New solutions for old pipeline problems…

Pipeline integrity is an increasing challenge to the energy industry as the infrastructure is aging, and new field developments are introduced in both deep and remote areas of the world. Older assets were sometimes constructed without considering the need for future inspection pigging, utilizing Intelligent Pigs. This is of course a cost driving issue, since modification work needs to be considered for making the pipelines possible to inspect today or sometime in the future.

The Challenges

The current development of the offshore market shows an increased focus upon subsea field development. Production flow lines, and other in field pipelines are hard to inspect, due to the potential lack of launcher/receiver facilities on the subsea templates, or the costs of vessel time involved in rearranging the pipe work.

Other examples of unpiggable pipelines in the Oil/Gas industry is typically refinery pipe work, off loading lines and transport pipelines. For the upstream market, issues around inspection of casings, risers, j-tubes and single ended flow lines, are frequently discussed.

Today more focus has been put into investigating the integrity of the unpiggable pipelines. This is mainly due to more stringent codes and regulations, and of course increased focus on the environment. Lack of technology and budget is no longer a good excuse to avoid demonstrating your pipelines integrity in most areas of the world, since the costs of a potential leak has a more dramatic cost impact than an inspection campaign.

The next question that appears is what kind of technology is available in the market to suit the regulatory requirements and the operators own standards for unpiggable pipelines? The answer is highly dependant upon pipe length and location, since a refinery pipe section will not require the same solution as a subsea flow line. External ultrasonic solutions as guided wave, corrosion mapping, TOFD and CHIME will always be an option, together with pulsed eddy current and other standard NDT methods. The fact that the pipeline can be inspected in operation is attractive to most pipeline operators. The methods described are mostly selective, except from Guided Wave ultrasonic, which is more a screening method, and needs more verification work from one of the selective methods.

The gathered inspection data from the selected areas can be used together with other information about the pipeline such as operational conditions and environmental information, and be used as base data for the performance of direct assessment.

There are also a number of tethered systems for internal interventions available in the market. These are mostly ultrasonic tools, and the difference between systems is most evident when comparing resolution, range and the propulsion mechanism. These tools can be propelled as a free swimming pig, but the umbilical which contains communication cables and power, often prevents the line to be inspected during operation. Nevertheless, the cost effectiveness of tethered inspection is comparable to most other solutions especially when considering price pr. metre, and the fact that by inspecting the pipeline from the inside it is not needed to remove coating, soil, rock dump and other obstructions.

AGR Pipetech has been in this industry since –94, and has experienced how the request for in line services has increased dramatically. Operating from Norway, the North Sea has been a good starting point, forcing AGR to develop hardware designed for high resolution and harsh environment from the start. The fact that the recent offshore development projects, and future field developments aims deeper and warmer, requires the industry to introduce new tool architecture packed to handle the increased pressure but based on the same basic ultrasonic principles.

The biggest challenge for this industry is however to introduce a propulsion unit which is able to negotiate various pipeline installations over an acceptable length at an acceptable speed. Most tractors are designed for larger diameters 30”+, and the smaller tractor versions does not have the desired pull force. Some pneumatic crawlers and electro hydraulic versions are available, but the lack of a convincing track record, suggests that using this technology is combined with a good portion of risk. The reason for this is probably the rich variety of pipelines within this industry, making it difficult to design a standard tool, thereby never leaving the prototype stage.

The Solution

During the mid nineties AGR spent a lot of focus into the development of a propulsion unit designed specifically for unpiggable pipelines. The most effective way to accomplish this, was to develop a tool which was able to create its own differential pressure in a liquid filled pipe.

In a closed or barred pipe line without flow, the solution for the self propelled pig was to install the driving pumps inside the pig hull and thereby create the necessary flow through the pig itself in stead of through the pipe line. Under normal operational conditions a pressure differential on 0,5 BAR or less, is enough to move the Pipe Intruder system. When resistance is met, the pressure, and consequently the driving force, will build up to overcome the resistance.

The self propelled pig may be driven in both directions by turning the suction and discharge flow from the internal pig pumps in the desired direction.

Today, the PipeIntruder is the locomotive of the fleet of tools and is available in ranges from 8” – 30”. Above 30” electro hydraulic tractors are available, specifically designed for off loading lines.
All combinations of tools are available together with a variety of umbilical winches ranging from 1 km up to 10 km.

The capabilities of the PipeIntruder have demonstrated to be very useful in combination with the WeldScan system, which incorporates TOFD ultrasonic capabilities. The tool stops on selected positions in the pipe, and perform a sweep over the pipe circumference looking for cracks or LOF defects in the welds. This is possible because of the combination between on line observation of the tool movement, and the possibility to position the tool with a +/- 1 mm axial accuracy in the pipe.

The fact that this technology has been used for over 10 years, in both the upstream and downstream market, in various single/multi phase liquids and depths, clearly suggests that the technology is robust and introduce new possibilities for pipeline interventions.