Welds on pipes and plates must comply with specific UNI standards. UNI EN ISO 9692 regulates joint preparation and beveling, UNI EN ISO 3834 defines quality requirements for the welding process, and UNI EN 1090 sets the criteria for metal structures with CE marking. Cold mechanical edge preparation using beveling machines and pipe-facing machines ensures precision and eliminates thermal alteration of the material.
Joint preparation: The foundation of standard-compliant welding
The quality of a weld on pipes and plates begins long before the electric arc. Edge preparation is the preliminary phase that determines regulatory compliance and the mechanical strength of the final joint.
Beveling—i.e., chamfering the metal edges—creates the necessary space for optimal penetration of the weld pool. Without proper preparation, the filler material cannot fully fuse with the base metal, compromising the joint’s structural integrity.
For thicknesses above 3–4 mm, preparation is typically required to ensure full penetration. Below this threshold, edges may simply be aligned after thorough cleaning. Above 4 mm, however, standards require specific geometries that vary depending on thickness and the type of stress expected.
GBC plate beveling machines allow precise preparation on thicknesses from 6 to 120 mm, with variable angles up to 90° and constant millimetric tolerances, ensuring compliance with regulatory requirements from the very first phase.
UNI EN ISO 9692: The standard for joint preparation
The UNI EN ISO 9692 series is the technical reference for bevel geometries. It consists of four parts, each covering specific processes and materials.
Part 1 (2013 edition) defines edge preparations for manual arc welding with coated electrodes, MIG/MAG, TIG, and gas welding of steels. Part 2 covers submerged arc welding, while Part 3 (2016) focuses on technical specifications for MIG and TIG welding. Part 4 (2005) is dedicated to clad steels.
Each part specifies root gaps, bevel angles, land heights, and allowable tolerances. The maximum permissible misalignment is 1.5 mm for all joint types, regardless of thickness.
Bevel types according to the standard
The standard prescribes different geometries depending on the material thickness.
V bevel with a 60° angle is often required for thicknesses between 5 and 20 mm, with a root gap of 2.5–3.5 mm. This is the most common preparation for single-sided butt joints.
X bevel is used for thicknesses above 15 mm when welding from both sides is possible. It reduces the amount of filler material required and limits deformation, with root gaps of 3–4 mm.
U and J bevels, also known as compound bevels, are frequently used for thicknesses above 20 mm. They cannot be perfectly achieved with thermal cutting and require mechanical machining. They further reduce the weld volume compared to V- or X-bevels.
GBC pipe beveling machines, with an operating range from 0.40″ (10.3 mm) to 40″ (1016 mm), allow all these types of preparation with constant precision on steel, carbon steel, stainless steel, copper, duplex, and inconel.
Preparation methods: Thermal vs. Cold mechanical
There are two main approaches for preparing edges: thermal processing and cold mechanical processing.
Thermal cutting (plasma or oxy-cutting) offers speed and can remove large amounts of material quickly, though with variable and generally lower precision. Plasma is used for medium thicknesses, while oxy-cutting with a double torch is suitable for very thick materials. The main limitation is the heat-affected zone (HAZ), which alters the metal’s microstructure and often requires subsequent cold mechanical finishing to restore the edge to the required welding standards.
Cold mechanical processing is preferred when superior precision and surface quality are needed. It ensures millimetric tolerances without any thermal alteration of the base material—an essential factor for sensitive materials like duplex, super duplex, and inconel, where surface structural changes can compromise mechanical and corrosion-resistance properties.
The operational flexibility of cold-machining equipment allows variable thicknesses and different angles with the same machine. GBC cold cutting and beveling machines for pipes, with capacities from 1″ to 100″, offer this versatility while maintaining consistently high quality standards.
UNI EN ISO 3834: Quality requirements and preparation
UNI EN ISO 3834, updated in 2021, defines the quality requirements for fusion welding of metallic materials. It covers the entire process—from preparation to final inspections.
The welding coordinator oversees edge preparation, ensuring that geometries and tolerances comply with project specifications. The process documentation (WPS – Welding Procedure Specification) must indicate the preparation method used.
The standard is divided into three operational levels: Part 2 defines comprehensive quality requirements, Part 3 normal requirements, and Part 4 basic requirements. Each level includes different controls on the preparation phase, with stricter checks for higher levels.
UNI EN 1090: Execution classes and relationship with UNI EN ISO 3834
UNI EN 1090 defines the requirements for manufacturing and CE marking of steel and aluminum structural components, introducing four execution classes (EXC1, EXC2, EXC3, EXC4), each associated with increasing requirements for inspections, skills, traceability, and welding quality.
Execution classes do not directly define edge-preparation methods but determine the expected quality level and the controls applicable to the welding process, including joint preparation.
Although certification practice often correlates EXC classes with UNI EN ISO 3834 levels, this is not a strict requirement but rather a commonly adopted association for certification purposes:
- EXC1 → ISO 3834-4 (basic requirements)
- EXC2 → ISO 3834-3 (normal requirements)
- EXC3 and EXC4 → ISO 3834-2 (comprehensive requirements)
This correspondence facilitates conformity assessment according to EN 1090 structural criticality levels. However, the standard does not impose a fixed pairing: the type of structure, design loads, materials used, and project specifications ultimately determine the appropriate ISO 3834 level.
For EXC3 and EXC4—characterized by stricter requirements (e.g., for structures subject to fatigue or extreme conditions)—requirements for joint preparation checks also increase. Bevel geometry compliance becomes an integral part of inspections, in coordination with ISO 5817 (quality levels for weld imperfections) and qualified procedures (WPS/WPQR).
Preparation in critical sectors
Some industrial sectors impose even stricter requirements on joint preparation.
Oil & gas and pipelines: absolute tightness is critical. Bevels on thick sections and special materials must be machined with millimetric precision. Extreme environments, such as offshore or subsea, allow no margin for error.
Petrochemical industry: frequently uses duplex and super duplex, where thermal alteration can trigger localized corrosion. Cold preparation is therefore mandatory—not optional.
Naval and offshore sectors: certifications require complete traceability of preparation processes. Each bevel must be documented and inspected before welding.
Heat exchangers: require perfectly tight joints with varying thicknesses. Preparation must ensure constant geometries even on small-diameter pipes, where precision is even more critical.
GBC solutions for these industries cover the full range of needs, from small maintenance tasks to large structural operations.
Overview of complementary standards
Alongside the main standards, other regulations complete the framework:
UNI EN ISO 5817 defines acceptance levels for imperfections in welded joints. UNI EN ISO 15614 regulates procedure qualification via WPS and WPQR documentation. UNI EN ISO 9606-1 sets criteria for welder qualification across different preparation types.
Advantages of professional mechanical preparation
Investing in professional cold-preparation equipment delivers measurable benefits. Quality consistency eliminates operator-dependent variability, ensuring repeatable results.
Reduced rework and scrap have a direct impact on costs. A properly prepared edge the first time avoids production downtime for corrections.
Automatic compliance with standard requirements reduces risks during certification inspections. With professional GBC machines, preparation parameters always fall within the ranges specified by the standards.
Return on investment is therefore measured in execution speed, consistent quality, and reduced waste. For mass production or critical sectors, professional mechanical preparation is not an option—it is a necessity to remain competitive and compliant.
Discover the full range of GBC equipment for pipe and plate processing, designed to ensure full compliance with current standards for cutting and beveling quality. Contact us for a personalized consultation.