by Cal Chapman

New pipeline construction is going “fast and furious” in the Eagle Ford Shale region, in the West Texas “Wolfcamp”, “Bone Spring” and related shales, and all across mid-America with the Bakken, Niobrara and other successful unconventional oil and gas plays.  Companies who build and operate pipelines must attract customers with product to move, secure the land over which pipeline right-of-ways will be cobbled together, and then construct the pipelines.

What happens when a pipeline runs near a high-voltage AC power line?

When soil resistivity is lower, and the voltage driving current along the AC power lines is high enough, the pipeline acts like the “secondary winding” of a transformer.  It receives AC power from the high-voltage lines by what is called “electrical induction.”  Once that power builds on the pipeline, AC electric current flow is going to happen.  When that AC current finds a place to “jump off” the pipeline to go back to the AC power grid, corrosion holes are created in the pipeline metal.  This is AC-induced corrosion, and it is a severe threat to pipeline integrity.

This induced AC power may even pose safety risks to the welders, laborers, operators and other people building the pipeline!  AC power can actually build up on the pipe as it sits above grade on cribbing.  Any time a pipeline is located in “near parallel” to parallel arrangement with high-voltage AC power lines, even for just a mile or two, a qualified corrosion engineering consultant should be brought in to check the situation.

Risks of AC-induced Corrosion and Voltage Buildups

These risks for AC-induced corrosion and unsafe voltage buildups are significant.  A recent story about a Barnett Shale area worker, directed to do some repair to a chemical injection system for a pipeline’s internal corrosion control system, tells the tale.  The gentleman walked up to a chemical injection point and reached up to close a small ball valve, before changing out some injection equipment.  The AC voltage buildup on this pipeline was so great that, when he touched the valve handle, he was hurled backwards by the jolt of “grounding out” the induced AC power!  From what was passed on, he did not suffer lasting injuries.  But this was way more than 15 volts of induced AC (the maximum “safety” voltage threshold), and a significant current passed through part of his body for the instant he was in contact with both the pipe and the earth.

AC Mitigation Systems Might Be Needed

If the opportunity for AC power buildup on the pipeline is pronounced, then “AC mitigation” systems must be designed and installed.  Similar to electrical grounding and lightning protection approaches, these mitigation systems are specialized in design, construction and monitoring.  Recognizing the need for them is paramount, especially when soil resistivities are low and chemical ions such as chlorides are present in higher concentrations in soils.  A lot of the soils in the Eagle Ford Shale play have this “not good” combination of resistivity and soil chemistry factors.  The same can be said, too, for a lot of West Texas and southeastern New Mexico.

Read this article in the Eagle Ford Shale

Cal Chapman is co-founder of Chapman Engineering, which began business in fall 1988. He is a licensed “Cathodic Protection Specialist” through the National Association of Corrosion Engineers (NACE, now called NACE International), and is a licensed professional engineer in Texas and New Mexico. Chapman Engineering provides cathodic protection, AC mitigation, coatings and corrosion protection specifications, and other engineering services. The company performs environmental compliance, assessment and remedy services in oilfield, petroleum wholesale, and industrial settings. In-house staff includes engineers, geologists, corrosion technicians and environmental scientists. Please contact Chapman Engineering at 800-375-7747.

by Cal Chapman

Corrosion control is always a factor in oilfield work.  Above-ground tanks, pipelines, and all manners of equipment suffer from corrosion, both internal and external in nature.  In South Texas, two interesting physical facts come to dominate external corrosion control needs.

Many areas have shallow soils containing large concentrations of chloride ion.  This comes from salt deposited when ancient ocean shorelines ranged across the region.  High chloride ion content causes aggressive corrosion rates on unprotected steel.  Just as importantly, the sodium and chloride ions, often found with other ions as well, cause the soil’s electrical resistivity to be very low.  The low electrical resistance means high corrosion current flows, which again accelerates attack on unprotected steel.  Pipelines are buried in this soil.  Tanks are set on it.
 
Corrosion protection for these facilities should always include a combination of good coatings, good installation and inspection practices, and well-designed cathodic protection (CP) systems.  Here are some pointers for best practices:

• If constructing bulk above-ground storage tanks (ASTs), put a coating on the bottom plate before field welding begins.  This coating will give partial protection to the finished external bottom of tank.  This reduces the amount of protective electrical current needed.  It lowers capital costs for the CP system, and can greatly reduce a monthly electric bill;
• Avoid putting a plastic leak liner under a bulk tank.  This prevents the installation and use of a “remote” impressed-current cathodic protection system on the tank bottom.  We all intend for the first CP system to be the only one needed – but it doesn’t necessarily come out that way;
• If high-voltage AC power lines are nearby, avoid setting up pipeline rights-of-way in “close parallel” to the AC lines!  With the low soil resistivities, high chloride levels, and good coatings, the AC-induction problem may cause SAFETY ISSUES and aggressive corrosion rates;
• Holiday detection is even more important for coatings inspection on pipelines, tanks, and, really, on any paint job where the metal will be in soil or water contact.  Remember, too, that water gets everywhere, sooner or later;
• Coat the bottom of every steel vessel before it is set – not just a paint, but a better-quality and thicker coating!  Dehydrator units, separators, bulk tanks all may be set on crushed rock or caliche, but chloride ions, sulfide ions, and other ions will move to the metal – just by diffusion – and cause corrosion attack;
• Does produced water get spilled inside containment?  Yes, often it does.  That adds chloride and other ions to the tank pad – bad news.

For those not so familiar with corrosion science, here are a few major themes to keep in mind:

• If we just talk about steel, it is not a “naturally occurring” material.  Iron ore is dug up, then combined in very hot furnaces with coke and other alloying metals.  The resulting steel is then cooled, shaped, and so on;
• A lot of new energy is added in the metal-making process.  As soon as this metal is put into the environment, Mother Nature’s electrochemical processes go to work.  Their goal is turn steel back into iron ore – rust!  The reason?  All that energy put into the making of steel is now available to be taken back.  One physical law is that everything, sooner or later, will be “taken back” to its lowest stable energy content;
• To prevent or slow down that rusting process, every piece of steel should be coated.  No water, either liquid or vapor, should be allowed to contact it.  And there are plenty of other chemicals which may drive the corrosion process, chloride ion being one;
• Finally, in addition to the coatings, cathodic protection should be applied.  Coatings by themselves are not good enough, because there are always defects or holes in them.

Read the original Article in Eagle Ford Shale

Cal Chapman is co-founder of Chapman Engineering, which began business in fall 1988. He is a licensed “Cathodic Protection Specialist” through the National Association of Corrosion Engineers (NACE, now called NACE International), and is a licensed professional engineer in Texas and New Mexico. Chapman Engineering provides cathodic protection, AC mitigation, coatings and corrosion protection specifications, and other engineering services. The company performs environmental compliance, assessment and remedy services in oilfield, petroleum wholesale, and industrial settings. In-house staff includes engineers, geologists, corrosion technicians and environmental scientists. Please contact Chapman Engineering at 800-375-7747.