The LR Rules and Regulations for the Classification of Offshore Units require fatigue assessment of the hull interface structures in way of topside facilities. For ship units fitted with a process plant facility or drilling equipment, the support stools and integrated hull support structures of the process plant and other equipment supporting structures, including derricks and flare structures, are considered to be classification items regardless of whether or not the process or drilling plant facility is classed, and their fatigue assessment must comply with the Rules and Regulations for the Classification of Offshore Units.
On the hand, topside structures, typically steel frames that directly support the process facilities, are generally outside the classification scope. Nevertheless, their fatigue performance remains an important part of the design basis. For units with spread mooring arrangement fatigue assessment of both hull structures and topside structures is essential for determining the optimal vessel heading. Classification societies may still get involved in certification services or independent design reviews.
The document provides recommended procedures for fatigue assessment of topside structures installed on floating offshore units in accordance with the accepted practices in the industry. Recommendations contained in this document are not mandatory. These Guidance Notes supplement the mandatory requirements in the LR Rules and Regulations for the Classification of Offshore Units for fatigue assessments of hull structures.