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Oil, Gas, Petrochemical Industry News
News Release from: Orbimatic | Subject: Orbimat-C
Edited by the Processingtalk Editorial
Team on 14 November 2005
Oil and gas welding success in Scotland
L and N (Scotland), a well established valve and welding provider to oil and gas customers, has specialised in welding small diameter, thick walled tubing on 'Christmas Tree' valves
Formed in March 1996, L and N (Scotland) is now well established as one of the leading valve and specialised welding solution providers in the Oil and Gas market place From simply supplying new products, through to their fully equipped workshop, L and N aim to provide their customers with a level of service that is truly second to none
This article was originally published on Processingtalk on 13 Jan 2003 at 8.00am (UK)
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With an in-house team of experienced personnel, customers are given freedom of choice, fully supported by technical and commercial expertise.
One recent successes L and N have enjoyed is the repeatable welding of small diameter, thick walled instrumentation tubing for the manufacture of sub-sea wellhead control systems, which are also known as 'Christmas Tree Valves'.
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These control systems are used to remotely in offshore applications.
The instrumentation tubes used on these control systems is predominantly 0.375'' (9.52mm) diameter with a 0.10'' (2.77mm) wall thickness, these tubes are fabricated and then welded using automatic orbital TIG welding equipment.
In the past it has been considered that the orbital welding process has to be used in combination with complicated internal purging methods, which involves balancing the internal pressure of the backing gas to help control the condition of the weld pool.
This set-up makes use of a pressure gauge, often referred to as a magnahelic gauge and is commonly referred to as the 'balanced pressure' system.
However with the balanced pressure system results are not always found to be fully repeatable, especially in long or complex pipe runs which can make it difficult to obtain a consistent and balanced pressure.
L and N have approached this whole subject in a more logical manner and used the latest advancements in orbital welding equipment to overcome these problems and obtain some very successful and reliable results.
Orbital welding by nature is a multi-positional process and engages a variety of welding conditions during each pass performed.
These different conditions are caused by the result of gravitational force on the welding pool.
The gravitational effect gives at least four different conditions during each revolution.
This goes some way to explain why the 'balanced pressure' system is not always repeatable in these applications.
The 'balanced pressure' system may prove to be more successful if the internal pressure where to be adjusted according to the position of the weld pool.
With this in mind the welding parameters should then be established according to the position of the weld pool.
In the 'up-hill' and 'down-hill' positions the weld pool is suspended by the material directly below the weld pool.
And in the 'over-the-top' and 'underneath' position the welding pools in not suspended in any way.
If this same logic is applied to the adjustment of welding parameters then it is quite easy to get suitable results without the need for controlling the internal gas pressure.
An important consideration when developing procedures using this method, is the way in which the welding system itself changes parameters between each level.
The effect of gravity on the weld pool will not be instant, but will take effect gradually as the tungsten electrode travels around the circumference of the tube.
This means that the change in welding parameters should not change instantly, but should slope down gradually between different levels of welding current.
Several other factors also contribute to the successful welding of these small diameter thick wall tubes.
Some of these factors are often overlooked as minor issues and are not considered as important issues.
Probably the most important issue is the selection of material and control of specifications.
It is essential that the supply of material is controlled closely to keep a consistent material composition throughout any project.
The largest influence is the sulphur content of the material which can cause serious welding issues if this is not controlled closely.
Sulphur effects the way in which heat moves through the material and will control the weld profile.
Another issue is the preparation of the tube prior to welding.
The tube should be prepared with an appropriate preparation machine which will leave the tube end perfectly square and burr free.
If there is any inconsistency in set-up this would effect the weld profile produced.
When L and N selected orbital welding equipment they trialled several different types of equipment, but finally concluded that the Orbimatic Orbimat-C orbital welding power supply and Orbiweld enclosed weld head to be the best possible combination for this work.
The Orbimat-C power supply met all of the L and N needs and was considered user friendly as well as offering significant advantages over competitive systems.
L and N made their final decision, not only on the functions of Orbimat power supply, but also the build quality and water cooling efficiency of the slim line Orbiweld head which allowed them to accommodate the fittings that they were going to use in its standard form.
When the orbital welding equipment was combined by the after sales backup and support service offered by Orbital Welding and Cutting Supplies, L and N had an overall package that was considered second to none.
Paul Stobbart of Orbital Welding and Cutting Supplies quoted 'We offer not just technology leading orbital welding equipment, but also a support package which helps our customers obtain optimum results to the benefit of us all'.
Since the introduction of this equipment L and N have built a reputation throughout Aberdeen as the market leaders in the welding of these small diameter, thick walled tubes.
This reputation has now spread further a field and L and N are now looking at projects all over the UK.
One client that L and N have assisted, have been using alternative orbital welding systems, but were not able to obtain the consistent and repeatable weld profiles that L and N could produce.
This customer has seen their high percentage of weld defects reduced to nearly zero and have in turn seen a large increase in production output.
When the re-work time is added to the equation it can be consider that the production rates there have dramatically increased.
This technique is not limited to the offshore industry and can be used for a whole host of other applications and industries and L and N do not only specialise in the orbital welding of thick walled tubes.
They have recently achieved excellent results using the orbital welding process for 3mm OD tubes with a 1mm wall thickness and have just embarked on a project using orbital welding equipment for super-duplex pipes from 3'' to 8'' diameter with wall thicknesses of up to 32mm.
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