EN 1090-2
Essential Terms
Steel Fabricator
23 Oct 2026
Navigating BS EN 1090-2:2018: Essential Terms Every Steel Fabricator Should Know
By Editorial Team
Table Of Contents
- 1. Introduction
- 2. General Concepts and Project Responsibilities
- 3. Manufacturing, Execution and Execution Classes
- 4. Materials, Components and Preparation
- 5. Erection and Installation Requirements
- 6. Quality Control, Inspection and Non-Destructive Testing
- 7. Understanding Tolerances in Structural Steelwork
- 8. Common Mistakes to Avoid
- 9. Quick Reference: Key Terms in BS EN 1090-2:2018
- 10. Frequently Asked Questions
- 11. Conclusion
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Structural steel fabrication requires precision, consistency, and effective quality control at every stage of production. From selecting the correct materials to cutting, welding, assembling, inspecting, and erecting steel components, every activity must meet the applicable technical requirements to ensure the safety and reliability of the finished structure. BS EN 1090-2:2018 specifies technical requirements for the execution of steel structures. It provides a framework for manufacturers, fabricators, contractors, and quality professionals to understand and implement the requirements associated with structural steelwork.
However, understanding the standard involves more than following fabrication procedures. It also requires a clear understanding of its terminology. Terms such as execution class, execution specification, essential tolerance, functional tolerance, and supplementary non-destructive testing (NDT) have specific meanings that influence how steelwork is manufactured, inspected, and accepted.
Misinterpreting these terms can result in incorrect fabrication decisions, dimensional discrepancies, inspection failures, unnecessary rework, and delays during installation.
This article explains the key terminology associated with Clause 3 of BS EN 1090-2:2018 and explores how these concepts apply to everyday structural steel fabrication and construction activities.
General Concepts and Project Responsibilities
Understanding the basic terminology used in BS EN 1090-2 helps establish clear responsibilities between designers, fabricators, contractors, inspectors, and other parties involved in a construction project.
Construction Works
Construction works refer to the overall construction project, including buildings and civil engineering structures. These may incorporate structural steelwork alongside other structural and non-structural elements.
For example, an industrial building may include steel columns, roof trusses, floor beams, cladding, foundations, and supporting systems.
Works
Within the terminology of the standard, works refers specifically to the structural steelwork covered by the relevant execution requirements. Understanding this distinction helps identify which parts of a wider construction project fall within the scope of the steelwork execution activities.
Structural Steelwork
Structural steelwork consists of steel structures and fabricated steel components designed to perform structural functions. Examples include steel frames, columns, beams, trusses, platforms, and supporting structures.
The quality of these components depends on material conformity, dimensional accuracy, suitable fabrication procedures, and appropriate inspection.
Constructor
The constructor is the person or organization responsible for executing the works, as understood within the applicable project and contractual arrangements.
Responsibilities may involve coordinating fabrication activities, managing execution requirements, maintaining documentation, and ensuring that the work complies with the relevant specifications.
Structure
A structure is an arrangement of connected components designed to carry loads and provide the required stability and rigidity.
For instance, a steel-framed industrial building relies on the coordinated performance of columns, beams, bracing, and connections to resist the loads acting on the structure.
Manufacturing, Execution and Execution Classes
Manufacturing and execution are closely related, but they are not identical. Understanding the difference helps organizations establish appropriate production controls and inspection procedures.
Manufacturing
Manufacturing includes the activities required to produce a steel component or assembly. Depending on the product and project, these activities may include:
• Procurement and verification of constituent products.
• Material identification and traceability.
• Cutting, drilling, shaping, and preparation.
• Assembly, welding, and mechanical fastening.
• Surface preparation and protective treatment.
• Dimensional inspection and verification.
• Preparation of quality records and delivery documentation.
Each activity must be controlled according to the applicable execution specification and the requirements relevant to the component.
Execution
Execution covers the activities involved in completing the structural steelwork. This includes manufacturing, erection, inspection, and the associated documentation required by the applicable requirements.
For example, producing a steel beam in a workshop is only one part of execution. Its transportation, installation, connection to other structural elements, and the required verification activities may also form part of the execution process.
Execution Specification
An execution specification is the collection of technical information and requirements established for the particular steelwork. It supplements or qualifies the general requirements of the execution standard for the project concerned. It may identify applicable execution classes, materials, fabrication requirements, tolerances, inspection activities, and other project-specific conditions.
A clear execution specification helps prevent misunderstandings between the designer, fabricator, contractor, and inspection personnel.
Execution Class (EXC)
An execution class defines a set of execution requirements applicable to the structural steelwork or relevant components and details. BS EN 1090-2 uses execution classes EXC1, EXC2, EXC3, and EXC4. These classes represent different levels and combinations of execution requirements. The applicable class must be established for the relevant works through the appropriate design and project specification process.
Fabricators should not assume that the same execution class applies automatically to every steel structure. The specified class influences the execution controls and verification activities that may be required.
For example, a project with more demanding structural or consequence-related requirements may require a higher execution class, depending on the design basis and applicable provisions.
Practical takeaway: Confirm the specified execution class and project requirements before starting fabrication. This helps establish the correct procedures, personnel qualifications, inspection arrangements, and documentation.
Materials, Components and Preparation
Material conformity and traceability are essential to reliable structural steel fabrication. The terminology used in BS EN 1090-2 helps distinguish the materials entering production from the components manufactured from them.
Constituent Product
A constituent product is a material or product incorporated into the structural steelwork. Examples include structural steel sections, plates, stainless steel products, bolts, welding consumables, and other relevant products.
The required properties and documentation depend on the product type and applicable specifications.
For example, when a steel plate is used to manufacture a load-bearing bracket, the fabricator must establish that the plate meets the specified material requirements and maintain the necessary identification and traceability.
Component
A component is an individual part of a steel structure. It may be a single fabricated item or an assembly of smaller parts.
Examples include a steel column, a welded beam assembly, a truss section, or a prefabricated support frame.
Cold-Formed Component
Cold-formed components are produced by forming steel products, commonly flat steel products, into specified profiles without relying on hot forming as the principal forming process.Examples include cold-formed channels, angles, and profiled steel sections used in building systems and secondary structural applications.
The applicable material and execution requirements must be considered when incorporating these products into structural steelwork.
Preparation
Preparation refers to activities carried out on constituent products before they are assembled into components.
These activities may include material identification, storage, cutting, shaping, drilling, hole preparation, and other operations required to achieve the specified dimensions and condition.
Incorrect preparation can affect assembly accuracy, connection fit-up, weld quality, and the overall dimensional conformity of the finished component.
For example, inaccurately positioned bolt holes may prevent a steel connection from being assembled correctly on site, potentially requiring corrective work.
Erection and Installation Requirements
Fabrication quality alone does not guarantee that a structure will be installed correctly. Erection planning and suitable documentation are important for controlling risks during construction.
Design Basis Method of Erection
The design basis method of erection refers to the erection approach on which the structural design is based.
The intended erection sequence and temporary structural conditions may influence stability during installation. Therefore, the erection method must be consistent with the relevant design assumptions and project requirements.
Erection Method Statement
An erection method statement describes the planned procedures for installing structural steelwork on site.
Depending on the project, it may cover:
• The proposed sequence of erection.
• Crane operations and lifting arrangements.
• Temporary bracing and stability measures.
• Connections and alignment procedures.
• Site safety controls and responsibilities.
• Inspection and verification activities.
A properly prepared method statement helps coordinate site activities and reduces the risk of installation errors or instability during erection.
For example, a steel frame may require temporary bracing until sufficient permanent connections have been completed. The erection sequence must account for these temporary conditions.
Quality Control, Inspection and Non-Destructive Testing
Quality control helps establish whether materials, fabrication activities, and completed components meet the specified requirements.
Inspection and Test Plan (ITP)
An Inspection and Test Plan identifies the inspections, tests, verification activities, and records required at relevant stages of execution.
An ITP may include material verification, dimensional checks, welding inspections, bolt installation checks, surface treatment inspections, and final acceptance activities.
The required inspections depend on the project specification and applicable execution requirements.
An effective ITP also clarifies inspection responsibilities and identifies relevant hold points or witness points where specified.
Nonconformity
A nonconformity occurs when a specified requirement has not been fulfilled.
Examples include:
• A component manufactured outside the specified dimensional tolerance.
• Incorrect material supplied for a particular application.
• A weld that does not satisfy the applicable acceptance criteria.
• Missing or incomplete quality documentation required for acceptance.
Nonconformities should be documented, assessed, and addressed through the established quality management process. Corrective actions must be appropriate to the nature of the issue and the applicable technical requirements.
Supplementary Non-Destructive Testing (NDT)
Non-destructive testing involves examining materials or components without rendering them unusable. Supplementary NDT refers to testing required in addition to the relevant visual examination or other specified inspection activities.
Depending on the material, weld configuration, defect type, and project requirements, methods may include:
Magnetic Particle Testing (MT): Used to identify relevant surface and near-surface discontinuities in suitable ferromagnetic materials.
Penetrant Testing (PT): Used to reveal surface-breaking discontinuities in suitable non-porous materials.
Eddy Current Testing (ET): Uses electromagnetic induction to detect certain surface or near-surface discontinuities in conductive materials.
Ultrasonic Testing (UT): Is a method that uses high-frequency sound waves to detect and assess internal discontinuities.
Radiographic Testing (RT): Uses X-rays or gamma rays to produce an image that can reveal certain internal discontinuities.
Not every weld requires every NDT method. The applicable method, extent of testing, personnel competence, and acceptance criteria must be determined in accordance with the relevant specification and standard requirements.
Practical takeaway: Inspection activities should be planned before production begins. Selecting testing methods only after a defect is discovered may result in avoidable delays and additional costs.
Understanding Tolerances in Structural Steelwork
Dimensional accuracy is important because structural steel components must fit together correctly and perform according to the design requirements.
Tolerance terminology helps establish the permissible limits for dimensions and geometry.
Tolerance
For a specified dimension, tolerance is the difference between its upper permissible limit and its lower permissible limit.
Tolerances define the permitted variation from the specified dimension or geometrical condition.
Essential Tolerance
Essential tolerances are geometrical tolerances associated with the structural requirements necessary to satisfy the design assumptions for mechanical resistance and stability.
These tolerances help ensure that the fabricated structure conforms to the geometrical conditions assumed during design.
Functional Tolerance
Functional tolerances are geometrical tolerances associated with functional requirements beyond mechanical resistance and stability.
They may relate to fit-up, alignment, interfaces with other components, or other specified functional requirements.
For example, the position of a steel bracket may need to satisfy a particular functional tolerance so that connected equipment can be installed correctly.
Special Tolerance
Special tolerances are tolerances that specify requirements that go beyond the standard tabulated tolerances for a particular project.
Such requirements need to be clearly specified so that the fabricator and inspector understand the required limits and the method of verification.
Manufacturing Tolerance
Manufacturing tolerance refers to the permissible variation in dimensions resulting from the production of a component.
Maintaining dimensional control during cutting, drilling, welding, and assembly helps prevent cumulative dimensional errors.
Essential vs. Functional Tolerances: Why the Difference Matters
Essential and functional tolerances serve different purposes. Essential tolerances relate to the geometrical requirements associated with structural resistance and stability, while functional tolerances address additional functional needs.
A component may satisfy one set of tolerances without automatically satisfying the other. Both must be considered wherever applicable.
For this reason, fabricators should review the specified tolerances before production and verify the finished component against the relevant requirements.
Common Mistakes to Avoid
Understanding terminology is most useful when it informs everyday decisions. The following mistakes can undermine execution quality:
Confusing essential and functional tolerances: Meeting one tolerance category does not necessarily demonstrate compliance with all applicable geometrical requirements.
Overlooking the execution specification: General knowledge of the standard does not replace the need to review the requirements established for the specific project.
Assuming every weld needs the same NDT: Inspection and testing must reflect the applicable requirements rather than a one-size-fits-all approach.
Neglecting traceability and records: Incomplete material records, inspection results, or nonconformity documentation can complicate verification and acceptance.
Planning quality checks too late: Inspection requirements should be integrated into production planning to reduce delays, repeated work, and avoidable costs.
Quick Reference: Key Terms in BS EN 1090-2:2018
| Term | Main purpose |
|---|---|
| Execution specification | Defines the technical requirements applicable to the particular works |
| Execution class (EXC) | Establishes the applicable set of execution requirements |
| Constituent product | Identifies materials and products incorporated into the steelwork |
| Component | Describes an individual part or assembly within the structure |
| Preparation | Covers activities required to prepare products for assembly |
| Inspection and Test Plan | Organizes required inspections, tests, and verification records |
| Nonconformity | Identifies failure to fulfil a specified requirement |
| Supplementary NDT | Provides additional examination where required |
| Essential tolerance | Addresses geometrical requirements associated with structural resistance and stability |
| Functional tolerance | Addresses additional geometrical and functional requirements |
| Special tolerance | Covers specific project requirements beyond standard tabulated values |
Frequently Asked Questions
What is BS EN 1090-2:2018?
BS EN 1090-2:2018 specifies technical requirements for the execution of steel structures. It addresses relevant execution activities, including fabrication, erection, inspection, and associated technical requirements.
What are the execution classes in BS EN 1090-2?
The standard uses four execution classes: EXC1, EXC2, EXC3, and EXC4. They represent different sets of execution requirements. The applicable class must be established through the relevant design and project specification process.
What is the difference between essential and functional tolerances?
Essential tolerances relate to geometrical requirements associated with structural mechanical resistance and stability. Functional tolerances address additional functional requirements, such as fit-up or alignment.
Is supplementary NDT required for every structural weld?
No. The applicable NDT method and extent depend on the relevant execution requirements, project specification, weld characteristics, and acceptance criteria.
Conclusion
Understanding the terminology in BS EN 1090-2:2018 is essential for maintaining consistent execution practices, effective quality control, and reliable structural steelwork. Terms such as execution class, constituent product, nonconformity, supplementary NDT, and functional tolerance each contribute to a shared understanding of the requirements that apply throughout fabrication and erection. For manufacturers and fabricators, the practical value of this knowledge lies in applying the correct requirements at the right stage. Reviewing the execution specification, maintaining material traceability, planning inspections, controlling dimensions, and documenting nonconformities all contribute to reducing avoidable errors and improving production consistency.
A clear understanding of these concepts also strengthens communication between designers, fabricators, contractors, and inspection personnel. When terminology is interpreted consistently and applied in accordance with the relevant requirements, steel construction projects are better positioned to achieve their specified quality and performance objectives.
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