Mothballing Requires More Than Idle Thought

Today’s weak global economy is forcing closure and immobilization of plant and equipment worth billions of dollars. Unfortunately, such actions usually are done hastily and typically against a background of acrimony. Even worse, they can diminish or even destroy the value of assets and preclude the possibility of reactivating them once business rebounds.

Two major plant dismantling/second-hand equipment vendors recently told me that when the decision to shutdown comes most companies remove anything that could present an immediate danger and essentially close the doors and walk away from millions of dollars worth of equipment. Leaving assets “as is” to deteriorate can make them suitable only for scrap in just a matter of months. Yet, it’s a fact that an unused plant — if properly prepared for shutdown and left in fairly good condition — can retain much of its value. Engaging in a well-planned process of deactivation/mothballing can pay off whether the intention is eventual reactivation or sale of assets.

In my experience through three boom/bust phases in the process industries and oil well drilling, 75% of idled plants or rigs eventually were reactivated in some form. The bottom line is that while it only should cost 5% or less of Plant Replacement Value (PRV) to reactivate a well-preserved unit, restarting an inadequately mothballed plant will cost 20+% of PRV. This often is a deal breaker.

So here, we’ll look at what should be done and describe specific products and techniques. None of these are new or experimental — there’re 40+ years of documented experience for some.

The Approach
It’s essential to have a clear view of how to mitigate if not defeat the constant foes of galvanic/bio corrosion, mold, mildew, etc. While much depends on local conditions, wetter and colder environments pose greater challenges for handling humidity, while blowing dust is an issue in high desert regions.

A useful analogy in developing a strategy is to consider how plants fend off fire hazards by eliminating one of the fire triangle’s three elements — i.e., heat, fuel source and oxygen. The three corresponding elements for age-related deterioration are a driving force such as galvanic action, a conducting medium or electrolyte, and oxygen. The fundamental approach to stopping or slowing deterioration is to remove one or more of the three.

In simple terms we aim to do the following:
• separate dissimilar metals;
• protect surfaces that could be attacked — with a covering, even if only a few molecules thick;
• dry out or remove the conducting medium (electrolyte — air or gas) (Corrosion can’t occur when parts are stored in environments with relative humidity below 40%); and
• eliminate any oxygen and sources of chemical or biological attack.
Materials and equipment we can use are:

Liquid protective waxes and liquid polyvinyl chloride (PVC) coatings. These can be sprayed onto any clean dry surface to protect it. Light waxes are chosen for surfaces where a subsequent removal process such as high-pressure washing might damage the substrate. PVC will form a tough, flexible and waterproof skin that will withstand temperature extremes, thermal shock, differential substrate movement and impingement, even when sprayed onto webbing to form a cocoon.

Volatile phase/corrosion inhibitors (VPI/VCI). Such materials generate protective vapors even at room temperature. They come in a number of convenient forms, including time-release vaporizers, sprays, plastic bags and films, powders, oil additives (see VSI below) and coatings. They are adsorbed (just a few molecules thick) onto metallic surfaces of equipment and can prevent corrosion for up to two years.

They actually have surprisingly low vapor pressures and are solid or liquid at room temperature. While there are many chemical compounds in use, the most common form of VPI is a salt of an amine (e.g., the carbonate salt of dicyclohexylamine) and a weak acid. Research has shown that they work by disassociation of the amine and the acid; the two volatile components then recombine on the metal surfaces.

While most VCI are environmentally friendly and create no safety hazards for employees, some are suspected of being harmful. Most contain no toxic substances such as nitrates, chromates or volatile organic compounds (VOC). (Note: products containing VOC shouldn’t be used in combination with a desiccant.)

Vapor space inhibitors (VSI). These concentrates can be added to lubricating oil systems (internal combustion engines, etc.) when equipment isn’t going to be completely filled. They essentially boil at ambient temperatures to exclude air, leaving an oily residue.

Heat-shrinkable desiccant plastic films. Such films containing desiccants are ideal for enclosing individual machines that have been cleaned and dried.

VCI-covered polyethylene films. These suit wrapping individual smaller components.

Chemical oxygen scavengers. These compounds are added to fresh water used to displace more-corrosive liquid in systems that can’t be effectively cleaned or dried out.

Chemical inhibitors. Incorporated into liquids, they remove unwanted products while preferentially inhibiting their attack on the body of the container. (Anti-freeze sometimes used in mothballing contains them.)