max-height: 40px; width: auto;"}

Conditions:

Condition	Sound	Temperature Δ
Working	Intermittent click	Hot inlet, warm outlet
Failed Open	Continuous steam	Same temp both sides
Failed Closed	Silence	Cold outlet

6. Hydraulic systems {: style="max-height: 40px; width: auto;"}

Detects:

• Fluid leaks in valves and cylinders
• Internal bypass
• Cavitation

Equipment: Same detectors as for air leaks

7. Valves {: style="max-height: 40px; width: auto;"}

Types of valves checked:

• Control valves
• Safety relief valves
• Check valves
• Solenoid valves

Method:

• Upstream/downstream comparison
• Listen for internal leakage
• Verify proper operation

8. Tightness testing {: style="max-height: 40px; width: auto;"}

Applications:

• Ship hatch covers
• Bulk storage tanks
• Clean rooms
• Pharmaceutical isolators

Method: Ultrasound transmitter + receiver

Equipment

Entry Level: SDT200

Features:

• Basic ultrasound detection
• Headphones for listening
• Analog output
• Simple, intuitive

Best for:

• Leak surveys
• Basic inspections
• Training

Mid Level: SDT270

Features:

• Digital recording
• FFT spectrum
• Data logging
• SD card expansion
• UAS3 compatible

Best for:

• Data collection
• Trend analysis
• Documentation

Advanced: SDT340

Features:

• Multiple sensors (US + vibration)
• Built-in IR thermometer
• Tachometer
• Bluetooth HD headphones
• focUS Mode (up to 256 kHz)

Best for:

• Comprehensive PdM programs
• Complex diagnostics
• Multi-parameter monitoring

Inspection methodology

Pre-Inspection

1. Plan your route — know what to inspect
2. Charge equipment — make sure batteries are ready
3. Check settings — verify sensitivity
4. Review history — check previous findings

During Inspection

1. Scan systematically — follow your route
2. Listen carefully — train your ear
3. Document findings — note all issues
4. Tag problems — mark for follow-up

Post-Inspection

1. Download data — transfer to software
2. Analyze trends — compare with previous readings
3. Generate reports — communicate findings
4. Plan actions — schedule repairs

Interpreting sounds

Common sounds

Sound	Indication
Smooth rushing	Normal turbulence
Intermittent clicks	Working steam trap
Continuous hissing	Leak
Buzzing	Electrical corona
Cracking	Electrical tracking
Grinding	Mechanical wear
Rattling	Loose component

Training tips

1. Start simple — learn obvious leaks first
2. Build a library — record reference sounds
3. Compare similar — compare like-for-like machines
4. Use the spectrum — FFT helps you visualize
5. Get certified — formal training helps

Building a program

Phase 1: Assessment (Month 1)

• Baseline survey
• Identify critical equipment
• Set priorities
• Calculate potential savings

Phase 2: Pilot (Months 2–3)

• Select a pilot area
• Train the team
• Implement routine inspections
• Document results

Phase 3: Rollout (Months 4–12)

• Expand to other areas
• Integrate with your CMMS
• Standardize procedures
• Continuous improvement

Phase 4: Optimization (Year 2+)

• Add permanent monitoring
• Advanced diagnostics
• Predictive analytics
• Industry best practices

ROI calculator

Typical savings

Application	Avg. Savings	Payback
Leak Detection	$15,000/100 traps	<3 months
Bearing Lubrication	50% grease reduction	<6 months
Steam Traps	$2,000/trap/year	<2 months
Mechanical	Prevent 1 failure/year	Immediate

Investment range

• SDT200: $3,000–5,000
• SDT270: $8,000–12,000
• SDT340: $15,000–20,000
• LUBExpert: $10,000–15,000
• Software: $2,000–5,000

Typical ROI: 3–12 months

Resources

Training

• SDT Level 1 Certification
• SDT Level 2 Certification
• Online courses
• On-site training

Software

• UAS3 — data management
• LEAKReporter — leak surveys
• SHERLOGReporter — hatch testing

Standards

• ISO 17359 — Condition monitoring
• ISO 18436-8 — Ultrasound testing

Conclusion

Ultrasound inspection is a versatile, cost-effective tool for predictive maintenance. Starting simple (SDT200) and progressing (SDT270/340) lets you build a comprehensive program.

Key success factors:

1. Proper training
2. Consistent methodology
3. Data documentation
4. Management support
5. Continuous improvement

Ready to start? Contact us for a consultation!