Underwater Welding

Welding up a metal pipe doesn’t sound terribly tricky but what about when it’s 1 km underwater?  Well engineer Neil Woodward, who’s working with scientists at Cranfield University, is doing just that and he’s also set to set a record in the process!  I suppose Neil that these pipelines are for oil and gas?

Neil -   Yes, that's right.  Oil and gas pipes at varying depths, and there are some at 1km water depth in the North Sea.

Chris -   Are these the major conduit through which we recover the output from platforms out in the North Sea, for example, and then bring it ashore?

Neil -   Yes, that's right.  Transport pipelines that bring it from the oil fields back ashore.

Chris -   And how extensive is that network then?

Neil -   Well there's a massive network of pipes in the North Sea and in the Baltic Sea, all at varying depths and pipelines of various sizes, up to 4 and 5 feet in diameter.

Chris -   So, up until now, if someone had a problem with one of those pipelines, what would they have to do about it?  Is it just a complete decommission job and re-lay a new one?

Neil -   It depends on the depth.  At the moment, if a pipe lies in up to 180 metres of seawater, there are techniques with divers where we can do a repair on a pipeline up to 180 metres seawater.  There's techniques that we can use to repair that pipeline and this also depends on the diameter.  For smaller pipelines, we can use mechanical connectors.  If it’s a large pipeline and it’s beyond 180 metres of seawater then we have an issue with the current methods with divers, and then that's when we have to look at fully remote techniques, which is what I've been working on for the last 9 years.

Chris -   And what is a large pipeline as opposed to a small one?

Neil -   At the moment, we’re kind of cutting off at 30 inches, so between a pipeline diameter beyond 30 inches and up to 48 inches in diameter is where we are looking at welding those pipes subsea.

Chris -   Gosh!  And what would be the sort of pressures and flow rates of the material inside those pipelines?

WeldingNeil -   For pressure tests, it can be up to 200 bar.  The main issue is that they are at depths beyond diver reaches.  We’re looking at being able to repair those pipes with dry hyperbaric welding, which is where we take equipment down and enclose it around the pipe, expel all the seawater inside that chamber and then weld it in the dry.

Chris -   Okay, so this isn't – when we say welding underwater - this is not having some kind of lance that can operate in seawater.  This is actually establishing a complete dry environment around say, a damaged site on the pipe or something.

Neil -   Yes, that's right.  It’s dry hyperbaric welding, which we know we can do in the lab.  In the lab, we’ve used techniques to simulate that pressurised environment and we’ve simulated pressures up to 2 ½ km water depths in the lab.  We’ve done that over the last 10 years, so we know we can do it in the lab, but the main issue is proving that we can do it offshore in a real subsea environment with subsea equipment which has been designed and built.

Chris -   So how does it actually work then?  What do you assemble around the pipe in order to achieve that isolated segment that's the one you want to weld?

Neil -   At the moment, it’s specially-designed equipment.  It’s equipment that's lowered onto the seabed.  It’s effectively almost like a robot, a highly mechanised system which uses a number of electrical and hydraulic systems to be able to close around the pipe and for us to expel all the water inside, make it warm, make it dry - so we dehumidify the environment inside it - fill it with argon, so that we can start welding.

Chris -   And how does your machine know where to weld?  In other words, if you've got a split or a junction in a pipe, how does it identify the two edges and then put a weld across it, and then how does it assess the integrity of that weld?

Neil -   We do have a vision system so we have camera systems that we’ve developed and with regards to integrity, what we’ve been doing is aiming for robustness in the lab so that we know that when we’re welding, we’re monitoring the welding electrically so that we know what a good weld looks like - the trace of a good weld - and we know what a bad weld looks like as we’re welding both visually and electrically.

Chris -   I suppose though that the only way to test it is actually to repressurise the pipe with what was in it before.  So, this is quite an important question because if you get it wrong, then it’s just going to rupture.

Neil -   Yes, that's right.  There have been issues in the past.  At the moment what we’ve done is field trials, so we’ve welded at 280 metres and 350 metres of seawater - for a different application for remote hot tapping application that we should also talk about - and also for a repair application which we welded at 370 metres seawater and 940 metres seawater.  We recovered those welds to the surface and tested those welds.

Chris -   And when you say this hot tapping process, this is where you would have a pipeline that's operating and you want to splice off some of that supply to take it somewhere else?

Neil -   Yes, that's right.  There are applications where it’s beneficial to be able to make a field to flow in a different way.  So, it’s an existing infrastructure, perhaps a large pipeline that's already been laid.  It may have been down there for 20 or 30 years and it’s actually economically beneficial to tap into that pipeline and take out a small branch pipeline to change the flow characteristics in that field.  It’s called ‘hot tapping’ because you're actually tapping into that pipeline while the product is still flowing.  So the field is not shut down whilst you cut into that pipeline.  And we weld inside the connector that goes on to the existing pipeline.

Chris -   If you'd have this technology functional when BP had its problem in the Gulf of Mexico last year, would this have made a difference to the outcome of that situation?

Neil -   That's a massive question.  Potentially, it would’ve given an alternative tool and alternative process for assessing whether something could’ve been repaired...

Chris -   That's Neil Woodward from Isotek Oil and Gas Ltd., and he’s working at Cranfield University.