Pressure Vessel Testing

Pressure vessels store liquids and gases under pressure for use in industrial and domestic settings. In domestic settings, examples include hot water storage tanks, compressed air cylinders as used in diving, and oxygen cylinders. Industrial applications are more interesting in terms of inspection, and include natural gas storage, chemical storage and various applications in the process, petrochemical and oil industries.

Operation of these vessels carries an inherent danger, and design, manufacture and operation is often backed by strict regulations and law. For this reason, often the exact definition of a pressure vessel varies from country to country, with a typical definition including any vessel with a maximum operating pressure of above 15 psi.

Pressure vessels are typically constructed of steel, though any material with a good tensile strength, and chemical stability for the chosen application could be used. Standards and design codes such as those proposed by ASME provide a list of suitable materials and guidelines for use at various temperatures, and these are generally used.

Welding on pressure vessels is also an issue, as the design of cylindrical or spherical pressure vessels using forged or rolled parts, generally requires welding, and this can introduce weakness. The heat of welding can weaken the material, and introduce cracking and other defects into the vessel. To detect these defects we use non-destructive testing techniques.

Inspection of pressure vessels ensures they're operating safely, and helps avoids accidents, downtime and loss of profits. For these reasons alone, regular inspection is a good idea. And generally inspection is carried out at regular intervals in order to pre-empt problems and build up a reliable pattern of data. In the event something should go wrong, these records can show that maximum action was taken prevent problems, and protect staff.

NDT or Non Destructive Testing is used for inspection, due to its non-invasive nature. Technologies such as ultrasonic testing and electromagnetic testing are the main technologies used, however dye penetrant and magnetic particle can also be used for a more thorough inspection.

The American Petroleum Institute also provides standards for the non-destructive inspection of pressure vessels, and requires an API qualified technician with the right certification to perform the inspection. This can be more thorough, though provides more coverage, and is an option depending on the thoroughness the client requires.

Techniques such as LFET (Low Frequency Electromagnetic Technique) are used for the inspection of the wall plates, and techniques such as BFET (Balanced Field Electromagnetic Technique)are used for the inspection of welds.