Cost estimation model of structural steel for superstructure of wellhead platform in oil and gas industry

Abstract

Cost estimation during early stages of construction should be accurate and quick as possible. For accurate and quick cost estimates for steel structure material of offshore structure such as Wellhead Platform with minimum input of data, this study proposed an approximate cost estimation model that is based on standard quantities of structural steel for superstructure/topside. These standard quantities were calculated from the mean value of percentage for respective steel section to the overall structural steel weight and the mean value of percentage for respective steel strength to the weight of each steel section. Forty four (44) bid projects from bidding data of Wellhead Platform by Engineering, Procurement, Construction, and Commissioning (EPCC) contractor were collected and analysed for model development and five (5) projects for model verification. Seven (7) steel sections consist of plate, welded tubular, seamless tubular, beam, miscellaneous steel, grating and stair tread with respective strength of High Strength, Through Thickness Properties (TTP) and Mild Strength steel were identified that accounted for overall structural steel costs. The completed cost estimation model were validated through inter-rater agreement between Subject Matter Expert (SME) in the field and verified by comparing the estimated cost calculated by the model and the actual bidding cost. The result showed that the model yield an error range less than +8%. It is expected that the model presented in this study will support the existing estimation practice while increasing the level of confidence in engineered costs for fixed offshore structures.