Dehumidifiers. Such equipment removes moisture by one of two methods, the refrigeration principle or two-cycle rotary (wheel) heated desiccant absorption.
You must couple a long-term strategic approach with a series of medium-term tactics; detailed plans are needed. First guesstimate how long the shutdown is probably going to last and whether the plant most likely will be restarted, sold as a complete unit or disposed of piecemeal.
Consider every item or class of equipment individually and detail a specific initial storage/mothball technique plus a methodology for ongoing maintenance.
The individuals doing the initial deactivation often aren’t those who’ll be doing the reactivation — so encourage them to visibly identify various components and equipment state, even if this is just by using chalk or felt tip pen.
Before we go further into mothballing, permit a small digression about the practice of “pirating parts” from an idle unit. It can wreak havoc or worse. I vividly recall the impact on a major U.S. chemical manufacturer I was involved with. After it shut down a product line in the 1960s, other operations on site began to purloin parts. When the market recovered four years later, little of the plant was left to restart. The company was forced to exit the market for that product. So, in your preservation plan explicitly prohibit removal of parts.
Now, let’s get into how to properly deal with specific equipment and hardware. For purposes of this article, let’s consider a plant in the central U.S. or Europe that could restart in from six to nine months to perhaps several years. What follows is only a guide and isn’t intended to be comprehensive and detailed.
Tanks, pressure vessels and pipework. In all cases ensure these are 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. Provide a small flow and arrange for some simple telltale mechanism to show pressure, flow and level of humidity (e.g., indicator cards).
For large enclosures, use an appropriate-capacity commercial dehumidifier or maybe even consider a total “tented” enclosure. For vessels, tanks and containments that must be kept full of liquid, employ some form of oxygen scavenger or anti biological growth chemical (see Boilers). If a pipework system contains any traps, remove their internals and clear all strainers.
Boilers. These can be laid up using either long-term dry or wet hydrazine methods. The latter involves leaving the wet-side — i.e., boiler, economizer and superheater — full of treated feed water (dosed with 15% hydrazine, a proprietary solution, and then pH adjusted to raise alkalinity to a minimum pH of 8.3) and supplying the fireside with heated air with desiccant as a backup.
Both waterside and fireside 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 VPI in the correct proportion to the lubricating oil.
For large compressors, turbines, etc., use a portable filtration cart with water-absorbing elements to remove any free water in existing oil soon after shutdown.
For diesel and gasoline engines, drain fuel systems and add biocide to remaining fuel.
To minimize external corrosion, spray either a light wax or liquid PVC on unpainted surfaces.
Instruments and controls. Maintain the driest possible conditions for both electronics and external field devices, including sensors, transmitters and valves, by strategically placing desiccant packages and sealing the enclosures. Supplement this by putting small containers of VCI powder wherever possible — they won’t adversely affect electronics.
Instruments that would normally be in contact with process materials should be removed, cleaned, protected and marked for immediate local storage.
Electrical enclosures. Seal and insert bags or wraps — desiccants and containers of VCI. Alternatively, heat using individual strip or built-in heaters.
Motors and generators. Clean exterior, grease and apply protective covering. Lift carbon brushes from commutators/slip rings. Where sleeve-type bearings are fitted, add VPI concentrate to the lubrication system. Include packets of desiccants if completely sealing a unit.
Periodically — nominally monthly — exercise equipment by rotating it several times and leaving it at a different (90°) angle. Where humidity controls have been set, monitor these at least weekly; where chemical controls are used, check these every three months. In addition, long-term lay-up requires reqular monitoring of motor/generator internal resistance (meggar), as well as tank oxygen and humidity levels.
Auxiliaries. Don’t forget that in most cases fire protection systems and alarms still need to be maintained and powered up — fires are common in dried-out wooden cooling towers. If batteries normally are used, disconnect them and smear terminals with petroleum jelly. Fully charge vented-type lead-acid batteries, then drain and flush them with distilled water.
Don’t Squander Assets
It makes sense to think strategically about plant deactivation. Proven techniques can preserve the functionality and value of assets. Proper mothballing can pay off substantially whether an operating company aims to eventually restart, sell or dismantle a plant.
Bernie Price is CEO of Polaris Veritas Inc., a Houston-based consulting group. E-mail him at Polarisver@aol.com.