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Practical approaches to rigorous corrosion protection

10/09/2017


Upstream structural corrosion

Figure 3: Corrosion inhibitor being applied to caisson legs. Courtesy: Cortec Corp.To protect against exterior structural corrosion in the upstream sector, VCI coatings can be used in offshore platform layup projects. These types of coatings protect with a relatively thin film, making them more versatile and reducing labor and materials. For internal structural protection, the addition of waterborne and powder VCIs proves highly effective. In a two-year trial inside an offshore platform caisson leg, a significant reduction in corrosion rate compared to the control caisson leg was demonstrated.

It is important to ensure electricals and electronics are in good working condition, preserved from corrosion. This can be done by sticking a self-adhesive cup filled with VCIs inside an electrical or electronics enclosure. The VCIs escape through a breathable lid and fill the enclosure, forming a self-replenishing protective layer on the metal surfaces. Another option is to spray electrical panels with a VCI-enhanced coating formulated either for indoor or outdoor conditions.

The corrosiveness of downhole drilling operations is well-known. VCIs have been formulated into chemistry that can create a persistent anti-corrosive film barrier in these structures to protect against water intrusion, pitting, and corrosive gases. The VCI components of the chemistry provide additional protection for any portions of the downhole structure not in direct contact with the fluids. It can be used in both sweet and sour conditions, that is, low or high hydrogen sulfide concentrations.

Firefighting systems aboard offshore rigs are another critical point of protection. These systems often rely on water pumped directly from the sea, which is highly corrosive. If corrosion occurs between testing periods, the system could malfunction when it is needed. Systems using VCIs have been devised to protect against corrosion of these critical firefighting devices. 

Midstream pipeline protection

Early corrosion protection of newly manufactured pipes is an important step for maintaining pipelines in good condition from the start. This can be done by fogging pipe internal diameters with a waterborne VCI, capping the ends with VCI film, and coating the outer diameters with a waterborne VCI coating that can be removed or left in place as desired. Weld-site coatings reduce the time and effort welders normally require to obtain a clean welding surface. Coating can be washed off with an alkaline cleaner (preferably containing flash corrosion inhibitors), leaving the welder with a clean surface. The same protection strategies apply to pipes already onsite once cleaned of the typical buildup of dust and debris.

On an in-service pipeline, the technology has the potential to protect the pipe against internal corrosion on 360-deg of the inside diameter as the fluid flows through the pipe. This comprehensive protection potential is due to VCI multi-phase characteristics. A traditional corrosion-inhibiting additive in liquid gas or oil streams would only protect the pipe walls in contact with the oil or gas. Here, protection of the entire pipe-wall circumference is achieved.

Environmentally friendly pipeline casing fillers have been developed that protect the annular void spaces between pipelines and their casings. The gel filler is a unique alternative or backup to traditionally used cathodic protection because it protects with or without the presence of an electrical current. The vapor action allows VCIs to migrate under dis-bonded coatings and provide corrosion protection to inaccessible and recessed surfaces. Development of the method was inspired by the request of a North American pipeline corrosion engineering group. The technology has been patented in the U.S. It also can be used in other tubular structures. 

Downstream strategies

Downstream layup strategies are like those already described for spares layup. Preservation of the many spare parts that may be lying on outdoor racks is an important step to downstream asset preservation. This is a growing trend, and many major oil & gas facilities today are preserving everything from the smallest screws to the largest equipment using films, coatings, emitters, and fogs. When the parts are needed, it is easy to unwrap them, recycle the film, and install or re-commission the parts.

Oil & gas facilities also include aboveground storage tanks that require protection from corrosion on tank bottoms. Risks from corrosion include leakage and environmental contamination but can be countered using VCIs found to be compatible and even synergistic with cathodic protection (CP). VCIs injected beneath the tank bottom work to protect areas not in contact with the CP's conductive electrolyte, while in certain cases the CP may enhance the effectiveness of the inhibitor. VCIs can be added to tank pads before construction or injected below existing in-service or out-of-service storage tanks.

Downstream systems such as piping or electronics benefit from proactive corrosion protection. VCIs can be injected into insulated piping to protect against so-called corrosion-under-insulation. Emitters added to electrical and electronic instrument boxes can be a simple protection against the extra costs of electrical repairs, malfunctions, or downtime. Coatings can be used on a variety of structures and equipment. 

Final words

Corrosion is everywhere in the oil & gas industry. Fortunately, practical methods for protection of assets are available today that were once overlooked. VCIs enable more thorough protection in void spaces using vapor-phase action. They enhance coatings performance by protecting against micro-corrosion, and reduce need for materials that must be disposed of as hazardous waste. Instead, they are typically recyclable or easy to remove and discard. They preserve important assets during common waiting periods prior to construction or when the volatile market warrants layup. They have forged important ground in the layup of equipment for major oil & gas companies globally and will continue to be an important source of providing cost-effective preservation to the industry.

Special thanks to Bob Boyle, Jim Holden, Eric Uutala, and John Wiermaa of Cortec Corp. for their firsthand insights on corrosion in the oil & gas industry.

Julie Holmquist is content writer at Cortec Corp.

For more information, visit www.cortecvci.com or email productinfo@cortecvci.com.


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