Welding of pressure equipment and the PED directive

Welding on district heating pipes, pressure vessels and other equipment operating under pressure is not ordinary construction work. If a joint fails here, the consequence is not just a correction — it can be a serious accident. That's why the field is regulated by a common European set of rules that the welder should at least know the framework for, even though formal responsibility typically lies with the manufacturer and the welding coordinator.

The Pressure Equipment Directive, known as PED (2014/68/EU), covers the design, manufacture and conformity assessment of pressure equipment with an allowable pressure above 0.5 bar. The directive's annex sets out a number of essential safety requirements that the equipment must meet, and the manufacturer must be able to document which harmonised standards have been followed — or explain why they have deviated from them.

For the welder pressure-bearing equipment typically means stricter documentation requirements: there must be an approved WPS the welder must be certified for precisely that task and there are often requirements for more extensive control of the finished weld — for example with non-destructive testing such as radiography or ultrasound. None of that is unique to pressure-bearing equipment in itself but the requirements are enforced more strictly because the consequence of an error is greater.

For some pressure-bearing equipment, a nominated (independent) control body must be involved in assessing whether the equipment meets the requirements before it can be CE marked and put into use. It is an extra control instance on top of the company's own quality management and the welding coordinator's supervision and it helps ensure that the assessment is not just an internal process.

The directive also sets requirements for the welding itself. For equipment in categories II, III and IV, the welding procedures and the personnel who weld must be approved by a competent third party (Annex I, point 3.1.2). For equipment in categories III and IV, the same applies to the personnel carrying out non-destructive testing (point 3.1.3).

• 01PED applies to pressure equipment with permitted pressure above 0.5 bar
• 02The manufacturer must document conformity with harmonized standards
• 03Welding procedure (WPS) and welder certification must still be in place — PED is an additional requirement
• 04For some equipment, a nominated control body must be involved before the equipment can be put into use

You don't need to memorize the directive text to weld well on pressure equipment. But it is useful to understand why the requirements for documentation and inspection are stricter here — it's not bureaucracy for bureaucracy's sake, but a direct consequence of the fact that a failing joint under pressure can have serious consequences. Following the procedure to the letter is therefore not a formality, but the core of the work.