Orbital welding boosts L and N's reputation

When L and N (Scotland) selected orbital welding equipment it concluded that the Orbimat-C supply and Orbiweld head formed the best possible combination.

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 marketplace.

From simply supplying new products, through to its fully equipped workshop L and N (Scotland) aims to provide its customers with a level of service that is truly second to none.

As a privately owned and independent company L and N (Scotland) can offer customers a wide variety of solutions/options to help them achieve their business goals.

With its in-house team of experienced personnel its customers are given freedom of choice, fully supported by its technical and commercial expertise.

One recent successes L and N (Scotland) has enjoyed is the repeatable welding of small diameter, thick walled instrumentation tubing for the manufacture of subsea wellhead control systems, which are also known as "Christmas tree valves".

These control systems are used to remotely in offshore applications.

The instrumentation tubes used on these control systems is predominantly 9.52mm diameter with a 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 setup 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 (Scotland) has 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 multipositional 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 affects 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 setup this would effect the weld profile produced.

When L and N (Scotland) selected orbital welding equipment it trialled several different types of equipment, but finally concluded that the Orbimatic Orbimat-C orbital welding power supply and Orbiweld enclosed weld head formed the best possible combination for this work.

The Orbimat-C power supply met all of L and N (Scotland) needs and was considered user friendly as well as offering significant advantages over competitive systems.

L and N (Scotland) made their final decision, not only on the functions of Orbimat power supply, but also the build quality and water cooling efficiency of the slimline Orbiweld head which allowed it to accommodate the fittings that it was 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 (Scotland) had an overall package that was considered second to none.

Paul Stobbart of Orbital Welding and Cutting Supplies said: "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 (Scotland) have build 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 (Scotland) is now looking at projects all over the UK.

One client that L and N (Scotland) has assisted, had been using alternative orbital welding systems, but was not able to obtain the consistent and repeatable weld profiles that L and N (Scotland) 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 rework 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 (Scotland) 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 8in diameter with wall thicknesses of up to 32mm.

Back to top