Spare Parts and Materials Standardisation in Pressure Vessel Maintenance: A Critical Review of the Evidence for Inventory Cost Reduction

Pressure vessels are among the most capital-intensive and safety-critical assets in process, energy and marine industries, and the materials and components consumed in maintaining them account for a substantial and persistent share of operating expenditure. Standardisation of spare parts and construction materials is widely promoted as a route to lower inventory cost, yet the supporting evidence is distributed across separate research communities that rarely address one another. This critical narrative review examines whether, and under what conditions, standardisation reduces the cost of holding and replenishing pressure vessel maintenance materials without eroding integrity assurance. Literature was identified through structured searching of open scholarly indexes, supplemented by backward and forward citation tracking and by consultation of authoritative institutional documents, with a defined search period closing on 3 July 2026. Sources were appraised for design adequacy, transparency, external validity and the alignment between reported findings and the claims they are used to support. The synthesis develops five layers of standardisation, spanning design, materials, components, data and process, and traces the causal pathways by which each is proposed to influence inventory cost. The evidence is strongest for data standardisation and for multi-criteria classification linked to stocking policy, where independent case studies report inventory value reductions of roughly fifteen to seventy per cent alongside maintained or improved availability. Evidence for materials standardisation in pressure-retaining service is markedly weaker, and is constrained by divergent allowable-stress bases between major construction codes, by damage mechanisms that are specific to alloy and environment, and by the absence of studies that quantify inventory consequences of material rationalisation decisions. Claims that additive manufacturing dissolves physical inventory are only partially supported; the most rigorous process-industry assessment identifies economic viability for approximately one per cent of stock keeping units. Principal unresolved questions concern the safety cost of substitution, the transferability of commonality models to code-governed components, and the near-total absence of longitudinal cost evidence from pressure vessel populations. Standardisation is best understood as a conditional lever whose returns depend on data quality, criticality structure and regulatory constraint rather than as a general economy.