Prediction of Liner Wrinkling During High Strain Bending of Mechanically Lined Pipe

Abstract

A high demand for transport of corrosive fluids subsea has generated interest in solid corrosion resistant alloy (CRA) and bi-metal pipes. Bi-metal pipes, including hot-roll bonded (HRB) clad and mechanically lined pipes (MLP), are made of a carbon steel (CS) pipe lined with a CRA layer. Mechanically lined pipes, where the CRA liner is held inside the host pipe by means of an interference fit, offer shorter lead times and are considerably more economical than equivalent solid CRA and HRB clad pipes with a metallurgical bond between CS and CRA layers. Reel-lay is a cost-effective method for installing subsea pipelines up to 18” (457.2 mm) in diameter. However, plastic straining associated with reeling may trigger wrinkling of the CRA liner. Two approaches for safe installation of reeled MLPs have therefore been proposed: pressurised and non-pressurised reeling. This paper focuses on reel-lay installation at atmospheric pressure. Nevertheless, the numerical analysis framework presented is also applicable to MLPs installed at elevated pressure in a scenario where they are subjected to bending after being depressurised. Small-scale mechanical tests were carried out to assess the effect of manufacturing and cyclic plastic bending on the tensile behaviour of the CRA liner. After full-scale bending trials had been undertaken, they were simulated numerically to demonstrate the suitability of the proposed numerical approach for predicting liner separation from the host pipe and subsequent wrinkling during high strain bending. To improve ovality prediction, which governs liner separation and wrinkling, the authors developed an advanced metal plasticity model.

Inspection of Liner Wall Thinning and Interface Debonding in Bimetallic Lined Pipes Using Pulsed Eddy Current Testing

“…The massive pipelines used in oil and gas (O&G) production and transportation are exposed to some of the most aggressive industrial environments. As is often the case in the subsea and offshore O&G industry, the inside is exposed to the corrosive ingredients of hydrocarbons, while the outside is required to withstand mechanical loads and impacts [1,2]. In order to simultaneously solve the corrosion problem and provide the required strength to maintain structural integrity, the use of a solid corrosion-resistant alloy (CRA) and bimetallic composite pipes is in high demand [3][4][5][6].…”

“…Generally, BLP pipes provide excellent corrosion protection. However, due to manufacturing-related anomalies, wrong handling during storage, transportation and installation, and unsuitable selection of CRA material for the actual operational conditions, corrosion damage and geometric deformations can occur at the outer layer, internal layer and also the interface [1,2,9,10]. Among these failures, liner wall thinning and interface debonding, which are invisible and inaccessible from outside, are difficult to identify and, thus, pose great risk to the operational safety of BLP lines.…”