1.
Industrial Boilers Need Regular Servicing
2.
Industrial Boiler Inspection Requirements
2.1.
Boiler Inspection Intervals
3.
Recommended Boiler Inspection Methods
3.1.
Ultrasonic Testing (UT)
3.2.
Acoustic Emission Testing
3.3.
Eddy Current Testing (ECT)
3.4.
Liquid penetrant testing (PT)
Around the first century, Heron of Alexandria invented the Aeopile — a small boiler that generated steam, rotating the attached sphere. Although impressive for the time, the early prototype had little utility.
The first residential and industrial boilers didn’t appear until the 17th century. Although small in capacity, low-pressure (around 5 psi), and coil-fueled, first boilers managed to later spur the Great Industrial Revolution.
Fast forward to today, boilers have evolved into highly powerful machines that can deliver pressures as high as 4500 psi. Yet greater operating capacities and more intricate design come at the cost of more challenging maintenance. That’s where non-destructive testing, particularly assisted by drones, comes in handy for checking your equipment from inside and out, without disrupting operations.
Nearly every industry relies on boilers for energy generation. In 2023, Michelin spent $50M on a facility equipped with natural gas boilers. Later that year, Göteborg Energi launched an impressive €217.7m project to integrate their power plant with a new biomass boiler. Finally, Klabin just invested $1.7 billion to upgrade their paper mill, adding a new recovery boiler.
Yet, spending hardly ends with the facility construction. Due to combustible contents, high temperatures, and extreme pressures, boilers are prone to overheating, daily wear and tear, and a decrease in efficiency over time. And thus require regular maintenance and period upgrades.
Lack of therefore can have devastating consequences. According to the US OSHA database, 2-15 deaths and injuries occur each year due to boiler explosions, steam overflows, and pressure releases. Meanwhile, a UK-backed study found that hydrogen boilers cause 65 injuries per year, and gas boilers – 17.
Timely servicing of industrial boilers is crucial for accident prevention — and there are other reasons for regular servicing:
All aspects of boiler operations are regulated – from design and construction to servicing and repairs. Standards require periodic inspections (including internal, external, and NDT) by certified personnel, using standardized procedures and approved tools.
Generally, you’ll need to check the boiler’s heating systems, venting systems, pressure vessels, tubes, pipelines, and gas valves for internal corrosion, blockages, and waste. Also, examine the continuity of the electrical connections and wiring. Visually check the exteriors for bulging, signs of verdigris, rust, stress cracking, and leaks. Measure water pH levels to ensure it’s in the proper range. Finally, check how well screw threads attach to all fittings and mounts.
More precise requirements will largely depend on your local laws, boiler type/capacity, and manufacturer recommendations. Internationally, there are two core standards:
Standards also differ from country to country, and in the United States – from state to state. For instance, Boiler Test Code 2018 operates in the United Kingdom. The standard describes requirements for inspections of copper and steel boilers from 3 to 1100 bar liters, recommending ultrasonic testing, x-ray, dye penetration, and magnetic particle inspections
In the USA, there are OSHA 1926.29 and NFPA 85. The standards describe workflows for safe installation, inspection, and testing of boilers and tell how to prevent explosions and implosions.
The intervals between boiler inspections also vary depending on standards, local regulations, and manufacturer recommendations. Here’s the breakdown:
| Type of boiler | Type of inspection mentioned | Standard | Interval |
| Endplate attachment welds in shell boilers | Ultrasonic testing (UT) | SAFed SBG-1 (UK) | Every 5 years |
| Boilers with welds in set-in endplates | UT | SAFed SBG-1 (UK) | Every 5 years |
| Boilers with excessive corrosion, grooving, loss of water, overheating | NDT testing (mostly UT) | SAFed SBG-1 (UK) | Immediately |
| All boiler elements | External and internal | Boiler Test Code 2018 (UK) | Every 7 to 10 years |
| High-pressure boilers | Internal and external inspection | Detroit City Mechanical Code (USA) | Annually |
| Wood-fired boilers | Combustion efficiency testing | Vermont DEC (USA) | Every 2 years |
| All steam boilers | Internal and external inspection | DC Mechanical Code (USA) | Annually |
| High-pressure boilers | Internal inspection | Office of the Illinois State Fire Marshal (USA) | Annually |
| High-pressure boilers | Internal and external | TÜV SÜD | Annually |
Although necessary, boiler inspections can be challenging. Large industrial boilers, together with their steam lines, exhausts, and storage tanks, can reach as high as multistory buildings and need additional access equipment.
Internal inspections are even more difficult. You need to drain the boiler, cool the surface, prevent steam leakage, close all valves, disconnect blow-off lines, and open all vents. That means shutdowns and downtimes. Considering that modern industrial boilers have a capacity of 10M – 40M Btu/hr or even 100M Btu/hr, the shutdown can disrupt the entire facility operation.
That’s where NDT testing, particularly with drones, can help. NDT methods are non-invasive and provide rich asset conditioning data to ensure effective operations and compliance.
Ultrasonic testing is an NDT technique that relies on high-frequency sound waves to measure wall thickness and locate subsurface defects. UT is the most commonly used inspection method for boilers, mentioned in virtually any related standard. Why?
UT is relatively easy to execute, safe for inspectors, and allows testing of immovable objects using just one side. It detects cracks, voids, inclusions, and corrosions of up to 0.05 mm, additionally giving insight into their size, shape, and location. However, UT can’t deliver reliable data if applied to porous, non-homogeneous, or dirty surfaces.
As per the ASME Boiler and Pressure Vessel Code (BPVC), Section V, ultrasonic wall thickness measurement detects the following:
With the Voliro T drone, you can perform UT of massive boilers at height or internally in confined spaces. With live A-scan, you will receive inspection results immediately in the app. Voliro’s UT probe boasts 2 – 150 mm / 0.08 – 5.9 in thickness range, catching corrosion and material degradation at early stages.
For heated boilers, we have a high-temp UT thickness gauge, capable of testing boilers at 0 – 260 °C / 32 – 500 °F of operating temperatures. Even in extreme environments, the probe delivers the same thickness range and resolution as its low-temp counterpart.
Acoustic emission testing (AET) is a method that measures elastic waves resulting from external pressure, load, and temperature applied to an object. These waves make the boiler or its components vibrate. AET converts vibrations into electrical signals that we can further interpret to identify defects.
AET is an effective method for differentiating between developing and stagnant defects. Modern AET probes can penetrate dirt and protective coatings, eliminating the need for extra preparation. However, AET cannot be applied to thick metallic structures (above 20 mm). External factors can also affect the results making them less accurate.
The ASME BPVC, Section VIII, Division 2 requires acoustic emission testing during a hydrostatic test or pneumatic test. AET helps detect:
Eddy current testing (ECT) is a technique that relies on electromagnetic induction to find corrosion, cracks, and material thinning in conductive materials. It’s used mainly to detect near-surface irregularities and measure coating thickness.
ECT requires minimal preparation and covers large test areas in one go – so inspections are much faster than with other methods. The probe doesn’t require direct surface contact. However, the inspection results might be affected by surface characteristics such as roughness, finish, and coating application.
According to ASME BPVC, Section V, eddy current testing detects the following issues in boilers:
Voliro T, mounted with our PEC probe, can reliably detect corrosion under insulation at height. Through the use of short, high-energy electromagnetic pulses, the PEC probe penetrates as much as 100 mm of insulation thickness and provides 3 – 18 mm of wall thickness measurements.
Liquid penetrant testing (PT) is an NDT method that uses colored or fluorescent liquid that seeps into surface-level defects and thus visualizes their layout.
This NDT method is low-cost and easy to perform – no need for complex equipment, only an aerosol can, lamp, and cleaner. PT works for most nonporous materials (in the case of boilers, steel, cast iron, aluminum, and brass). The main drawback is that the examiner must have direct access to the surface. That usually means you will need to cool, clean, and air out the boiler.
According to PG-25.2.1.2.2, boilers need liquid penetrant for all casting surfaces after heat treatment. The NBIC recommends PT find leakage around tubes, inspect weld joints, and evaluate fire-damaged components and fiber-reinforced plastic pressure equipment.
As per ASME BPVC, Section V, PT works best for the following boiler defects:
An annual boiler inspection schedule might be challenging to maintain with just human effort. Inspection drones speed up and simplify the process, ensuring the safety of your personnel and the continuous operation of the facility.
What’s more, drones help collect more comprehensive data. With a variety of payloads available, you can capture HD visuals, take UT thickness measurements, monitor gas emissions, and locate the earliest signs of corrosion.
For instance, with just one Voliro drone, you get most of your NDT needs to be covered as you can
Plus with a Voliro subscription, we take care of drone maintenance, recertification, repairs, insurance, and pilot training.
