A pressure vessel is a container designed to hold fluids or gases at a pressure significantly different from the ambient environment. These vessels are found across industries and are indispensable, but also potentially hazardous. They store large amounts of energy, and failure can be catastrophic.

A report presented to the World Congress on Engineering in 2010 recorded over 23,000 pressure vessel-related accidents between 1992 and 2001, an average of 2,334 incidents annually. More recently, UK RIDDOR data (2014–2020) reported 387 "dangerous occurrences" linked to pressure systems, highlighting the continued need for robust design, inspection, and compliance.

To mitigate these risks, manufacturers of pressurized systems, such as storage vessels, heat exchangers, piping, boilers, and safety devices, rely on internationally recognized standards to meet essential safety requirements and navigate complex conformity assessments.

Critical for safety: The UK’s pressure vessel code

In the UK, the national standard for unfired pressure vessels is PD 5500, a code first published in 1976 to unify the sector-specific standards that had existed since the 1950s. Now nearing its 50th anniversary (to be marked in 2026), PD 5500 continues to serve as a comprehensive, trusted source of technical guidance across multiple sectors.

The latest version, PD 5500:2024+A2:2025, marks the second amendment to the 2024 edition, which kicked off a new three-year publishing cycle in January 2024:

• Amendment 1 (A1) – Published September 2024.

• Amendment 2 (A2) – Published September 2025.

• Amendment 3 (A3) – Due September 2026.

PD 5500:2024 specifies requirements for the design, manufacture, inspection, and testing of unfired pressure vessels made from carbon, ferritic alloy, and austenitic steels. It also includes material supplements for vessels made from aluminium, copper, nickel, titanium, and duplex steels - supporting both traditional and advanced fabrication processes.

What’s new in amendment 2 (PD 5500:2024+A2:2025)?

Amendment 2 builds on the 2024 edition with technical and editorial updates designed to improve clarity, usability, and alignment with evolving industry practices. Key enhancements include:

Technical and material updates:

• Revisions to BS EN materials in Table 2.1-2.

• New duplex materials for castings and fittings (Tables Du.2.1-2, Du.2.1-3).

• Addition of nickel alloys for forgings, castings, and fittings (Table Ni.2.3-6).

• Updated modulus of elasticity values for nickel alloys (Table Ni.3.6-3).

Design clarifications and drawing improvements:

• Updated nozzle reinforcement procedures.

• Clarification of effective lengths and associated figures and tables.

• Corrections to floating head exchanger drawings (Figures 3.9-1, 3.9-9).

• Clarification and correction of footnotes and stress limits.

New enquiry cases:

• EC 145: Introduces guidance for additive manufacturing using wire-based DED Arc techniques, enabling compliance with UK PE(S)R and supporting UKCA/CE marking.

• EC 147: Provides design rules for nozzle reinforcement in the knuckle region of dished ends, supporting more flexible vessel configurations.

Together, these updates reinforce PD 5500’s role as a forward-looking standard that incorporates both engineering innovation and industry feedback.

A standard with global reach and sector-wide impact

PD 5500 is used not only across the UK but also in Commonwealth countries, the Middle East, and parts of Asia. It is a vital tool for manufacturers and engineers working in:

• oil and gas;

• petrochemicals;

• power generation, including nuclear;

• process plants; and

• food and drink manufacturing.

Its scope makes it a preferred standard among pressure vessel design consultancies, fabricators, and inspection bodies, particularly where UK compliance is required.

Why should you adopt PD 5500:2024+A2:2025?

Adopting PD 5500 ensures that pressure vessel systems are built to meet the highest standards of safety, reliability, and performance. Here's why it's essential:

• Provides a comprehensive reference for design, manufacturing, and compliance.

• Consolidates the latest industry updates, including additive manufacturing and new material specs.

• Offers clarity in interpretation, improving safety and engineering efficiency.

• Helps organizations manage risk, increase market trust, and streamline compliance.

• Supports both domestic regulation and international competitiveness. 

Ensure your organization is complying with the latest pressure vessel safety, as well as future updates to the Pressure Vessel Code, by adding PD 5500:2024+A2:2025 to your collection today.

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