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Orbital Welding and Subsea Applications

Orbital welding is a computer based welding process which is typically used to generate high quality, repeatable welds.  Welding specifications are completely programmed into the machine before welding begins, and once it does, there is minimal interference required by the operator, reducing the risk of human error.

As orbital welding is a computer controlled process, welds generated via an orbital welding procedure are both repeatable and consistent.  This is due to the operator’s ability to program specific parameters into the machine, including an alarm or ‘cease welding procedure’ should these parameters not be met.  Welding programs can be set in such a way that very strict tolerances are automatically monitored and adhered to, which allows the operator to meet essential welding variables with ease.  This process is particularly effective when working with thin wall and small diameter tubing, from which subsea hydraulic lines are predominantly fabricated.

There are two different types of orbital welding machines: autogenous, which does not use filler wire, and non-autogenous, which does.  When using an autogenous machine the operator gains the ability to better control the internal weld bead profile as there is no wire being used.  This eliminates the risk of internal bore reduction as required in hydraulic & control line tubing systems.  The risk of external weld contamination is also reduced due to the closed head welding environment.  For this reason, the majority of orbital welding performed by Diverse Welding Services is done so using an autogenous welding process.

Diverse Welding Services have both types of machines available, with qualified personnel & procedures for use of both systems on super duplex, duplex, inconel 625 and 316 stainless steel.  These materials are widely used for subsea applications as they combine high corrosion resistance and high mechanical strength with excellent resistance to seawater and marine environments.  For these reasons they are particularly well-suited for applications exposed to high stress in aggressive chloride-rich environments.

When fabricating or repairing subsea piping systems, orbital welding is preferred over manual welding as the welds produced are of an extremely high quality and have an exceptionally low failure rate when tested via 100% radiographic testing regimes.  Corrosion resistance rates are also maximised in the ‘as welded’ condition, proven by DWS, when samples tested under the G48 Method A – Pitting Resistance Test resulted in weight loss to be less than 0.36g/m2 for stainless steel. 

Orbital welding has many advantages.  The machine controls heat input, and so material quality and integrity is easily maintained.  The machine also features a recording data log which enables the user to track weld processes and guarantee consistency.  Due to the enclosed structure of the weld head, gas is kept inside the head and as such is effective when welding in confined spaces and challenging environmental conditions.  This feature decreases the amount of gas required and is therefore more economical than standard manual welding.  Inspection procedures are also simplified as the orbital welding machine prints a docket listing the parameters which have been adhered to whilst welding has taken place, meaning the operator does not have to be supervised to ensure the welding performed meets the welding procedures and standards required.  Welds are also generated in a faster weld time when compared to manual tig welding.

As the development of new energy reserves increases, so does the need for subsea infrastructure.  The ability to supply high quality, internationally competitive subsea fabrication is crucial to the ongoing growth & success of the Australian oil and gas industry.  There are currently a large number of unprecedented technical challenges involved with subsea oil and gas development and orbital welding is playing an increasingly vital role.