Enhanced Mechanical Properties of TMCP Clad Line Pipes by EXW


The development of gas fields in harsh environments presents challenges to both designer and producers of clad pipe. The final product is often required to have a demanding combination of properties while remaining economically attractive. Some clad pipes can offer a beneficial combination of strength and excellent toughness of the thermo-mechanically controlled process (TMCP) carbon-manganese steel with the superior corrosion resistance of the internal clad layer. Toughness is a key issue when pipes are transporting compressed gas as fracture propagation is a major concern to high pressure lines. In this case, drop weight tear (DWT) tests are necessary to assess the transition temperature of the pipes while resistance against propagating fracture is verified by means of Charpy impact tests.

Explosion welding is a method with which the clad material is bonded to the carbon-manganese steel utilizing the energy released by explosives. Due to the nature of the process, it is possible to sustain the favorable properties of the TMCP steel, especially the good toughness in terms of both DWT and Charpy impact characteristics. The decoupling of plate rolling and cladding process by explosion welding allows manufacture of clad TMCP line pipe steel plates that exceed the limitations set by roll-bonded clad steels.

This paper presents results of a dedicated study on toughness properties of TMCP pipe material that underwent the explosion welding process for cladding with Alloy 825 and 625. A range of material and wall thicknesses up to around 40 mm has been included to demonstrate the feasibility of this method. Toughness is characterized in terms of both Charpy impact and DWT transition curves to assess the properties before and after explosion welding.

Excellent low temperature toughness as is increasingly required in recent projects was found in the investigated pipe materials.