When it comes to inventory availability, it's important to have the right parts in like-new condition to best support maintenance operations. The standard used by many is the same method that the Original Equipment Manufacturers (OEM's) and distributors use to store spare parts.
The location where some spare parts are stored is critical to meeting the "ready to use" requirement. Minimizing the effects of temperature and humidity is basic, but the protection of parts against the effects of handling during cycle counts and normal store room movements is also a contributor. When possible, it is favorable to have vendors keep the spare parts on their shelves and use a "Just In Time" delivery agreement for access. When not possible, precautions must be taken. Parts that are not in prime condition for use are just as detrimental as no parts at all.
Table 1 shows several types of parts kept in most warehouses or unit locations that need special attention and the category of environmental hazard for these parts.
For many electrical parts, particularly parts with circuit boards, the three main environmental hazards that need to be guarded against are temperature, humidity and Electro Static Discharge (ESD).
During the last twenty years, the nature of electronics used in running a manufacturing plant has changed through the use of more advanced computer controlled equipment. This equipment relies on the use of printed circuit boards that require a low humidity environment with little fluctuation in temperature. Changes in temperature and humidity can cause the micro connections between the components and the printed circuit board to separate or warp. These components are also subject to short circuits from small amounts of voltage, the source of which can be as small as a micro-discharge from the person holding the part. For this reason, these electronic parts must be kept in their special ESD packages, usually a black bag made of non-conductive material originally supplied by the manufacturer. These parts can be so sensitive that even when ESD parts are removed from their special package, the handling person should be grounded using a specially designed ground strap to avoid ESD damage.
Figure 1 is a picture of a typical electrical assembly properly packaged in an ESD bag and enclosed in a custom fit foam container. All employees should be alerted to "black-bag" parts and the caution required to keep them functional.
Belts and Hoses.
Belts and hoses are subject to degradation over time from the affects of UV light, heat, cold and humidity. Unfortunately, there are no black or silver EDC bags to alert users of belts and few plants accurately date or rotate belts and hoses when aging occurs. Since many of the hoses and belts kept in a store room are an insurance spare, these parts may not have a high turnover. When possible, it is best to allow the part supplier to keep these in their environmentally controlled warehouse. This will ensure fresh parts are available for use when needed. If not possible to keep the parts at the distributors' warehouse, belts and hoses should be stored in an environment that is air conditioned in the summer and heated in the winter and not in direct sunlight. The store room should apply First In, First Out (FIFO) stocking practices so that the oldest parts are used first. In extreme cases, a lifecycle approach may recommend discarding and replacing dated belts and hoses after x number of years. ABB also recommends the use of flat storage wherever possible and hanging storage only with appropriate fully supportive fixtures.
Figure 2 shows properly stored gaskets.
Electric motors offer another possibility for degradation due to humidity, temperature extremes and vibration. All motors should be kept in the same low humidity and stable temperature environment as belts and hoses, but they also require regular shaft turning to avoid low spots on the armature and coils and damage to the bearings from false Brinelling. Motor turning can be managed through the use of tags attached to each motor that show the last turn date similar to the inspection date on a fire extinguisher. Electric motors with horsepower greater than 25 should be kept heated through the use of electric heaters. This will prevent shrinkage and expansion from the effects of cold and heat on any metal parts that have different coefficients of shrinkage during temperature fluctuations.
Figure 3 displays an electric motor stored in a low humidity, heated and cooled warehouse. Note the numbers on the motor used to align and indicate position on the shaft key way after rotation. The date and position of rotation is also noted on the blue tag affixed to the motor. The motor is bolted to a wooden skid to lessen area vibrations and ease movement
It is important to recognize many of the parts kept in a maintenance store room can be subject to degradation and damage from the effects of the environment and improper handling or storage techniques. Keeping unknown defective parts on the shelf for emergencies will compound a break down when the defective part is installed and subsequently removed/replaced because of improper storage. Whenever possible, the use of the distributor's stock should be used as this stock is turned over more frequently than the plants' stores stock. Typically, distributors and manufacturers are more likely to keep parts in their stores under tight environmental and handling controls.
If keeping parts on-site, keep them on-site correctly! Hidden damage is worse than known damage and will cost the site more in the log run.