Thermoplastics: Reducing Pipeline Rehabilitation Risk

This article was featured in the “Industry Comment” section of the June 2022 edition of Trenchless Works Magazine published by The Westrade Group

Pipeline rehabilitation is a complex technical process that requires specialised knowledge, skills and experience. When considering a pipeline rehabilitation project, it is critical to consider all the factors that can influence the cost, the timescales, and the longevity of the repair. When these considerations are factored in correctly, the low-cost solutions almost inevitably end up costing significantly more over the lifetime of the pipeline.

The relentless pursuit of cost reduction and budget cuts has led to the emergence of a myriad solutions being offered – some of which can put projects at risk during installation and frequently lead to very short lifetimes. This repeatedly tarnishes the reputation of all rehabilitation technologies, hindering progress. The cheapest solution is often not the most reliable.

A reliable and robust solution

The safest and most reliable method of rehabilitating a pipeline is frequently the installation of high and medium-density polyethylene liners. Liners ranging from loose-fitting fully structural slip liners to tight-fitting semi-structural Die Draw liners (historically Swagelining or Die Drawing) and everything in between can be installed. These proven PE 100 and PE 80 materials deliver reliable, fully qualified, and extensively tested materials that already dominate low-pressure water and gas pipelines throughout the UK and Europe.

When correctly engineered these solutions offer a highly controllable installation process that only uses the natural properties of the materials themselves without any need for difficult to control post curing, spraying or post-pressurisation to establish the finished product. Polyethylene liners, when implemented correctly, offer a robust, reliable, environmentally friendly, and cost-effective method of rehabilitating pipelines with greater than 100 years design & life expectancy.

Die Draw towhead attached to a pe100 liner

How do you reduce risk and maximise return?

So how do you maximise the return, lower the risk and provide the fastest resolution for your pipeline rehabilitation project? The answer is surprisingly straightforward: Use the correct materials with the right people with the right expertise & experience. NEVER deviate from the project specification, equipment, material, processes, or tolerances.

At first glance, this answer may appear over simplistic and nothing more than common sense, however the reality is that failure to follow this simple guideline has repeatedly caused significant problems across the industry.

When a complex project experiences a failure, the engineering solution required to rectify the problem is often more challenging than the original problem.

The best way to ensure a project is completed within the fastest time and for the lowest cost possible is to ensure it is implemented and completed correctly in the first place.

Why experience matters

We have examined many instances of pipeline rehabilitation project failure over the last 30 years. In some cases, we have been brought in to engineer an appropriate solution after a project has already failed within a few years or less of installation. What we have seen, with alarming regularity, is that in almost every case, the root cause of the project failure has been non-adherence to the project specifications. If the process is difficult to control in the first place it invariably leads to problems.

We have seen difficult to control processes – often using thermoset rather than thermoplastic materials – go on to cause catastrophic project failures requiring complex, lengthy and expensive resolutions. A key advantage of polyethylene is that it is a thermoplastic produced in a controlled factory environment rather than a thermoset which is usually cured on-site with all the additional variables that environment entails. As a polymer engineer, I view thermosets as yesterdays’ materials and thermoplastics as the future. Thermoplastics can be recycled whereas thermosets cannot.

My intention is simply to highlight that when complex engineering solutions are completed by qualified individuals with the right experience, there is a much higher probability the project will be carried out successfully. This is true of whatever type of liner material is selected.

If a project fails because a defined process has not been followed, it is not the fault of the process or the technology. It is a failure of an industry that is willing to permit deviations or accept judgement calls from people who are not qualified to make the alterations to the process.

The Variables

Modern trenchless technology requires fully designed, engineered and checked solutions for the installation phase, it’s no longer acceptable to just turn up with the equipment and attempt to pull a liner in. Unfortunately, this practice is still occurring and in the event of a failure, the resolution will cost several times the original project budget.

When a lining solution is correctly engineered, all variables will have been meticulously examined, understood and where necessary, mitigated against. The calculations and planning take months of work by qualified engineers. The system is considered as a whole and when unknowns are introduced, they can have cumulative, knock-on effects that increase the chance of failure.
The Considerations
There are many different thermoplastic lining techniques available. The success of the project will be largely dependent on the ability of that specific technique to meet the client requirements.

There are 2 broad classifications of thermoplastic lining solutions,

  1. loose fit
  2. tight fit.

A loose fit solution, often referred to as slip-lining, is more common across the industry and is widely recognised as the simplest form of thermoplastic PE lining system due to the ease of installation.

Slip-lining is an excellent solution as long as it meets the clients’ requirements. More often than not, however, slip lining will be proposed because it is relatively easy as opposed to correct.

Slip-lining remains a good solution where flow capacity is not critical for a pipeline owner. This is often the case over shorter distances but for longer projects, consideration must be given to the reduction of flow capacity over the entire length of the pipeline.

Die Draw Large Diamtermeter pe100 liner inside host pipe

In the circumstances described above, where flow capacity is a critical consideration, a tight-fit lining solution will offer a superior engineering solution. The initial cost may be a little higher and the installation a little more complex but this is mitigated against by utilising qualified engineers with appropriate experience. The whole life cost of the project will likely be significantly lower as the solution will be more likely to meet the client requirements, while using less material.

It is also worth noting that the Die Draw technique can be used for loose fit options too, with a fully structural full pressure bearing liner able to deliver greater flow capacity than a slip liner.

A holistic design approach with experienced, qualified engineers that considers all variables & requirements of the entire project will inevitably deliver a superior solution, provide quantifiable savings, maximise flow rate, meet all engineering tolerances and maximise the pipe life. Specialist winching design requirements and associated temporary works is critical for all these solutions whether slip lining or die drawing. The pipeline rehabilitation consultancy must have sufficient knowledge of these requirements and be able to propose a suitable solution.

In Summary

If you want to ensure the success of your pipeline rehabilitation project, make sure you look at the total, lifetime cost of the proposed engineering solution. Take everything into account. Use qualified individuals with relevant experience who understand the situation, the environment, the calculations. Explore historical projects in detail and ensure there is a clear understanding of what needs to be achieved. Ensure all influencing factors are identified and integrated into the solution – especially the ones that are less obvious. Relevant experience is critical to the success of your project.

Above all, choose an industry-proven technique with a long history of successful installations. The installation of high and medium density polyethylene liners by qualified engineers will go a long way to guaranteeing the success of the project.