Pressure Vessel Testing Through Non Destructive Methods

Pressure vessels play a key role in many industrial businesses, from chemical, petrochemical, oil & gas, refining, pulp and paper, plastics, pharmaceutical, refrigeration, natural gas processing amongst many more.

Pressure vessels are not to be confused with storage tanks, which are often performing a similar role, however, they're not storing liquid or gas at a pressure far enough removed from the local pressure to be considered a pressure vessel.

The definition of what constitutes a pressure vessel varies across the globe, depending on what different institutes consider "far enough removed". Typical pressures range from 0.5-1 bar before a vessel is considered a pressure vessel.

Pressure vessels can be constructed from a variety of materials, and in a variety of different shapes. They're usually cylindrical in shape, with end caps called "Heads". This is because more complex geometries are much more difficult to assess for safety, as well as usually more difficult and expensive to manufacture.

Many vessels are made of steel or concrete, due to concretes brittle nature steel cabling is used to reinforce it, so it can withstand the tensile stresses placed upon it. The same method can be employed for other materials which are weak in tension.

Technically any material with good tensile properties could be used, however due to the potential hazards involved standards, codes and regulations are used to govern the manufacture as well as operation of pressure vessels, so as to avoid accidents, and potential loss of life.

Maintenance is especially critical when the production rate, price or pressures involved are high. Because a short shutdown or accident could mean thousands or hundreds of thousands in lost opportunity, it's important to keep equipment in good condition and running within reliable tolerances.

To this end non-destructive testing, can be used, sometimes whilst equipment is in operation to inspect areas, and determine possible defects, and levels of degradation. The important feature of NDT is its ability to gather intelligence on a piece without having to damage it or break into it in anyway. Technologies such as ultrasound, eddy currents and magnetism can be used to inspect from afar, through the limits of physical boundaries.

Typically LFET (Low Frequency Electromagnetic Technique) can be used for the wall plates, and eddy current inspection can be used for welds. Other technologies can be used as well however, depending on client requirements and thoroughness required. Technologies such as magnetic particle, ultrasonic and dye penetrant can also be used.