Structural integrity evaluation for corrosion in spherical pressure vessels

Corrosion is typical of the damage that occurs in ageing pressure vessels and pipelines used in industrial processes as a result of reactive products inside or harsh environmental conditions on the outside. Structural integrity of such components needs to be evaluated periodically to establish the continued suitability of the vessels under operating conditions. The present paper develops a method for Level 2 (as categorized by API 579) fitness-for-service (FFS) evaluation of spherical pressure vessels with localized corrosion. The decay lengths for spherical shells subject to different sizes of corroded areas are calculated based on elastic effects in shells so as to identify the reference volume participating in plastic action. Lower bound “remaining strength factors” of spherical pressure vessels containing corrosion damage are formulated by the application of Mura's variational formulation and the mα-multiplier method. Three alternative design recommendations are given. The effectiveness of the proposed methods is evaluated and demonstrated through illustrative examples and comparison with Level 3 inelastic finite element analyses.