Industrial pressure vessels provide the safe storage of a variety of materials, some relatively harmless and others volatile or hazardous. Regular inspection and testing are a must whether it be for a storage tank or vessel, a boiler, a heat exchange, a process vessel, or some other type of pressure vessel. Because of the extreme pressure in most vessels, it’s essential that they are always in top shape with no leaks, cracks, or deficiencies. 

In this article, we’ll cover the general pressure vessel inspection and testing requirements, as well as what a pressure vessel inspector is looking for during an inspection. 

How Often Should Pressure Vessels Be Inspected?

As a general rule, any pressure vessel should be inspected once it is installed and before it’s put to use. This ensures that any pressure vessel going into service is tested and approved to perform as it should. 

Outside of starting service, pressure vessels should be inspected and tested at least every five years. Specific requirements vary by industry and by hazard potential of the vessel. For example, a vessel containing more hazardous materials will require more frequent inspection than a vessel with relatively safe contents. 

Some common pressure vessel standards include the ASME Boiler and Pressure Code, the AIAA Metallic Pressure Vessel Standard, and the API 510 standard. The specific standard your vessel must adhere to will again depend on your pressure vessel, its contents, your industry, as well as your location. 

5 Types of Pressure Vessel Testing

There are a variety of ways a pressure vessel can be tested, depending on what an inspector is looking for, the contents of the pressure vessel, and what kind of inspection is required. For example, an NDT (non-destructive testing) method is necessary if a pressure vessel is in use. An internal inspection may be required for more in-depth inspections, which must happen while the vessel is empty. Some of the most common types of pressure vessel testing include:

01. Visual Testing

Visual testing is the most common form of pressure vessel inspection. It’s non-destructive and mostly consists of an inspector looking at the vessel’s interior and exterior for any cracks or flaws in the vessel. 

02. Dye Penetrant Testing

This is a unique type of testing where a liquid containing a fluorescent dye is sprayed onto a pressure vessel. When put under a UV light, the dye will glow, identifying any defects or flaws on the pressure vessel’s surface. 

03. Ultrasonic Testing

Ultrasonic testing is used to detect any possible flaws both on the surface of and within a pressure vessel. Using sound waves, an inspector can measure the thickness of a material’s surface, telling them whether there are any interior or exterior defects. 

04. Magnetic Particle Testing

Used to test the surface of a pressure vessel, in magnetic particle testing, a magnetic current is sent through the vessel to identify any deformations or surface defects. 

05. Radiographic Testing

Another volumetric form of testing, radiography is used to detect defects near or on the surface of a pressure vessel. 

Pressure Vessel Inspection Checklist

With a clearer picture of how pressure vessels are tested, you may wonder what a pressure vessel inspector is looking for during that testing. While this is by no means a comprehensive list, here are a few key items inspectors watch out for during both internal and external inspections. 

Internal Pressure Vessel Inspection

Internal inspections are performed when a vessel is empty or not in operation. They require close attention to detail on the inside of the vessel. A few key items an inspector is looking for include:

  • Any possible defects. Anything from a small crack to a bit of corrosion, blistering, or even a more significant deformation can all point to a defective pressure vessel in need of repair.
  • Secure threaded connections. An inspector will inspect all threaded connections to ensure that the right number of threads are engaged to properly secure connection points. 
  • Any openings. If the pressure vessel has any openings, like external fittings or controls, the inspector will check to ensure there are no obstructions to those openings. 
  • Special closures. Any special closures will be inspected to ensure they are closing properly and securely. 
  • High-stress areas. Pressure vessels are designed to store contents at high pressure. Any pressure vessel has high-stress points and areas that are more prone to wear. An internal inspection will closely examine these areas to ensure the pressure vessel is in good shape. 

External Pressure Vessel Inspection

External inspections can be completed when a vessel is in operation or when it is empty. These are usually more frequent than internal inspections as they can be completed at any time. External inspection points usually include:

  • All coverings. Any pressure vessel covering, including any insulation or corrosion-resistant coatings are inspected for defects. Missing coating or insulation can lead to bigger problems down the road, so it’s important to identify and fix them sooner rather than later. 
  • Exterior of the pressure vessel. The entire exterior of the vessel is inspected for any signs of leakage. Whether a vessel contains gas, vapor, or liquid, an inspector will look closely to ensure there are no escape points for any contents.
  • Mountings. All mountings will be inspected to ensure they are allowing for the proper amount of expansion and contraction. 
  • Vessel and vessel connections. All connections will be inspected to ensure there are no cuts, cracks, gouges, or deformations. The inspector should extend this part of the inspection to nozzles, manholes, and reinforcing plates. 
  • Nuts, bolts, and flange faces. Any additional components on the surface of the vessel will be inspected for defects and corrosion. 
  • Shell surfaces and heads. All shell surfaces and heads will be inspected for deformations like blisters or bulges. 
  • Welded joints and adjacent areas. Welded joints are a notorious weak point for any pressure vessel, which is why special attention will be paid to welded joints and surrounding areas. 

Pressure vessel inspection is necessary for the safety of your facility and its employees, as well as for the profitability of your organization. Poorly maintained pressure vessels are both dangerous and expensive. No matter which type of pressure vessel your facility has PALA can ensure it’s always in peak operating condition. 

The experts at PALA are specialists in pressure vessel design, fabrication, and maintenance, so we’re here to support you from start to finish. Holding R, U, U2, and S stamps, we’re qualified to deliver the best in service, time and time again. For more information, give us a call or contact our team.