October 2016, Vol. 243, No. 10
Features
Cleaning, Maintaining, Inspecting all Part of a Day’s Work
Cleaning, maintenance and inspection are crucial to a pipeline’s effectiveness and profitability. There are 3.5 million kilometers of oil and gas pipelines around the world, dating back to the 1870s – the oldest of which is in the United States.
Today, the United States has 2,225,032 kilometers of pipelines in operation, of which, 1,984,321 kilometers is dedicated to transporting gas, according to the Central Intelligence Agency (CIA) Factbook.
It is, therefore, unsurprising to discover that in the United States, in 2015 alone, there were 27 gas transmission pipeline accidents and repairs to about 8,000 corrosion leaks reports the Energy Information Administration (EIA) that year. Corrosion, is the number one cause of pipeline failure in the United States, according to the insurance industry’s Claims Journal, August 2016.
About 63% of natural gas transmission accidents were caused by internal corrosion and 36% were due to external corrosion. Corrosion can also have serious consequences. For example, in late April, a corroded weld on a Texas Eastern pipeline in Westmoreland County’s Salem Township exploded severely burning a man, destroying his house, charring cars and melting a road, reports Natural Gas Intelligence, April 2016.
Why is Cleaning Necessary?
Time, deterioration and corrosion are the enemy of safe pipeline operations and the environment. Pipeline failures cost money for clean-up and unscheduled downtime due to repairs and maintenance. Not surprisingly, pipeline failures have resulted in government regulations, such as the Department of Transportation (DOT) Pipeline Safety Regulations in the United States and the HSE Pipeline Safety Regulations in the United Kingdom, which require regular pipeline inspections.
Cleaning pipelines not only helps prevent corrosion but also reduces the build-up of a host of deposits, such as salts and scales, corrosion products (including black powder), paraffin wax, asphaltenes, hydrates, sand and well fines, napthenates, emulsions, sludge and water. Many of these deposits come from the transported fluids, while others are caused by chemical reactions between fluids and system metallurgy, or result from a combination of different fluids in transport lines.
Regardless of origin, pipeline deposits cause problems such as increased backpressures, decreased flow, reduced system reliability and the risk of full or partial blockage. As a result, product quality is reduced, operational expenditures rise and, correspondingly, profits fall.
Cleaning Pipelines
Mechanical and chemical cleaning are the two main ways to clear pipelines.
Mechanical cleaning involves a pig, or mechanical gadget designed to fit inside and travel along an oil or gas pipeline to carry out a variety of maintenance and inspection tasks. In its cleaning mode, the pig is repeatedly sent through the pipeline to sweep up deposits until hardly any is left behind.
However, this doesn’t necessarily mean the pipe is completely and perfectly clean since the action of the pig can spread a thin layer of deposit on the inside walls, or it can result in the deposit layer being ground into sub-micro particles. This can lead to a problem downstream and may even promote corrosion, caused by harmful material being trapped under the compacted deposit layer.
New technology, in the form of intelligent pigs with magnetic flux leakage and optical inspection including, sophisticated 3-D, almost visual inspection, can eliminate the problem of the residual trail left by mechanical pigs. Modern intelligent pigs, equipped with sensors, can establish when the pipe is clean, thereby eliminating wasteful re-runs. Intelligent pigs can also inspect the state of the bare steel. Notwithstanding the high-tech approach, there are still instances of inspection companies finding the presence of deposits after cleaning.
Chemical cleaning involves the use of liquid cleaners mixed in water, diesel, methanol or iso-propyl-alcohol to form a cleaning solution that can be pushed through a pipeline by a mechanical pig. Pipeline cleaning chemicals are normally of a neutral pH, with deposit permeating and penetrating capabilities, designed to remove soft and hard wax deposits and to maintain, restore and enhance pipeline flow capacity.
Chemical cleaning is also essential to remove crude oil deposits and prevent contamination when a pipeline is being converted to carry refined oil product or gas and vice versa. For example, TransCanada’s Energy East project, which is converting an existing gas pipeline into a crude pipe linking the Alberta oil fields to markets in Eastern Canada and beyond needed chemical cleaning to prevent contamination.
Chemical cleaning with an appropriate substance, after a pig train operation, provides explosion-safe conditions for using flame-cutting and welding equipment for replacement of pipes, making the operation significantly quicker, cheaper and safer.
Top Cleaning Challenges for Pigs
Cost, labor intensity, pig fallibility and pig unsuitability in probably 40% of the pipeline network are the four industry-wide cleaning challenges. The pipeline cleaning process is not cheap. One industry expert has suggested that it costs in the $210,000-$250,000 range, plus a disposal fee of $25,000-$30,000 to chemically clean (with a cleaning pig) a 24-inch, 15-mile gas pipeline in preparation for an ILI smart pig operation that costs another $100,000.
Therefore, the total pigging cost on a 15 miles of pipeline would be between $335,000 and $380,000, or about $35,000 per mile. RBN Energy estimated that based on a standard pigging operation of $35,000 per mile, cleaning the entire U.S. pipeline network just once would cost $59 billion at 2013 prices!
In addition, the pigging cleaning process is labor intensive for an “in-service” pipeline requiring lots of careful planning and preparation. Each pig launch needs two or three man-hours of preparation, and some pigging projects require 50-60 launches or more. A typical pigging system requires the opening or closing of at least three major valves, the draining and venting of a barrel, and the opening and closing of a closure door.
In some cases, it can take up to four hours for a single crew to load and launch a single pig, excluding the time taken to receive and remove the pig. Moreover, a pig can only operate for a few kilometres at a time. The process is slow, can be messy, and may cause problems for downstream equipment if filtering is inadequate.
Cleaning pigs generally go hand-in-hand with smart pigging programs but smart pigs are not infallible. While smart pigs can spot corrosion and potential areas of concern, pinholes or corrosion that is less than 1 cm in size may be missed. Moreover, if a cleaning pig doesn’t thoroughly clean the pipe in preparation for the smart pig, those “misses” multiply.
Finally, not all pipes are piggable. Of the 2,225,032 kilometers of pipeline in the United States, roughly 30% is categorized as “un-piggable” and 10% is considered “difficult to pig.” Therefore, about 40% of the total network is probably unsuited for cleaning and inspection pigging.
Common obstacles to pigging operations include lack of entry points, multiple pipe diameters, impassable valves or fittings, pipe bends, external pipe defects and obstruction caused by contaminants.
“To navigate challenging pipeline systems, bespoke designs will continue to be used to overcome bore changes and restrictions,” said Cara Low of Jee Ltd. “There is likely to be an increase in the use and number of innovative cleaning designs.”
Big Business
Cleaning, maintaining and inspecting pipelines is big business. There are a wide range of companies providing such pipeline services, including leading players such as Enduro, Jee Ltd and T.D. Williamson. The sector is likely to grow, as pipeline integrity regulations become more widespread and toughened, together with the need to further improve the cost-effectiveness of pipeline operations due to the current depressed energy prices.
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