by Bernie Price
It’s happened … the announcement that a major portion of your facility is being closed for the foreseeable future. What do you do next?
- Accept the news that your plant is facing an impending plant shutdown. It is not necessarily a “knockout” for the plant or your career. Remember, in the often uneven battleground we now call the global marketplace, just about anything can happen. Be ready to get up and start fighting again.
- Designate responsibility to an individual for writing a list of possible scenarios. The individual should have enough clout to implement the chosen strategy, if necessary.
- Go to the top of the company and request that sufficient funds be made available to execute the initial shutdown and preservation strategy.
- Choose the right type of long-term equipment care-takers. Those selected are often security or ex-supervisory types rather than experienced operator/craftsmen with intimate knowledge of the equipment.
- Don’t allow critical components to be pirated (stolen for use elsewhere) if part of a larger plant.
- Remove all process materials. Even innocuous materials left in the unit in the long-term will likely cost five times more than at the initial shutdown. The current operations people are familiar with all the hazards.
- Seek expert advice on equipment preservation resulting in not getting the best bang for the buck.
- Involve the hourly workforce in the shutdown and mothball plan. Almost unbelievably, our recent experience has been that if the decision to shut down at some future date has been made, then involving operators and mechanics can very much improve both the quality of the shutdown plan and its execution.
- Not only record but clearly and physically mark what has been done to preserve the item of equipment during deactivation. The reactivating crew (probably a different group of people) can easily miss that a filter, line blind, internal component, etc., has been removed or added with serious consequences at a future start-up.
Note: In our experience, idle plants with small crews operating at a very relaxed tempo can be dangerous places. Make sure safety programs and routine audits are kept active to avoid accidents.
Just as with any critical situation, a long-term strategic approach coupled with a series of medium-term tactics and detailed plans are needed. You should also consider how long the shutdown is probably going to last (guesstimate) and whether or not the plant will most likely be: (a) restarted, (b) sold as a complete unit or (c) sold piecemeal.
Consider every item or class of equipment individually and write a specific initial storage/mothball technique plus a methodology for ongoing maintenance.
For the purposes of this blog, let’s consider an item of equipment or a whole plant which might restart as early as six to nine months but could also be several years.
It is also a fact that unused plants and equipment – properly prepared for shutdown and left in fairly good condition – can retain much of their value. If, however as is normally the case, a plant is left “as is” and allowed to deteriorate, much of it can be fit only as scrap in just a matter of months. Engaging in a well-planned process of deactivation/mothballing can be worthwhile either way, whether it should ever be reactivated or just sold for its second-hand value at some future point.
None of the products and techniques described is new or experimental. Due to the nature of the environment in which they operate, the U.S. Navy and many oil well drilling contractors have more than 40-plus years of documented experience in the techniques and practices described here.
The materials and equipment you will need
Having a clear view of how the constant foes of galvanic/bio corrosion, mold, mildew, etc., can be mitigated if not defeated is essential. While much will depend on local condition, the wetter and colder situations are much more challenging in terms of handling humidity, while blowing dust is an issue for those in the high desert regions. For this article, we will, however, consider a central United States or European location.
A useful analogy in developing a strategy is to compare what it takes to maintain fire. In the case of fire, it requires the three essential legs of “Heat + Fuel Source + Oxygen”, while in this case, age-related deterioration involves a “Driving Force (such as galvanic action) + a Conducting Medium (electrolyte) + Oxygen.” The fundamental approach to stopping or slowing this age-related deterioration is to remove one or more of the three legs.
In simple terms, we aim to do the following:
- Separate dissimilar metals.
- Protect surfaces which could be attacked, even with a covering of only a few molecules thick.
- Dry out or remove the conducting medium (electrolyte – air or gas). Corrosion cannot occur when parts are stored in environments where the relative humidity is held below 40 percent.
- Remove any oxygen or sources of chemical or biological attack.
The materials we can use are:
- Liquid protective waxes and liquid polyvinyl chloride coating. These can be sprayed on any clean, dry surface to protect them. Wherever it is applied, PVC will form a tough, flexible, waterproof skin that will withstand the extremes of temperature, thermal shock, differential substrate movement, and impingement even when sprayed on webbing to form a cocoon.
- Volatile corrosion inhibitors (VCIs). These generate protective vapors even at room temperatures. They come in a number of convenient forms, including time-release vaporizers, sprays, plastic bags and films, powders, oil additives (VSI), and coatings. They are adsorbed onto the metallic surfaces of the equipment (just a few molecules thick), where they can prevent corrosion for up to two years. While most VCIs are environmentally friendly and create no safety hazards for employees, there are some that are suspected of being harmful. Most contain no toxic substances, such as nitrates, chromates or VOCs (note: volatile organic compounds should not be used in combination with a desiccant).
- Vapor space inhibitors (VSIs). This is an oily concentrate that can be added to lubricating oil systems (internal combustion engines, etc.) when equipment is not going to be completely filled.
- Heat-shrinkable plastic films. These are ideal for enclosing individual machines which have been cleaned, dried and have internal desiccants added.
- VCI-covered polythene films. These are used to wrap individual smaller components.
- Chemical oxygen scavengers. These are frequently added to fresh water used to displace some more corrosive liquid in systems which can’t be effectively cleaned or dried out.
- Chemical inhibitors. These are added to liquids and chemicals and are designed to remove unwanted products while preferentially inhibiting their attack on the body of the container. (Anti-freeze sometimes used in this process contains them.)
- Desiccants. These include numerous substances (solids) which absorb water from gases (air) or liquids.
- Biocides. These are used to prevent microbial growths in water and fuels such as gasoline and diesel fuel.
- Light waxes (in CFC propellants). These are used as surface protectors for metals.
- Sacrificial Anodes. These are used in tanks which cannot be drained of their contents.
The primary pieces of equipment are dehumidifiers. These are available in two forms – those that work on the refrigeration principle and those that use two-cycle rotary (wheel) heated desiccant absorption.
Some Suggested Outline Strategies by Equipment Class
Before considering individual techniques, make a best guess of the duration and whether it is going to be either an “attended monitored” lay-up or a “walk-away” lay-up. This article is a guide and is not intended to be totally comprehensive and detailed.
Tanks and Pressure Vessels and Pipework
In all cases, it is essential that the tanks and pressure vessels and pipework be left as clean and dry as possible. Insert line blinds to create manageable zones that can be slightly pressurized (0.5 psig+) using nitrogen or dry air. Include some small flow and arrange for some simple telltale mechanism to show pressure flow and the level of humidity (indicator cards).
For large enclosures, use a commercial dehumidifier of an appropriate capacity. For vessels, tanks and containments which must be kept full of liquid, some form of oxygen scavenger or anti-biological growth chemical is used (see boilers). If a pipework system contains any traps, have its internals removed and clear all strainers.
Boilers can be laid up using either the long-term dry method or the hydrazine wet lay-up method, which involves leaving the wet side – boiler, economizer and super heater – full of feed-treated water. The feed water is dosed with 15 percent hydrazine, a proprietary solution, and then pH adjusted to raise the alkalinity to a minimum pH of 8.3. The fire side is supplied with heated air with desiccant as a backup.
Both water-side and fire-side points should have new gaskets, except for furnace hot air entry inspection and exit points.
Pumps, Engines, Compressors and Machinery
To minimize internal corrosion, close off all vents and openings, and completely fill the casing with the manufacturer’s recommended lubricant. Alternatively, add volatile corrosion inhibitor in the correct proportion to the lubricating oil.
For large compressors, turbines, etc., first centrifuge/circulate the existing oil using a portable filtration cart through water-absorbing filter elements to remove any free water.
For diesel and gasoline engines, drain the fuel systems and add biocide to the remaining fuel.
To prevent external corrosion, if unpainted, one of the recommended spray-on coatings should be used (either a light wax or liquid PVC).
Maintaining the driest possible conditions for both electronics and external field devices – including sensors, transmitters and valves – can be achieved by strategic placement of desiccant packages and sealing the enclosures. This should be supplemented by placing small containers of VCI powder wherever possible. These will not adversely affect electronics.
Instruments that would normally be in contact with the process materials should be removed, cleaned, protected and marked for immediate local storage.
Seal and insert bags or wraps – desiccants and containers of volatile corrosion inhibitors.
Alternatively, heat using individual strip or built-in heaters.
Motors and Generators
Clean the exterior, grease and apply protective covering. If completely sealed, add packets of desiccant.
Lift carbon brushes from commutators/slip rings.
Where sleeve-type bearings are fitted, VSI concentrate should be added to the lubrication system.
Exercising and Monitoring
Depending on the time involved, it will be necessary to periodically – nominally monthly – exercise equipment by rotating it several times and leaving it at a different (90-degree) angle. Where humidity controls have been set, these need at least weekly monitoring. Where chemical controls are used, these should be checked at three months. Periodic monitoring of motor/generator internal resistance (meggar), as well as tank oxygen levels and humidity levels, are necessary for long-term lay-up.
Don’t forget that, in most cases, various fire protection systems and alarms still need to be maintained and powered up. Fires are common in dried-out cooling towers. If batteries are normally used, disconnect them and smear the terminals with petroleum jelly.
Vented-type lead-acid batteries should first be fully charged, then drained and flushed with distilled water.