The EU’s Carbon Border Adjustment Mechanism (CBAM) distinguishes between steel-processing activities that are included in the emissions calculation and those excluded from the defined production boundary. For iron and steel products, reheating, rolling, annealing and galvanising fall within the system boundary, while cutting, welding, plating and finishing are excluded. For steel producers and downstream processors, the boundary determines which production activities and associated emissions must be reflected in reported embedded emissions.
The distinction affects rerollers, galvanisers, wire producers, fabricators, engineering teams and EU buyers. Establishing the correct boundary requires a technical assessment of the production process, including activities performed at other installations or by subcontractors. The assessment is used to determine which stages are treated as part of the defined production process for CBAM reporting.
Covered and excluded processes in the CBAM system boundary
The European Commission’s CBAM methodology lists reheating, remelting, casting, hot and cold rolling, forging, pickling, annealing, coating, galvanising and wire drawing among processes included within the system boundary for iron and steel products. These included stages are incorporated into the embedded-emissions calculation for covered goods.
Plating, cutting, welding and finishing are excluded from the applicable CBAM production boundary. The inclusion or exclusion of specific activities determines which transformations contribute to reported embedded emissions and which must remain outside the CBAM calculation.
Where an in-scope transformation is performed at a secondary installation or outsourced before goods return to a primary installation, the activity is treated as if it had been carried out at the primary installation for the defined production process. This approach is intended to prevent reported CBAM emissions from being reduced by moving a covered stage to a subcontractor while retaining goods within the same production process.
A fabricator undertaking only excluded operations can therefore have a different direct-emissions profile from a reroller or galvaniser. Even when both supply steel products with similar shapes and dimensions, their CBAM calculations must reflect covered activities identified by the methodology rather than treating all downstream operations identically.
Technical boundary assessment using process flow and subcontracting records
Engineering teams are expected to identify the applicable production boundary on the actual process-flow diagram. Furnaces, coating lines, galvanising baths, relevant source streams and shared utilities should be linked to activities included in the calculation.
Outsourced operations require contracts and production records that establish where work took place and how relevant data are incorporated into the emissions calculation. Companies should reassess their boundary whenever a production stage is relocated, subcontracted or otherwise changed.
The technical assessment is expected to be completed before emissions spreadsheets are constructed. A boundary register should identify included and excluded activities, responsible data owners, relevant source streams and outsourced transformations so that an accredited verifier can examine an engineering-based production model rather than relying solely on financial allocations.
For Western Balkan exporters where rolling, coating, galvanising and fabrication may be distributed across affiliated companies or subcontracted sites, legal entity structure alone is not sufficient. The CBAM assessment must follow the technical transformation process, including covered activities performed away from the principal production site.
Supplier contract requirements for MRV under CBAM
Supplier governance forms part of monitoring, reporting and verification (MRV) for steel. Purchase contracts should specify the producing installation, reporting period, emissions-data format, verification requirements and procedures for correcting reported information.
Changes in a supplying plant, production route or precursor can alter the emissions value attributed to a product. If such changes occur without notifying the downstream producer, carbon-cost exposure may arise after the commercial price has already been agreed.
Contractual change-notification requirements support both compliance and commercial risk management by enabling buyers and producers to reassess emissions information when underlying production arrangements change. The same boundary rules also apply to make-or-buy decisions involving included transformations.
Outsourcing an included transformation may remain operationally appropriate but does not provide a basis for excluding that stage from the CBAM calculation. Excluded finishing operations can be assessed separately for broader product-footprint reporting or customer requirements without being incorporated into the current CBAM figure.
Verified emissions data in procurement and compliance files
Steel buyers increasingly need to distinguish between products supported by reliable verified emissions data and those where importers may rely on default values. The distinction has commercial relevance because applicable default-value mark-ups increase during the definitive phase.
Substantiated actual emissions data can reflect characteristics of cleaner feedstock or different production routes. Suppliers able to quantify differences in euros can provide buyers with a clearer basis for evaluating premiums and long-term contracts.
Generic low-carbon claims do not provide evidence at the same level as emissions data linked to a specific installation, production process and reporting period. For producers, the objective is to ensure that commercial emissions figures correspond to legally applicable CBAM calculations.
Compliance files need consistent underlying records that substantiate declared emissions figures. The compliance file should connect purchasing, production, customs and finance documentation with the relevant installation and reporting period.
Routine industrial data, controlled assumptions and documented fallback procedures can help companies accommodate changes in suppliers, production routes, prices or legal requirements without reconstructing calculations from scratch. The same evidence supports customer negotiations, verification reviews and subsequent price adjustments.
Before a transaction or reporting period is finalised, a decision file should link CN code, precursor, production-process boundary, production records and verified emissions value. It should also identify who approves each assumption and document fallback treatment if preferred approaches cannot be substantiated.
A fallback may result in a less favourable commercial outcome but defining it in advance supports assessment of potential exposure before challenges by a verifier, customs authority or authorised CBAM declarant. As CBAM financial implications develop through the decade, unresolved evidence gaps can become recurring carbon costs.
The relevant control remains the production boundary established by the methodology in force, rather than broader voluntary carbon accounting approaches. Correct identification of included transformations and maintenance of traceable evidence help steel companies avoid both omitted emissions and inclusion of activities outside the defined CBAM system boundary.