- Buyer's Guide
It’s happened … the announcement that a major portion of your facility is being closed for the foreseeable future. What do you do next?
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 the plant will most likely be restarted, sold as a complete unit or sold piecemeal.
Examine 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 article, let’s consider an item of equipment or a whole plant that might restart as early as six to nine months but could also be several years.
Unused plants and equipment that are properly prepared for shutdown and left in fairly good condition can retain much of their value. However, if a plant is left “as is” and allowed to deteriorate, as is normally the case, 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.
Having a clear view of how the constant foes of galvanic/bio corrosion, mold, mildew, etc., can be mitigated if not defeated is essential. Although much will depend on local conditions, 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 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, there are three essential legs: heat, a fuel source and oxygen. Likewise, age-related deterioration involves a driving force (such as galvanic action), a conducting medium (electrolyte) and 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:
The materials we can use are:
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.
Before considering individual techniques, make a best guess of the duration and whether it is going to be an “attended monitored” lay-up or a “walk-away” lay-up. This article is simply a guide and is not intended to be totally comprehensive and detailed.
It is essential that tanks, 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 that must be kept full of liquid, some form of oxygen scavenger or anti-biological growth chemical can be 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 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.
To minimize internal corrosion, close off all vents and openings, and completely fill the casing with the manufacturer’s recommended lubricant. Alternatively, add a 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 normally would be in contact with the process materials should be removed, cleaned, protected and marked for immediate local storage.
Seal and insert bags or wraps of desiccants and containers of volatile corrosion inhibitors. Alternatively, heat using individual strip or built-in heaters.
Clean the exterior, grease and apply a protective covering. If completely sealed, add packets of desiccant. Lift carbon brushes from commutators/slip rings. Where sleeve-type bearings are fitted, a VSI concentrate should be added to the lubrication system.
Depending on the time involved, it will be necessary to periodically 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 every three months. Periodic monitoring of motor/generator internal resistance, as well as tank oxygen levels and humidity levels, is necessary for long-term lay-up.
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.
A recent discussion with two major plant-dismantling/second-hand equipment vendors revealed that currently there are very few people looking for used equipment, and many idle plants are being offered for sale. They reported that when the decision to shut down comes, most companies remove anything that could present an immediate danger but essentially close the doors and walk away from millions of dollars’ worth of equipment.