Plastic lining has been applied as a means of providing cost effective corrosion protection to pipelines, and it is widely used for water injection pipelines both onshore and offshore.
Previous Part 1 captured the Benefits of Plastic Lining.
3.0 Plastic Lining
3.1 Geographical Factors
There has been transformation in the way major companies relate to society over the past few years. This is particularly evident in the Oil and Gas Industry, where the historical focus on shareholder value has had to be tempered by a wider consideration of other stakeholders, particularly over such issues as the environment. For example, many companies now report their performance against ‘triple bottom line’ criteria of financial, social and environmental performance. Previously measures of performance were monetary only.
What do these messages mean for the pipeline industry?
- The criteria by which a project is evaluated are no longer purely commercial, but much more complex. Environmental and other social impacts must be included in the evaluation of a project, and the benefits must clearly outweigh these costs for a representative body of stakeholders.
- Projects are becoming increasingly accountable, and directly to the public who grant license to operate. A project must be able to demonstrate that the decision processes taken were responsible throughout.
- The wider public is demanding ever higher standards of performance and that the definition of performance is becoming wider and more inclusive all the time.
One of the direct practical consequences of these factors is the Environmental Impact Assessments as part of project planning. This alone has already had an impact on some projects, causing their re-appraisal and subsequent delay, because the decision processes taken to date were not considered sufficiently robust.
One further practical consequence is that plastic lining should at least be formally considered as a means of corrosion protection.
3.2 Economic Factors
In common with many materials, the cost of plastics varies greatly with the performance demanded of them. The main performance criterion is temperature. For low temperature applications (up to 50° C), the lowest cost plastic HDPE can be used. For higher temperature applications (up to 80° C), the more expensive Polyamides such as “Rilsan” (a nylon 11) can be used. For temperatures up to 120° C, PVDF may be used. This is an expensive material but is already widely used in flexible pipeline manufacture.
Because plastics bring many secondary benefits to a subsea project, it is difficult to generalize cost savings.
Beside the capital cost savings, there are operational savings from not purchasing, transporting and storing toxic chemicals and avoiding plant maintenance. There may also be processing benefits from avoiding inhibitors because they can create foaming in separators, which can seriously disrupt production.
Operational savings can be illustrated over time as in figure 1 below.
Figure 1 – Cash Flows for Three Pipeline Scenarios
Both contractors and operators have explored the potential savings for some time, and their answers have been consistent: cost savings of between 20% and 40% can be achieved for subsea pipeline projects. Other less obvious operational costs include a reduced requirement for inspection and the supervisory effort required by a chemical management system.
3.3 Social Factors
The principal social influences are environmental and health and safety.
Environmental impacts arise from loss of containment incidents, manufacturing processes in the creation and handling of materials and their by-products through life, and finally on their disposal at the end of life.
Loss of Containment
Some would argue that corrosion management by chemical is an unreliable practice. There have been many failures of these systems; often caused by cost savings through either deliberately not using the intended chemical, or supplying inadequate pumping equipment that is unreliable so that a facility operates for some time without protection.
The track record of corrosion prevention by chemical is therefore poor, and leaks occur with remarkable regularity, yet most operators state that leaks are not acceptable.
Sustainable Use of Materials
Pipelines are effectively disposable items. A project seldom considers the end point beyond the design life, even decommissioning options are seldom seriously considered, because discounted cash flow methods result in those impacts being trivialized. The impact of future events are heavily discounted, in direct contravention of the objectives of sustainable development, where the goal is development which meets the needs of the present without compromising the ability of future generations to meet their own needs.
In addition to treating these materials as disposable, stainless steels have higher embodied impacts because they are more energy intensive to make than carbon steel and contain heavy metals (those found in stainless steels include; Cr, Mo, Ni, Va, Mn). Sometimes these metals are extracted from regions that employ dubious labor and environmental practices.
Thermoplastics are also manmade products and therefore also have environmental impacts, but the major advantage of plastics is that they allow toxic corrosion inhibitors to be avoided and this is clearly demonstrated in figure 2.
Figure 2 – Environmental Impacts for Three Pipeline Options Over Time
It is important to recognize that the figure above does not of course represent actual costs. An attempt has been made to internalize the external costs of the environmental impact of various emissions during project lifetimes. The costs used above are (£ per tonne emitted): COx, 7.15; NOx, 1760; SOx, 1540 and the cost of emitting one tonne of OCNS category C chemical is taken as £5,500. These costs have been used on previous pipeline projects, and other costs such as loss of amenity, noise, dust, disposal of any other by-products etc. are not included. Operational impacts are from discharge of 50ppm (gross fluids) OCNS category C chemical only.
To do this exercise properly requires careful analysis, but for the purposes of this analysis, it is obvious that the environmental impacts of a pipeline are dominated by operations when toxic corrosion inhibitors are used.
When corrosion inhibitors are used in raw well fluids, they must be used in volume, and as they are water soluble, they are discharged wherever water is removed from the system. This means that there is a toxic plume from the process water discharge, both offshore and at the shore terminal. Plastic lining therefore offers a means to deliver improved environmental performance by reducing such toxic emissions (always presupposing that a more environmentally attractive treatment can be provided at the treatment facility).
In a climate where offshore operations increasingly have to improve their environmental performance, it is likely that more environmentally responsible means of producing hydrocarbons will be required. If the raw fluid can be transported to the facility using a plastic lined pipeline, other processing options become available for dealing with the toxic substances removed.
For smaller fields with shorter lifetimes as step outs to existing infrastructure, plastic lining offers a way of assuring the condition of the pipeline, making it available for reuse. Maximizing the use of materials by re-using facilities wherever possible is more sustainable, and there are also cost savings, which are briefly discussed in later section.
Health and Safety Costs
There are also health and safety benefits. To do full justice here requires a proper comparative analysis, but simplistically the fact that there are less chemical drums to handle and store reduces personal injury hazards. Having a smaller toxic inventory also obviously reduces the hazard potential.
3.4 Technological Analysis
Plastic lining for subsea pipeline applications would enable a number of novel approaches to developing subsea hydrocarbon fields and these are discussed in the final section of this analysis. However, before these technologies can be enabled, the current difficulty of liner collapse must be resolved, and this is discussed in the following section.
See Part 3 for Plastic Liner Technology.