A Review on Fracture Properties of Welded High Strength Steel (HSS) for Low Temperature Application

Abstract

The technological evolution in structural steels are pointing towards high strength steel, especially in the offshore and marine applications. Therefore, there is need to have knowledge on the fracture behaviour of high-grade steel welded joints to improve and contribute to the potential upgrades of the design criteria. Lightweight structures (with reduced cost and weight) that guarantee high-quality/highstrength weld-able joints has become the trend in recent research. Natural gas and oil reservoir which have the potential to boost economic growth and play a vital role in the future energy requirements lie beneath the waters of the world’s ocean. This water depths ranges from a few hundred to several thousand metres. Explorations and production activities in these offshore waters have revealed depths of 2000 metres and more. Generally, water depths of 1000m (known as mesopelagic zone) and above have low temperatures of about -2oC. At this temperature, seawater freezes and ductile materials are susceptible to brittle fracture. This has significant effects on installation of oil and gas pipelines at low temperature. This have become challenges, which calls for enhanced engineering techniques to cope with the risks of fatal failures. Due to inherent metallurgical phenomenon, mechanical properties heterogeneity, residual stresses and geometrical defects, cracks propagates easily especially at the welded joints. Studies have been conducted on the fracture properties of the HSS materials. This paper is aimed at reviewing the effects of chemical composition on the microstructural properties of HSS materials in low temperature applications. The concept of fracture mechanics as applied to fracture behaviour of welded joints with focus on the effects of low temperature on HSS materials is presented. The fracture toughness in deep water applications, where temperature at the depth of water is in semblance to the arctic region environment is briefly discussed. In conclusion, API X100 TMCP materials have been recommended as a types of high strength steels (HSS) for structural steel material applicable for low temperature because of the properties, chemical compositions and development methods or manufacturing processes. Also, modern welding techniques often used in the arctic region is suggested to be applied for the deep offshore materials for sustainability, effectiveness and fitness for service requirements.