Pressure vessels are used and relied upon every day in applications all around the world. But first, what are they? In its simplest form, a vessel is a closed container that is engineered to hold gases or liquids at a significantly higher or lower pressure than the ambient atmosphere. The most basic example of a pressure vessel could be something like a compressed air canister. On the more advanced end of things vessels can be found in experimental laboratories everywhere, as well as in space shuttle living environments.

However, while the design and engineering used to produce vessels is incredibly important in the way they function and reliably do their job - safety is equally (if not more) critical.

Due to the pressure differential that takes place within a vessel, dangerous and fatal accidents have occurred throughout their history around the world. Because of this, they are now designed, manufactured, and operated according to a strict set of rules, backed by legislation. While standards tend to change from country to country, they all involve restrictions for values such as temperature and the maximum operating pressure.

For hundreds of years, controlling and containing various substances under pressure has been absolutely essential for industries everywhere. However, the operative word here is indeed "controlling". Proper control of very dangerous pressure differentials is pivotal when it comes to avoiding potentially fatal accidents that can occur due to improper vessel engineering and operation.

For the most part, the widespread industrial usage of pressure vessels saw its genesis with the proliferation of steam power during the industrial revolution in Great Britain. During this time, industrialists took advantage of the pressurized water and steam to power steam engines that were used for everything from trains to manufacturing equipment.

However, according to the American Society of Mechanical Engineers - the governing body that dictates pressure vessel standards - the quick rise of steam power came with its own problems. Due to the technology being relatively new and untested, secure fittings, valves, and boilers at sea and on land "were exploding with terrifying frequency." Despite engineers in America making major breakthroughs when it came to industrialization, poorly implemented vessels killed 50,000 and injured two million men and women every year.

This was some of the first measurable data that pointed towards the necessity for new and stringent pressure vessel standards. As standards for vessel safety became more prevalent, the technology continued to grow to where it is today. Modern applications that rely on pressure vessels range from domestic hot water storage to highly advanced applications such as nuclear reactors, submarines, space ships, and storage containers for gases ranging from chlorine to ammonia. With the many applications that take advantage of pressure vessels in mind, a number of modern inspection techniques have been pioneered.

Primary among modern pressure vessel testing techniques is online inspection. Online inspection typically involves testing the thickness of the metal in vital areas, on a regular basis. This is done to measure the health of the pressure vessel, and monitor when it reaches a minimum thickness for the pressure vessel's application. Once this point is reached, repairs must be made to the vessel to prevent failure.