HFI-Welded Pipes: Where Are the Limits?

The high frequency induction (HFI) method for production of longitudinally welded pipes was introduced in the early sixties. Initially HFI-welded pipes served more or less only as a low-cost product for standard applications without increased requirements. The growing demand for energy in North America, Europe and the Far East over the last decades has resulted in an increase in the exploration and exploitation of natural gas and oil resources in remote environments under aggravated conditions. This led to more demanding requirements on the mechanical-technological properties of the pipes. Additionally, an accelerated increase of safety awareness can be observed for operation of pipelines, in order to prevent environmental or population damage. Salzgitter Mannesmann Line Pipe GmbH (MLP) coped with the growing responsibilities by having optimized the HFI-welding process over the last decades, in order to produce top quality pipes suitable for practically all requirements. The modifications to this manufacturing process have resulted in a smaller scatter in geometrical pipe parameters and in optimisation of the relevant mechanical-technological properties. This led to HFI-welded pipes which, besides the aspect of lower cost, now offer several further advantages, compared to seamless pipes or SAW-pipes, and enables the use for economical and safe applications. The present paper deals with the compliance of the progressive application requirements, using HFI-welded pipes from Salzgitter Mannesmann Line Pipe works. It will be focussed on the increased production capabilities and mechanical-technological properties of diameters up to 24^″ (610.0 mm) and 1^″ (25.4 mm) wall thickness, as well as higher API 5L and 5CT grades up to X70M for sour-service and weldable P110, respectively. As there is also an increasing tendency to use steel pipes for structural applications which require an enhanced spectrum of dimensions in recent years, the paper will provide details of the upgraded product portfolio for structural hollow sections (circular, square and rectangular) at MLP.