Pressure vessels are industrial containers designed to hold vapors, liquids, or gases under specific pressure conditions. These vessels are essential in various industries, from energy production to chemical processing, and their safe operation is crucial for both personnel and equipment.

Given the high-pressure environments they operate in, pressure vessels can be hazardous if not properly maintained. Regular inspections play a vital role in ensuring these systems remain safe and functional over time, helping to identify potential issues before they escalate into serious problems.

This article explores what pressure vessels are, the importance of inspections, common questions about them, and how modern technology like drones is revolutionizing the inspection process.

What is a Pressure Vessel?

Although we’ve briefly defined pressure vessels at the start of this article as “containers designed to hold vapors, liquids, or gases at a specific pressure,” it's important to understand that each country has its own legal definition. This variation underscores the need for careful consideration when dealing with such critical equipment.

The strict definitions exist because pressure vessels pose significant risks. If improperly handled, they can lead to catastrophic failures, which may result in explosions, fires, or dangerous gas leaks. To mitigate these risks, every country has regulations governing the design, construction, and operation of pressure vessels.

Each pressure vessel also has specific operating parameters—known as design pressure and design temperature—that must be strictly followed. Operating beyond these limits could lead to severe consequences, including structural failure and safety hazards.

Understanding the design and operational constraints of a pressure vessel is essential for anyone involved in its use, maintenance, or inspection.

Common Characteristics of Pressure Vessels

Pressure vessels share several key characteristics that make them suitable for high-pressure applications:

• Shape: The most common shapes are cylinders, cones, and spheres, chosen for their structural efficiency and strength.
• Design: The design of a pressure vessel is influenced by the volume it holds and the pressure it must withstand. Stronger materials allow for lighter designs.
• Construction Materials: Steel is the most commonly used material due to its strength, but composites and reinforced concrete are also employed in certain applications.
• Corrosion Resistance: Materials must be selected based on the environment and the substances they will contain to prevent degradation over time.
• Pressure: Most pressure vessels are designed to operate at 15 psig (pounds per square inch gauge) or higher.

Psig measures the pressure above atmospheric pressure. Understanding this concept is important for proper vessel operation and safety.

Types of Pressure Vessels

There are many types of pressure vessels, each serving different purposes in industrial settings:

• Storage Tanks/Vessels: Used to store liquids, often made of carbon steel and available in various sizes.
• Boilers: Designed to produce steam or hot water, typically made of alloyed steel to withstand high temperatures and pressures.
• Heat Exchangers: Used to transfer heat between fluids, often made of carbon steel for durability and efficiency.
• Process Vessels: Used in chemical or manufacturing processes to mix, separate, or treat materials.

Safety Considerations in Pressure Vessel Design

Given the inherent risks, safety is a top priority in pressure vessel design. Two key safety features include:

• Safety Valves: These release excess pressure to prevent overpressurization, reducing the risk of explosion or rupture.
• Leak Before Burst: A design feature that ensures the vessel will leak rather than explode, allowing for safer pressure release in case of failure.

Pressure Vessel Inspections

Regular inspections are a critical part of maintaining the integrity and safety of pressure vessels. This section covers the frequency of inspections, what they involve, and the types of testing used.

The Elios 2 collects visual data during a pressure vessel inspection

Frequency of Inspections

Most regulatory bodies require pressure vessels to be inspected at least once every five years. Additional inspections are needed after installation and before the vessel is put into service.

What Is Done During an Inspection

Inspections typically involve checking the external and internal condition of the vessel, measuring thickness, analyzing stress, and testing pressure release valves. Hydrostatic tests are also performed to verify the vessel’s integrity.

Types of Pressure Vessel Testing

Five common non-destructive testing methods are used during inspections:

1. Visual Testing

Inspectors visually examine the vessel for cracks, corrosion, or other visible defects.

2. Ultrasonic Testing

Uses sound waves to detect internal flaws and measure wall thickness.

3. Radiographic Testing

Uses X-rays to detect internal and surface defects.

4. Magnetic Particle Testing

Identifies surface and near-surface flaws using magnetic fields.

5. Dye Penetrant Testing

Uses a liquid penetrant to reveal surface defects, often under UV light.

Pressure Vessel Inspection Checklist

Here is a list of items typically checked during an inspection:

External Inspections

• Check for defects in insulation and coatings
• Look for signs of leakage
• Inspect mountings for proper expansion and contraction
• Examine the vessel for deformations, cracks, or gouges
• Check for corrosion on nuts, bolts, and flanges
• Inspect shell surfaces and heads for bulges or blisters
• Review welded joints for cracks or defects

Internal Inspections

• Check for cracks, corrosion, or deformation inside the vessel
• Ensure threaded connections have sufficient engagement
• Verify that openings are free from obstructions
• Inspect special closures for adequacy
• Look for cracks or wear in high-stress areas

A printable checklist can help streamline the inspection process and ensure nothing is missed.

Common Questions About Pressure Vessels

Below are answers to some frequently asked questions about pressure vessels:

• At what pressure does a vessel become a pressure vessel?
• What is the difference between an unfired and a fired pressure vessel?
• What regulatory bodies oversee pressure vessels?
• What are the global pressure vessel standards?

At What Pressure Does a Vessel Become a Pressure Vessel?

Typically, a vessel is classified as a pressure vessel if it operates at 15 psig or higher. This threshold varies slightly by jurisdiction, but it serves as a general guideline.

What Is the Difference Between an Unfired and a Fired Pressure Vessel?

An unfired pressure vessel is not directly heated, while a fired one is. Fired vessels require additional safety measures due to the risk of overheating and subsequent failure.

What Regulatory Bodies Oversee Pressure Vessels?

Regulatory oversight varies by country, but common standards include the ASME Boiler and Pressure Vessel Code in North America and the European Pressure Equipment Directive.

What Are the Pressure Vessel Standards Around the World?

Standards include ASME Section VIII, EN 13445, and AD Merkblätter, among others. These ensure consistency and safety in the design and operation of pressure vessels globally.

Five Ways Drones Can Help with Pressure Vessel Inspections

Drones have become a game-changer in the inspection of pressure vessels. They allow inspectors to gather visual data without entering confined or hazardous spaces, improving safety and efficiency.

The Elios 2 drone, for example, is designed to navigate tight spaces safely, making it ideal for inspecting complex structures. Its features include flight stabilization, powerful lighting, and high-quality imaging, all of which enhance the inspection process.

Here are five major benefits of using drones for pressure vessel inspections:

1. Safety

Drones eliminate the need for human entry into potentially dangerous environments, significantly reducing the risk of injury.

2. Cost Savings

Using drones reduces the need for scaffolding and other costly infrastructure, leading to substantial savings for companies.

3. Access

Drones can reach areas that are difficult or impossible for humans to access, providing a more comprehensive inspection.

The Elios 2 inspecting a gas tank

4. Better Data

Drones can collect high-resolution images and video, creating a detailed record of the vessel’s condition for future reference.

5. Environmental Benefits

Increased inspection frequency through drone use can reduce greenhouse gas emissions. For example, a study found that using the Elios 2 could cut CO2 emissions by up to 649 metric tons annually.

 

The Future of Pressure Vessel Inspections

As technology continues to evolve, so too do the methods used to inspect pressure vessels. Emerging trends suggest a growing reliance on remote visual inspection (RVI) tools like drones and advanced sensor technologies.

The Growing Adoption of Drones

Drones are becoming increasingly popular for pressure vessel inspections due to their ability to quickly and safely access hard-to-reach areas. Their use not only improves safety but also enhances efficiency and reduces costs.

With the ability to conduct inspections more frequently, companies can maintain better control over the condition of their equipment, leading to improved long-term performance and reduced downtime.

Recent Technological Advances May Diversify Drone Use Cases

New technologies, such as SLAM (Simultaneous Localization and Mapping), enable drones to create real-time 3D maps, allowing for more precise navigation and defect identification. Combined with advanced sensors, drones can now provide detailed data on everything from temperature to gas leaks.

Software advancements also support faster data analysis, enabling inspectors to make informed decisions more quickly. As these technologies continue to develop, the future of pressure vessel inspections looks more efficient, accurate, and safe than ever before.

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