Pressure equipment — rules, categories and periodic inspection
Why a pressure vessel is not just a tank, and what the law requires before and after it is put into use
Many process plants contain equipment working under pressure — boilers autoclaves pressure vessels and pipe systems. If it goes wrong here the consequence can be serious: a steam leak sudden pressure release or in the worst case an explosion. Therefore pressure equipment is subject to special legislation that both the manufacturer and the person using the equipment must know.
§Pressure Equipment Directive (PED)
The rules are based on the EU's pressure equipment directive, 2014/68/EU, often called PED (Pressure Equipment Directive). The directive applies to equipment with a maximum permitted pressure above 0.5 bar and sets requirements for how it is designed, manufactured and CE marked before it can even be sold or used.
§Danish legislation: design and use
In Denmark meat production got a big boost when farmers joined cooperative slaughterhouses. This meant larger quantities more uniform quality and strong exports especially of bacon. With industrialization much of the work moved from the individual butcher to larger production facilities where tasks were divided into specialties.
§Risk categories
The equipment is divided into risk categories—from category I to category IV—based on a combination of maximum pressure (PS) volume (V) and nominal size (DN). The higher the category the greater the potential consequence if something fails and the stricter the requirements for control and documentation including often involving an independent authorized body.
| Category | Typical level | What it means in practice |
|---|---|---|
| I | Lowest risk | Simpler assessment and documentation requirements |
| II–III | Mid-level | Increasing demands for inspection during manufacturing |
| IV | Highest risk | Tightened requirements, often involving an independent inspection body |
§Periodic inspection
Pressure equipment wears over time — corrosion, material fatigue and weakened welds are all risks that may not be visible from outside. Therefore the equipment must be periodically inspected by an accredited inspection body which checks, among other things, wall thickness, welds, safety valves and signs of corrosion before the equipment is allowed to continue in operation.
§The role of the safety valve
A safety valve is the last barrier against overpressure: it opens automatically and releases pressure if it rises above the safe level and closes again when pressure is normalized. A blocked maladjusted or disabled safety valve removes this barrier — this is therefore one of the issues taken most seriously in both daily rounds and periodic inspections.
“A pressure-bearing system is safe because someone has followed the rules for it—not because it looks calm from the outside.”