An extensive experimental programme has been carried out to characterise the mechanical parameters and the fracture response of two steels, BS1501 and A533B. These are widely used in pressure vessel technology. The role of load history on improvements in cleavage fracture toughness has been investigated. Finite element analyses have been performed to simulate and verify the findings of the experimental programme. Scatter within experimental cleavage toughness data has been described by using the model proposed by Wallin [1] and combined with Chell [2] model for WPS effect. A stress matching approach to predicting the fracture response of the as received, as well as the warm pre-stressed specimens is also suggested. Using the stress distributions from the finite element analyses prediction of fracture after WPS is examined and results are compared to both the experimental data and those obtained by the combined Chell -Wallin [3] model of failure probability. The significance of residual stress field in enhancing of cleavage fracture toughness following warm pre-stressing has been highlighted.

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