Grain bin maintenance: detecting and preventing potential failure
April 01, 1994
by Teresa Acklin
Part one of two: common items require routine checking to assure bin safety and longevity
By Harmon L. Towne, manager of engineering for Brock Manufacturing in Milford, Indiana, U.S. Mr. Towne is a registered professional engineer and serves as technical vice-president for the American Society of Agricultural Engineers. This article was first delivered at the 1993 International Technical Conference and Exposition of the Grain Elevator and Processing Society.
For more than 40 years, galvanized, corrugated bins have been built to store grain at commercial elevators. During this period, thousands of these bins have been put to use throughout the world.
Because the bins are constructed of galvanized steel, many people have the misconception that they will last forever. But even galvanized steel tends to deteriorate over a period of time if not cared for properly.
While it is true that under normal conditions these bins will give many years of satisfactory service, it is always prudent, as with any type of equipment, to have general maintenance and inspection as an ongoing part of your operation . A number of items should be checked as part of the routine maintenance in day-to-day operations to locate any possible hazards that may be developing. Many of these same principles can apply to any welded or bolted steel bins, and some principles can even apply to concrete storage facilities.
Many of these maintenance items are ordinary common things that normally would be remembered but sometimes the generality causes us to become lax about maintenance and checking.
Suggestions have been made on possible safety precautions and remedies to use when certain hazards are recognized. But these are not the only things that should be checked, nor are they the only safety measures or precautions that should be considered. Each facility should set up its own maintenance and safety plans to make sure that regular checks are made and that the proper methods of correcting any hazards are used.
When repairs are required that go beyond the scope of the facility's normal maintenance procedures, only qualified individuals with proper equipment should be hired to perform the work. It should be remembered that you are dealing with a silo that must retain its structural characteristics in order to perform the function of storing grain.
Many of the failures we observe in corrugated bins are vveather-related, and because of the nature of the structure, little can be done to protect against the unusual weather situation. But properly designed and installed bins will withstand the normal weather conditions.
The hurricanes that swept through South Carolina in the U.S. in 1991 destroyed about everything in their paths, yet many cases were reported of grain bins being the only items left standing. This indicates that, with proper design and erection, grain bins will withstand even very unusual weather conditions.
THE BIN ROOF.
While one may not necessarily be up on top of the grain bins every day, there are times when individuals are walking across catwalks, checking downspouts and doing various functions on top of the bins. When workers are in these positions. they should always take just a few minutes to look down at the roofs of the bins to see if anything appears unusual.
One of our greatest concerns as manufacturers is the placement of non-galvanized equipment across the top of the bins. As the equipment begins to rust, rain will cause the bin roof to dliscolor with rust as well.
General maintenance dictates that all non-galvanized items should be regularly cleaned and painted. If rust starts showing up on the grain bin roof, the roof should also be painted to prevent any deterioration that can take place.
It also has become common practice in many elevators to use the roof as the support mechanism for the catwalks and cross conveyors. When properly done with the manufacturer's approval, there should not be any problems.
But sometimes the roof is not capable of taking the loads, or proper support mechanisms are not installed, and you can see deflections in the roof caps or roof panels. When this occurs. the loads must be transferred properly to the roof structure or to other support structures to eliminate the possible total collapse of the roof.
Another common practice today is to use temperature cables in the larger bins. Most grain bin roofs can support temperature cables if proper systems are installed.
When looking at the roof ribs, it is fairly easy to see whether problems are being created by the temperature cables. If one sees buckling, the temperature cables should be released, and proper support systems should be placed in the bins to eliminate the potential of pulling in the roof.
Most bins are equipped with some type of roof ladder or stairs to enable movement from the peak to the inspection hatch at the sidewall. Various methods are used, but amone the most common is one with some type of rung bolted on the roof ribs.
If this method is used, an individual doing up or down the ladder should check the connections carefully to make sure the bolts are not pulling through the rungs.
On most of the newer bins, stairs or handrails are installed. This system improves the safety for workers making their way up and down the bin roof.
But these parts are also made of steel. and occasional checks should be made to make sure that the connections are not rusting or loosening. This is a fairly simple check that can be done by observing the system carefullv while walking.
BOLTS AND LADDERS.
Access to the bin roof may be accomplished by a ladder and cage system on the outside of the bin or by some type of manlift in the elevator going to the catwalk. If access is by an outside ladder, individuals climbing the ladder should make regular visual inspectlons.
Obviously, it is important to observe the proper techniques of climbing the ladder. But it is not difficult to stop occasionally and check the bolts in the bin. If holes, rather than bolts, appear at certain locations, the situation immediately should be checked further.
If holes are found, observations should be made while walking around the bin to see if any bolt heads are on the ground. If not, a determination should be made as to whether the bolts were ever there in the first place, as improper or poor erection could be the cause.
Although all bins are designed with a certain degree of safety factor for bolted connections, sheets that do not have all their bolts can cause problems. Any missing bolts should be replaced immediately unless the manufacturer indicates otherwise.
If bolt heads are found on the ground, the situation also should be addressed promptly; either the bolts are of inferior quality or not sufficiently strong, or some other problem is developing. The bin manufacturer should be contacted immediately so that a representative can check the situation.
While the grain-bin industry has been relatively problem-free in the bolt area, operators must be conscious of this aspect. A few years ago, controversy arose over the use of inferior bolts in many applications. Certainly, it is an area of concern if bolts start breaking.
Various grades or strengths of bolts are used in the industry. One easily can determine what bolt has been used by looking at the head of the hex bolts.
A bolt with three slash marks around the head indicates a grade 8, and one with six marks fairly close together indicates a grade 8.2. The actual strength of these two grades is the same, but they are made from different types of rod.
An unmarked bolt head indicates a grade 2, a type that never should be used in the sidewall of a grain bin. Some bolts have a polypropylene plastic head, and these should be a grade 8.2 bolt.
Proper tensioning of the bolts is also important to maintain the structural integrity of the bin. If the bolts were tightened properly during erection, they should not become loose. But if the bolts are discovered to be loose, they should be marked.
When the bin is empty, the bolts should be tightened to make sure they rive the proper clamping force to maintain the bin's structural integrity. Such tightening also assures a weather-tight seal in the bolt holes; water leakage can cause the grain to absorb moisture and swell, putting undue pressure on the structure, as well as spoiling the grain.
When climbing the ladder on the outside of the bin, the ladder and rung connections also should be checked. Many of the older ladders were made by bolting the rungs to the side rails. Because of age, it is not unusual to see rust around the bolted connections and on the rungs themselves.
If rust is found on any of the rungs, it is advisable to replace them with newer rungs to avoid rung failure from rust. It is also advisable to check the bolt holding the rung to make sure it is not loosening or beginning to pull through the rung slot itself.
The connections between the ladder sections should also be checked. Normally, varying length sections may be bolted together, and the connections are extremely important.
When properly assembled, there is a very smooth transition from one section to the next. But if the fit is not good, one may encounter a rough place as a hand hold when climbing. Ladder sections with smooth transitions are preferable on the side of a grain bin.