What does “In Situ Internal Pipeline Cleaning and Coating” Really Mean?
In situ internal pipeline cleaning and coating is not a new technology or process; however, it’s only recently becoming more widely adopted as a viable and effective industry solution. (Get a background on pipeline coatings in the article An Intro to Pipeline Corrosion and Coatings.) Members of the EnerClear Services team have been specializing in the application process of internal pipe coatings using a two-part epoxy paint via our progressive pigging multiple pass flood coat system since the early 1980s. It’s an incredibly precise process that our team has perfected over the years. This isn’t a process that is often replicated and is not accessible on a wide scale (by way of many companies providing this process).
In a nutshell, it’s a three-step process for existing or new pipelines. This involves a mechanical cleaning stage, a chemical cleaning stage, and the final coating stage. This is all done via our progressive pigging system, where we use specially designed pigs propelled with dried and compressed air. The pipeline is mechanically and chemically cleaned and dried, then coated with a two-part epoxy coating.
The mechanical cleaning stage is where we identify how extensive our program needs to be (is the line new or existing, what is its history, cargo, circumstances, etc.). We run a foam pig to prove line size and determine our next cleaning steps from that point. This can include several soap/water/solvent runs to flush out loose debris, hydrocarbons, wax, and remove the bulk of scale and buildup inside the line. This process is repeated several times as necessary to meet the specified surface preparation requirement.
The chemical cleaning stage is where we clean the pipe to the industry standard (usually NACE 1 or 2 White Metal finish). This entails batching HCl in a "slug" or "pill" of acid between a front pig and a back pig. We then make several inhibited acid shuttles or runs at a controlled rate of travel to loosen and remove all existing mill scale and welding slag from pipe walls. We are monitoring our acid strength (titration) and monitoring fluid samples throughout. This procedure is repeated multiple times with visual inspections done at every access point after every pass to determine pipe wall cleanliness. In addition, we have an extensive quality control program that involves surface passivation to maintain the pipe wall surface as well as an acid etching program to achieve the desired cleanliness and proper profile of the substrate, so that the coating can properly adhere to the substrate. (Related reading: Using Pickling and Passivation Chemical Treatments to Prevent Corrosion.) This is one of, if not the most, integral component of the process. Once we have achieved these targets, we run our “take down” chemicals to complete the drying process prior to coating run.
The third and final coating stage is very similar to the chemical cleaning stage in its execution. This is where we apply the two-part epoxy coating to the line in a multiple pass flood coat system to achieve the manufacturer’s specified nominal dry film thickness (DFT). This is achieved by batching coating between two pigs and ensuring that no air is trapped in the batch. The coating is then run at a controlled rate of travel (via back pressure) multiple times to build up desired coating thickness. The specially designed back pig extrudes the coating as a thin film under pressure (so we know that the coating is filling every pit and covering every square inch). After each pass, inspections and quality control measures are performed to monitor nominal DFT, and then the line is purged utilizing dry air. After multiple coats and once the desired DFT has been achieved, a final cure is performed utilizing hot dry air forced through the line for a specified time. The line is then ready to go back into service.
Benefits of an In Situ Internally Coated Line
Given our ability to coat pipelines in place up to 20–25 kilometers in one pass (dependent on size/scope of project), there are many benefits of an in situ internally coated pipeline. This includes protection of new and existing pipelines from corrosion, erosion, and heat, while resulting in significant gains in throughput and horsepower savings. Additional benefits include a reduction in paraffin buildup, joint protection at welds, less dig-ups appeasing landowners, as well as reduced operating costs in chemical inhibitor and pigging programs. Also, as it is a coating, there are no annulus issues that can be associated with liners and there is no reduction in pipeline ID. In most cases, the epoxy coating is applied to a final DFT of 8–12 mils (or thousandths of an inch) nominally.
Bringing it All Together
It is crucial to note that we have never experienced any coating cracking, blistering, or failures in our company’s history. This is something that we take very seriously and with great pride. Our in situ internal coating process is an "alternative" at the moment, but it is something we are striving to make more mainstream through every project. Our best advertisement is our past work history and track record. Once a prospective client sees our system in action and experiences the benefits of an in situ internally coated line, we often experience extensive repeat work.
There isn’t a "silver-bullet" solution for every integrity issue; as with any solution, process, or technology, there are limitations and proper parameters to define its validity. Given the right conditions and context, we feel that our in situ internal pipeline cleaning and coating system can significantly extend the life of a pipeline and should be considered a valid option for rehabilitation and proactive pipeline integrity protection.