Finite Element Analysis (FEA) has become an indispensable tool in modern design. It enables detailed evaluation of stresses, deformations, and load responses far beyond what traditional code-based pressure vessel calculations provide. However, a recurring and often misunderstood question persists:
Can a pressure vessel analysis be approved based solely on FEA?
In short: Not under most cases
What FEA Brings to the Table?
FEA is ideal for localized stress evaluations, non-standard geometries (e.g., elliptical nozzles, non-cylindrical shells), weight and cost optimization and detailed analysis of fatigue, buckling, and thermal expansion. But to be accepted as a primary design validation method, FEA must strictly comply with the rules laid out in specific design codes – and most of the time, it doesn’t. This means that the analyst should design the FEA workflow from the beginning to meet specific clauses in ASME VIII-2 or EN 13445, but most manufacturers don’t do that by default. They produce a FEA to show stresses, but fail to structure it according to code methodologies – so the design hardly ever qualifies.
What the Codes & Legislations Say
ASME VIII Division 2 (ASME VIII-2)
The Code allows for full design-by-analysis, including elastic, elastic-plastic, and limit-load methods. Refer to Part 5 for FEA requirements, such as stress classification (primary, secondary, peak), stress linearization, and fatigue screening (para. 5.5–5.7).
EN 13445 (Unfired Pressure Vessels)
Clause 18 permits design by analysis, with strict validation requirements. Annex B describes the use of FEA, including elastic and elastic-plastic analysis routes. Stress evaluation must follow guidance for membrane, bending, and peak stresses. Fatigue analysis must align with Clause 17, and permissible stresses must conform to Clause 5 and material requirements in EN 13445-2.
PED (Pressure Equipment Directive)
The PED (2014/68/EU) does not mandate a particular design code, but requires that vessels demonstrate conformity to the Essential Safety Requirements (Annex I). While manufacturers can use design-by-analysis under PED, the chosen method must be recognized, validated, and verifiable. In practice, Notified Bodies (NoBos) expect designs to follow harmonized standards like EN 13445 or adopt a fully validated design-by-analysis approach comparable to ASME VIII-2.
How Inspection Agencies React
When manufacturers submit only FEA as justification, here’s what typically happens:
Request for Code Calculations
Inspectors ask: Where is your ASME VIII-2 or EN 13445 Part 3 calculation? Even if the FEA looks technically correct, it is not sufficient because it does not produce certainty of the result. Moreover Inspectors themselves are not accustomed to reviewing a FEA report, nor do they have relevant software or hardware to support this review, even if native files were shared.
Concerns Over FEA Validity
Common problems include: No stress categorization (P, Q, Peq, etc.), missing mesh convergence or unrealistic boundary conditions, no reference to allowable stresses or safety factors, no fatigue or plastic collapse check per code. Inspectors often view these as engineering simulations, not code-compliant analyses.
Legal Accountability
Agencies are bound to approve vessels that comply with a code or directive. Accepting an supported FEA – only design exposes them to legal and liability risks. Hence, FEA – only submissions are usually rejected or returned for revision.
Reality in the Field
Manufacturers may see FEA as technically superior and efficient, but regulators enforce code compliance, not engineering opinion.
No math? No approval.
Recommendations for Manufacturers
Always start with code-compliant calculations (ASME VIII-1, EN 13445 Part 3). Use FEA only to support complex geometries, reinforcement validation, fatigue life justification e.t.c.
Final Word
FEA is a powerful engineering tool—but in the pressure equipment world, it is not a free pass. Unless the FEA follows strict code-based methodology and is backed by clear documentation, most inspection agencies will reject it as a standalone justification. Truthfully? “FEA only” is seen as incomplete – no matter how pretty the contour plots. For approval, compliance always comes before cleverness.
