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Practical approaches to rigorous corrosion protection

Volatile corrosion inhibitor (VCI) technology is designed to be used across oil & gas industry sectors and in many applications.

10/09/2017


Figure 1: Hot layup of risers on a drillship using waterborne VCI fogging and capping with film. Courtesy: Cortec Corp.Corrosion is a persistent challenge in all oil & gas industry sectors: upstream, midstream, and downstream. This is due not only to the corrosiveness of the materials exploited, but also to the harsh environments many structural and equipment assets are exposed to in oil & gas production, transport, and processing.

High costs, safety hazards, downtime, and additional labor result. According to NACE International, total annual corrosion costs in oil & gas production is about $1.4 billion, with roughly $590 million assigned to surface pipeline and facility costs, $460 million to downhole tubing expenses, and $320 million to capital expenditures.

Some aspects of corrosion that could be better controlled are completely overlooked or inadequately addressed. For example, millions of dollars' worth of spare equipment sits idle in gas or oil facilities around the world. Too often, a lack of sufficient preservation technology and expertise leaves these assets at the mercy of harsh outdoor environments.

Volatile corrosion inhibitor (VCI) technology and related methods enable more effective protection. VCIs are typically easier to use and prove more environmentally friendly than many traditional treatments. 

A brief survey

The upstream sector explores for and procures crude oil and natural gas using oil rigs, drill ships, and offshore platforms.

Corrosive attacks come both from the nature of the resources used in drilling and from the corrosive environments in which drilling is performed, including, for example, offshore salt-spray conditions. Practically any metal structure or piece of equipment is at risk for corrosion in these circumstances, from polished bore receptacles and offshore platform caisson legs to valves, pistons, pumps, electricals, and fire extinguishing systems. In addition, market volatility often brings long periods of layup, which put the equipment at risk for corrosion, if not adequately protected.

The midstream sector focuses on oil & gas transportation involving millions of miles of pipeline around the world. Corrosion can start at the pipe-manufacturing plant long before pipeline construction begins. Typically, pipes are left unprotected, or a wax-like coating is used that is challenging to thoroughly apply on internal pipe geometry and equally difficult to remove. Corrosive conditions may worsen as the pipes are transported through different types of weather and, in many cases, undergo salt-spray conditions while being transported overseas topside on ships. On land, some pipeline projects take years to complete, during which time pipes sit in unsheltered pipe yards. Welders coming to couple the pipes together have additional work cleaning any corrosion off the to-be-welded surfaces.

Downstream facilities face similar corrosion problems but often on a larger scale due to the oil & gas volumes involved. Downstream facilities keep spares on hand ready for quick replacement of a failed part. Often, though, spares are stored outside on open racks and subject to corrosion.

Figure 2: VCI molecules evaporate from a source, fill an enclosed space, and adsorb on metal surfaces to protect them from corrosion. Courtesy: Cortec Corp.Thousands of aboveground storage tanks risk corrosion on tank bottoms and need to be protected against possible leakage. Basic facility assets such as boilers, coolers, pumps, valves, engines, insulated pipes, and structural steel are also at risk during mothballing or facility construction. 

Ways to the means

Steps to prevent corrosion are not necessarily difficult, if the proper precautions and proper technology are used. By active vigilance and the use of VCIs, corrosion can be reduced in a cost-effective, often more environmentally friendly manner than is otherwise the case.

VCIs are commonly made of organic salts of carboxylic acids. They work as mixed inhibitors to protect against both anodic and cathodic reactions of a corrosion cell. In use, VCI inhibitor molecules vaporize from a source material until they reach equilibrium in an enclosed space. The VCI molecules are attracted to and adsorb on metal surfaces to form a hydrophobic layer that protects the metal from interaction with corrosive contaminants. When the enclosure is opened, the VCIs will dissipate from the surface, leaving the metal corrosion-free and ready to use. On the other hand, if the space is only temporarily opened and enough source material remains, the protective layer will replenish on the metal surface and protection will continue after the openings are closed again.

Because of their vapor activity, VCIs work in multiple phases. Like traditional contact corrosion inhibitors that are added to liquids, they can dissolve and protect metal surfaces in contact with the liquid, including, for example, the insides of a pipe or tank below the surface of the fluid. VCIs also can protect metal surfaces in the void space above the fluid and at the vulnerable interface where the air and fluid meet.

VCIs protect against micro-corrosion and corrosion creep. Many coatings rely on zinc, chromates, and other heavy metals to work. However, the large particle sizes of these substances leave gaps in the coating that can allow corrosion to start in micro-cavities and more easily spread. VCIs protect against this and discourage corrosion spread if the coating is marred by a scratch or dent.

VCIs can be incorporated into other mediums such as liquid forms for pipes and tanks, powder forms for void spaces, packaging materials for wrapping equipment, removable or long-term coatings, foams, and papers. Versatility allows for a tailored approach that considers length of protection and ease of removal.

Applications in oil & gas

A sound corrosion plan preserves assets in all three sectors of the oil & gas industry. A variety of application methods may be used to develop a spares layup strategy that requires very little labor and time to re-commission. Across all oil & gas sectors, a common application method is equipment shrink-wrapping using polyethylene film containing VCIs. The film is made to different durability levels depending on the indoor or outdoor storage situation. Foaming or fogging are added as needed based on the volume of the space being protected.

Equipment stored in this manner can be unwrapped and re-commissioned relatively quickly, typically without the need to clean off traditional petroleum-based coatings that may be classified as hazardous waste. VCI film can be recycled and in some cases turned into new film. This is useful for standby layup of spare equipment as well as for long-term mothballing of entire plants.

These methods are preferable to traditional layup strategies, such as potentially dangerous nitrogen blanketing or dehumidification systems that require monitoring and a constant source of electricity. 


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