King of the slopes

When it comes to laying pipes in inaccessible areas, most pipeline contractors are confronted with the challenge of how to lay the pipes in the steep terrain. For this purpose, cable crane systems can provide an efficient solution. Pipes, construction material, and equipment can be easily transported over all kinds of territory and positioned precisely at any point along the track. This method has been used successfully for several years.

The first cable crane system ever used in connection with a major pipeline construction was a simple build ‘tower and cable construction’ which was installed and operated for the Trans-Alaska Pipeline project in 1977. One of the last sections of the project was a 45° steep slope at Thompson Pass with a length of approximately 850 m. With the help of the cable crane system it was possible to lay the 48 in. and 24 m long pipes.

The methodology has essentially been the same since 1977, but it has been significantly improved and refined in terms of safety, efficiency, quality, and with respect to the environmental impact.

Work method

A cable crane system consists of a strong wire rope which is tensioned, in mountainous terrain, from a point in the valley to a point at the mountain top, with several towers and special ropeway components. Furthermore, the system is equipped with a crane unit that is mounted on the track rope. Loads can be lowered and lifted with the crane unit’s two independently controllable winding devices. The crane unit itself is pulled up and down along the track rope with a haul rope which is wound on a winch. The winch is located at the top station.

For the construction of a pipeline in steep terrain by means of a cable crane system, the following workflow can be realised in an easy and safe manner:

• Installation of the pipeline exactly along the pipeline centre line.
• Transportation of a spider excavator into the steep slope for trenching.
• Transportation of the pipes and construction equipment to the intended location.
• Precise positioning of the pipe into the inclined trench.
• Holding the pipes steadily during the welding operations.
• Transportation of padding material and filling of the trench.
• Reinstatement of the right-of-way (ROW) where the pipeline has been constructed.

Construction challenges and how to handle them

Various challenges can arise during the planning and construction of a pipeline that need to be solved. Generally, these challenges are particularly demanding in sections that are difficult to access – such as mountainous areas, steep slopes, and inaccessible terrain – with a conventional means of transport. The following key challenges have to be considered when it comes to the laying of pipes.

The terrain

The terrain and landscape may impact the length of the pipeline and the way the pipes are laid. Areas with large differences in altitude, mountains or swampy terrain can make it difficult to find a pipeline route. Some contractors may choose to make an expensive detour or build many kilometres of access roads to avoid certain inconveniences.

The cost-efficient alternative method to overcome these challenging terrains is the use of a cable crane system. With such a system the pipes, construction material, and machinery can be transported in mid-air to the intended location. The ropeway runs directly above the ROW and can load and unload goods at any point along the track. An advantage of a cable crane system is that it is flexible and can be installed at a range of unanticipated locations and in sections of up to 3000 m. Furthermore, pipes can be positioned easily and safely in slopes with an inclination of up to 70°.

By using a cable crane system, pipelines can follow direct routes and contractors do not have to lay several additional kilometres of pipeline to avoid tough terrain. Consequently, savings can be made on costs and resources.

Transportation of pipes

Efficient material planning and a working supply chain are crucial for every pipeline construction project. When a construction site is in an area with limited access for excavators, drilling equipment and sidebooms, the logistics department faces a considerable challenge. The solution is a cable crane system that can easily and safely transport large pipes and construction material to exactly where they are needed. Additionally, the system can be used to move all kinds of machinery, e.g. excavators, to any place along the track where civil works or trenching works shall be performed. Loads of up to 20 t and more can be lifted and unloaded along the ropeway route.

Laying and welding of pipes

Not only the transport, but also the laying of pipes in a steep and critical slope can be solved with a cable crane system. For proper erection of a pipeline, an exact working procedure during positioning, welding, and other installation steps is important. In areas with a high inclination, working with traditional methods such as sidebooms, large welding equipment, and sandblasting is largely impossible. The cable crane system makes pipelaying at the exact intended position and welding in steep and hazardous terrain uncomplicated. Since each crane unit of a cable crane system has two independently controllable winding devices, the pipes can be perfectly lifted and lowered into the terrain to fit in the trench. For the following welding works, the cable crane holds the pipe steadily in place. The pipe is fixed with a welding clamp, just as it would be done in flat terrain, ready to start the welding process.

In relation with the sandblasting and coating, a special platform can be attached to the cable crane system and be transported above the welded section. The tasks are then performed from this platform, which is hanging above the pipe.

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