An ideal weld

As the oil and gas sector moves to deeper waters and the tolerance of welds get ever tighter, alleviating problems during installation and operation is more important than ever. Justin Cunningham looks at the technology responding to industry demand.

It's an age old problem: fit a square peg in a round hole. And this is certainly a dilemma when you are building an oil and gas pipeline to transport fossil fuel back to shore. The problem is that while pipes are manufactured to one set of standards, tighter tolerances are required when it comes to actually fitting the pipes together. The result is that pipes coming straight from the manufacturer have tolerances of around 2mm, yet when it comes to fitting them together, the tolerance needs to be less than 0.5mm.

"We look at the shape of the pipe ends," said Denise Smiles, chief executive of Optical Metrology Services (OMS). "We found that people sometimes find they are trying to weld a slightly oval pipe end with a slightly square pipe end. It really depends on the manufacturing process.

"If the tolerance is in excess of 2mm for fit up, then chances are no matter what shape or spec the pipes are, they will go together. But generally in most of the projects we see now, the fit up is between 1.5mm and less than 0.5mm."

You don't need precision measurement to know the outcome runs the risk of being a poor join between the two – something the industry has been progressively, and actively, looking to improve upon. There has been a drive for tighter tolerances, particularly as many move to deeper waters, as the joins come under more stress and strain.

"But in addition tolerances are getting tighter because oil companies want the licence for pipelines to last 10 or 15 years," Smiles explained. "And governments won't approve that unless they are absolutely sure they have achieved the very best they can in putting it under the water."

For example, when it's on ecologically sensitive areas like the recent Gorgon project in Australia that's going over some coral escarpments, governments simply can't allow any kind of environmental damage. So the result is that tolerances for the project become incredibly tight. It was this fundamental demand that saw OMS develop measurement equipment to bring new resolution to the calliper measurements used by old school engineers for generations.

"What the calliper does is take a load of diameters," explained Smiles. "But, it doesn't really give you the shape of the pipe end and it doesn't tell you where the centre is."

Changing this is the SmartFit tool from OMS, which is able to take 2,000 measurements of a pipe end diameter in about 10s. And furthermore, once it has taken those measurements, the system runs an analysis that gives a probability that, "if pipes are chosen at random with no rotation of the pipe end, this is the number of problems you are going to have," said Smiles. "But, if you put these pipes together in random selection and rotate the end to the very best fit, i.e. 'SmartFit it up', your fit up issues will drop from maybe 5% down to 0.5%.

"Then the very best fit up would be if the pipes are so different in shape that you've really got to match them end-to-end, otherwise you are never going to get the pipes together. But, to be far, that is very rare."

For the offshore industry, it means that they only take pipes out to sea that go together. And when day rates for boats can be as high as £750,000 a day, delays, downtime, and excess cargo are a costly venture.

For the welders, which can be both manual and automated processes, the software of Smartfit will be able to immediately show what rotation is needed for the best fit, and allow them to proceed with confidence.

"We draw a big arrow on the pipe, so when it goes to the welders they just turn the pipe to match the arrow on the previous pone," said Smiles. "It avoids having two hours downtime as they try to fit pipes together that simple won't work."

The company continues to push the boundaries when it comes to offer inspection tools, with the development of an internal inspection system that uses a combination of a camera and laser sensor. These are able to go inside welded pipes and look in very fine resolution for defects. This has become particularly important for Inconel clad pipes as they do not permit any flaws in the welds at all.

While this kind of inspection can be done in a number of ways, perhaps the most significant is using a crawler robot. The tool being developed by OMS will be able to go down 1km down into the pipe, something nobody in the world can do.

"The laser and a camera system move up and down the welds and take a lot of cross weld images," said Smiles. "While the camera gives a visual view of the inside of the pipes, it is the laser that really quantifies it and ensures it is well within the parameters."

Technology transfer

While the offshore industry, and pipeline fitting, has been the primary target for OMS, it has found that actually other sectors could benefit from its measurement technology. The tools are not limited to measuring diameters nor stopped by corners, as has been the case in the past.

An example has been the use of sensing technology under the M25. The motorway uses massive storage containers to store water during heavy rain and stop flooding across the roadway. There were concerns initially that due to the weight of the road above, they would squash containers and reduce their capacity.

"So our lasers went in and measured the volume of the containers to make sure that they were sufficient," said Smiles. "We've also done work on Crossrail where the water industry wanted us to have a look at their existing water pipe. What they wanted to do was put a pipe inside the old Victorian pipes that are under the ground without having to dig up Ludgate Circus. And we were able to offer them this kind of internal inspection."

The need to inspect welds and other internal surfaces is a trend that is set to continue. Historically, engineering tolerances only go one way, as technology allows greater precision in manufacture and assembly. And this seems to be no different.