By D. E. Russell, PICA Corp.
Pipelines are routinely replaced well before their design life has been expended. The CAPEX for a new pipeline often runs into the millions of dollars, and yet at least half of this CAPEX can be deferred for many years if non-destructive inspection (NDT) techniques are used to identify areas thinned by corrosion. These can be surgically repaired at a fraction of the replacement cost, and the pipeline can remain in service for many years.
Pipelines in oil, gas, water, wastewater and slurry service, running at pressures over 100 PSIG, are usually made of steel, cast-iron or ductile-iron, i.e. metals that corrode. If the inside and outside of the metal pipes are not protected from corrosion by good-quality liners and coatings, it is likely that local areas of corrosion will result in premature failure of the pipes.
Many cities in North America, and in fact, the whole industrial world, live with water and sewer leakage rates of 30 per cent or more. Unmetered drinking water that leaks out of poorly coated pipes is a source of lost revenue for the water companies and a source of pollution for our waterways. Because drinking water is “clean”, the penalties for allowing leakage are weak, and it is only now becoming a global warming issue as people realize that energy is being consumed to pump the chemically treated water into the soil.
Waste water pipes also leak; however, the EPA levies stricter fines for pollution of waterways by sewage, and can put water companies under consent decrees if they fail to reduce the leakage over time.
Oil and gas pipelines that leak, cause much more pollution, and because they are flammable substances, the consequences of failure often include injuries, severe property damage, and loss of life. Consider the protests against new O&G pipelines that are occurring today … mostly driven by the relatively poor record of pipeline failures. Yet, considering the amount of product that flows through these pipelines, they are still the safest and most cost-effective means of transport.
In the pulp, paper, and potash industries, pipelines are used to transport raw water for the plant feed, salty water from solution mining techniques, and effluent for disposal deep underground. These are all processes where leaky pipes are not an option, and many owners opt to replace pipes after they have leaked several times, even if that decision is mostly to save face from the bad press that results from a pollution event.
PICA (Pipeline Inspection and Condition Assessment) Corp., offers several NDT methods to detect weaknesses in metal pipelines. In our 20 years of experience inspecting pipelines in the applications mentioned above, there is one fact that we have found to be common to all: corrosion is usually highly localized and can be fixed cheaply if you know where it is. In fact, we have noted that the majority of pipelines have only one per cent to four per cent of their length that needs immediate attention (i.e. it is leaking or is about to leak). Figure 1 shows the results of an inspection of a pipeline that is 1,100 feet long. Note that there are three areas that have through-holes that need immediate attention to avert leaks. The rest of the pipeline is perfectly serviceable for many years with no need for any maintenance (although installing a cathodic protection system would further lengthen the life of the pipeline). In Figure 1, the Y-axis is remaining wall thickness, and the X-axis is distance down the length of the pipeline. The small dots are individual, localized pits that are progressing through the pipe. Note that there is a fair length of pipe with no pits at all!
PICA’s in-line inspection tools provide high-resolution readings of the pipe’s remaining wall thickness. Readings are taken every 0.100 inches along the length of the line, and in hundreds of locations around the circumference. This allows PICA to report the axial position, clock position, depth and length of defects exceeding 20 per cent in depth. Figure 2 shows a typical in-line inspection tool. These tools can be tethered for short lengths, or free-swimming for length of up to 30 miles, and are introduced into the pipeline through “pig launchers” and receivers.
If access to the pipeline is restricted, or if it cannot be shut down for a short time for the inspection, PICA offers an external technique that can be used to scan short lengths of pipeline. In some cases, this technique can be coupled with guided wave ultrasonics to interrogate up to 300 feet each way from an access point. Figure 3 shows PICA’s bracelet probe being used to inspect a sewer line.
Now that inspection techniques like these are commonly available, it is important for asset managers to learn of what they offer, and consider the cost of running a survey. Usually the costs of the survey and the local repairs are less than 10 per cent of replacement costs.
In the past, asset managers had to infer pipeline condition from leak frequency, soil resistivity, pipe age and other in-direct factors. Often, 90 per cent or more of the pipe could have been life-extended using simple repair techniques, some of which do not require the pipeline to be taken out of service (e.g. clamps). One of PICA’s customers reported over $20 million of deferred CAPEX costs by using this suggested inspection and repair technique. The exceptionally detailed information delivered by PICA’s in-line tools allowed the pipeline manager to make good decisions about repair, rehab, or replacement of the pipelines.
In summary, NDT techniques are now available for most industries that employ pipes and pipelines. Capital expenditures can be deferred for years by pro-actively investing in good-quality inspection techniques and focused maintenance.
For more information, contact PICA at email@example.com