Working safely around pressurized vessels doesn’t have to be a high-pressure task

By Safety Management Group

Pressurized vessels are so common on construction sites and in industrial environments that people often don’t pay much attention to them. In simple terms, a pressurized vessel is any kind of closed storage tank or other container that holds liquids or gases at a greater than normal atmospheric pressure.

The air tanks on compressors are one common example, and the tanks of gases that welders use are another. Refineries and chemical plants contain a wide variety of different types of pressurized vessels. If you buy propane by the tank for your home’s gas grill, that’s still another example. No matter what size or shape, the contents are pressurized to increase the amount in the container and/or allow more rapid delivery.

When pressurized tanks are in good shape with all of the correct devices and lines attached to them, they are very safe. But if they’re damaged, cracked, leaking, or otherwise not completely secure, they can present hazards for explosions (and generating shrapnel), fires, and depending upon the contents, poisoning or suffocation.

That’s why people who work with or around pressurized vessels need to be trained in proper operation and be able to spot potential problems. In addition to those who may use the vessels, that includes anyone who installs, maintains, checks, or repairs them. Training should include an explanation of the vessel’s purpose, design, and contents, as well as a thorough understanding of how to use the valves, read any gauges, and transport the vessel itself.

If the vessel stores flammable or toxic liquids or gases, workers need to have a solid understanding of the properties of those liquids or gases, especially the acceptable pressure and temperature levels, as well as what to do if the device begins to leak or shows signs of failure.

Safety devices
Most pressurized vessels work with specific valves and other hardware. Typically, that includes protective devices that can close the vessel if temperature, pressure, or other parameters exceed a certain amount. There may also be some type of warning device that uses light or sound to call attention to a potential problem. Before working with a vessel, workers need to verify that any safety devices are in place and operating correctly. If not, they must be repaired by someone qualified to do so before anyone uses the vessel.

Nearly all pressurized vessels need regular maintenance to function safety and effectively. Companies and contractors should establish regular maintenance programs for the vessel and the systems with which it works. In addition to ensuring that all valves and safety devices are working properly and that there are no leaks, workers should watch for signs of corrosion or other types of wear that could eventually lead to more serious damage or failure.

Regular inspections of pressurized vessels are a critical part of safety and is often required by local laws. Vessels should be thoroughly inspected before they’re put into service, and then at regular intervals, based upon the manufacturer’s guidance and the nature of their use and the environment.

External inspections should focus on seeking visible defects in the vessel itself — such as cracks, gouges, and deformations — and with any coatings used in the application. In addition, mountings, flanges, and similar elements should be examined to verify their integrity and ensure they can accommodate any contraction or expansion during operations. Any signs of potential leakage must be checked thoroughly before the vessel can be used.

There are several different types of internal inspections that may be performed, including:
Visual checks. As the name implies, visual checks involve looking at the interior of the vessel to identify cracks or other flaws that could weaken the vessel. Large vessels may include hatches or manways to allow inspections. Increasing, inspectors are using drones and similar equipment to allow inspections without needing to enter confined spaces.
Penetrants. Special liquids can be sprayed on the vessel’s surface to make cracks and other flaws more evident. Some fluorescent liquids can be used in conjunction with an ultraviolet (UV) light to improve visibility.
Ultrasonic tests. Equipment using sound waves allows precise measurement of the thickness of the vessel’s walls. An advantage of this approach is that it can detect flaws that are not yet visible.
Particle and radiographic tests. Magnetic particles or radiography can be used to make surface defects more visible.

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