PED vs ASME for Pressure Vessels

Overview

Pressure Equipment Directive (PED – 2014/68/EU)

Mandatory for all pressure vessels in the European Union.
A risk-based approach that categorizes pressure vessels based on their hazard level.
Offers flexibility in material selection and compliance procedures.
CE marking is required for legal acceptance within the EU.

American Society of Mechanical Engineers (ASME BPVC Section VIII)

Primarily used in North America, but is generally accepted internationally.
A prescriptive design approach with strict technical calculations and material requirements, and generally has three classification classes.
Class 1: Standard pressure vessels with a basic design and basic safety factors.
Class 2: More stringent requirements with more extensive technical evaluations.
Class 3: Designed for ultra-high-pressure vessels exceeding 689 bar (10.000 psi).

Implications for the design and engineering of pressurized equipment

Materials Selection

PED permits a wide range of materials, allowing manufacturers to use locally available materials and potentially benefit from short lead times, provided they comply with European standards.

ASME mandates the use of materials approved by the organization, which may limit options and potentially hinder fast delivery.

Production flexibility

PED enables a flexible design process, allowing engineers to incorporate innovations that improve safety and efficiency.

ASME enforces strict guidelines for pressure testing, welding, and stress calculations, which limit design flexibility but ensure uniformity.

Fabrication and Quality Control

Welding and inspection guidelines

The PED welding standards are in accordance with ISO and EN standards. Pressure-retaining components must be manufactured by qualified personnel in accordance with approved procedures for categories II–IV. Key standards include EN ISO 15614-1 (procedure tests), EN ISO 9606-1 (welding qualification), and EN ISO 3834 (quality requirements), which often require approval by a Notified Body (NoBo).

The ASME standards for welding and inspection, which are primarily set forth in the Boiler and Pressure Vessel Code (BPVC), Sections IX and VIII, ensure the safety and integrity of pressure vessels and piping. Key requirements include qualified welding procedure specifications (WPS), certified welding performance qualifications (WPQ), and thorough non-destructive testing (NDT) procedures, such as radiographic or ultrasonic inspections, which are verified by a qualified inspector.

Testing and Certification Process

PED adjusts testing intensity based on risk classification. The certification process involves several key stages, beginning with the design phase and continuing through production to the final assessment. During the design phase, the equipment must be designed in accordance with the harmonized standards (EN 13445 for non-fired pressure vessels, EN 13480 for metal industrial piping, EN 12952 and EN 12953 for boilers)

ASME BPVC testing and certification confirm that manufacturers adhere to strict safety and quality standards through a process that includes, among other things, developing a quality manual and entering into a contract with an Accredited Inspection Agency (AIA), for example for extensive pressure testing.

Remark(s) of the Author...

In summary, it can be stated that the strict material and design requirements of ASME often lead to higher production costs due to the often time-consuming inspections and tests performed by third parties.

The risk-based approach of the PED can reduce production costs because manufacturers can choose alternative materials and test procedures and because faster approvals for low-risk equipment are possible.

This article provides a brief overview of the key differences between PED and ASME standards regarding materials, welding, and testing and inspection procedures. For detailed and comprehensive information, I recommend reviewing both standards before starting a new project.