Is your silo plugged? Bridged or Caked?
Storage silos are used in almost every industry to store materials safely until they are needed for use, but no matter the design or the materials stored, silos are susceptible to material flow issues caused by blockages. Blockages not only lead to a reduced storage capacity and disrupted or slowed operations, they also promote bad flow characteristics. When material flow is off, delamination, exterior concrete cracking and structural failure can result. There are numerous blockage types possible in storage silos, two common flow issues are bridging or caking. If there is a blockage and your silo is plugged, here's how to know whether it's related to bridging or caking. Bridging When material is poured into the storage silo it exerts pressure on the material under and around it, and with some materials, this surrounding pressure can cause a structural bond. This bond results in a bridging effect, where the bottom of the bridge empties but a dome arch remains, preventing any further material from flowing. As more material is dumped on top of the bridge the pressure exerted increases and the bonds holding the bridge together will actually become stronger. Caking Caking occurs when powder, such as detergents, fertilizers and salts, become cohesive after storage, forming agglomerates comprised of individual particles that are bonded together. Caking results when the magnitude of interparticle forces increase over time. The most common cause of caking is moisture migration due to temperature changes with materials that are soluble. Caking creates resistance to flow in silos and can result in residue on walls. You can help reduce the likelihood of material build-up through a number of ways, click here to watch and learn more. Depending on how easily stored material compacts or hydrates, your silo may need to be completely emptied on a regular schedule as often as once a month or as little as every year. Silos that are regularly emptied and refilled are less likely to experience build-up issues than in those kept topped off. Regularly emptied silos need professional cleaning less frequently in comparison. They are also less likely to experience issues like compacting and hydrating. Hydration occurs when moisture mixes with stored materials and causes them to solidify within the silo. When this happens, materials can expand and cause added wall pressure, increasing the likelihood of structural failure. The routine examination of your silo is only effective in increasing facility safety and ensuring smooth operations when it is conducted in conjunction with professional cleaning and inspection services as part of a regular preventive maintenance schedule. Whether you have bridging, caking or plugging of any stored material, it’s essential to contact USA Silo Service, a division of the Marietta Group, which includes Marietta Silos and Marietta Inspection Services, to have the build-up removed quickly. This recent case study shows USA Silo Service using their proprietary equipment and cleaning methods to remove coal build-up in a silo and greatly improve material flow. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on our .
Why Silo Diameter Determines the Construction Method
The two most common systems for constructing a concrete silo are Jumpform and Slipform. Concrete storage silos from 10' to 65' in diameter can be built using the Jumpform technique, while Slipform silos are best for construction projects over 65' in diameter. Jumpform construction is one of the most flexible silo construction methods available in the industry today. So is the Slipform method. There are absolutely no shortcuts to either method because safety and performance remain at the forefront of every silo project. So, what determines the construction approach? Jumpform construction is not as time sensitive as Slipform. Jumpform is completed in stages, offering some economies of scale associated with equipment installation, reinforcing steel assembly, rebar inspection and concrete pour to cure. Jumpform can be the most economical construction choice. The form can be set-up and ready to make the first pour of concrete within a week. Because Jumpform is poured in increments, pour costs can be reduced by as much as 20% over Slipform construction where a continuous pour is required. The Jumpform silo framework is reusable. It takes just a few days to set up after delivery to the job site. This form provides a safe, circular deck to access and erect the silo from the interior, creating a smaller job site footprint. When construction is finished, the form is quickly removed from the job site. Marietta Silos' standard Jumpform horizontal construction joint detail creates a leak-proof joint system and is the best choice for concrete storage silos less than 65’ in diameter. Jumpform silos are poured in multiple sequences as opposed to a single sequence in the Slipform method. Therefore, an allowance in the time schedule permits a thorough quality control inspections of the Jumpform, steel reinforcements and embedments. Only then is the concrete segment poured. Marietta Silos is the only Jumpform manufacturer in the country that complies with OSHA 125' scaffolding requirements. While Jumpform is an ideal method for building concrete silos less than 65' in diameter, Slipform construction offers many advantages in larger scale silo design and construction; these are described separately. To learn the step-by-step Jumpform process and to understand its efficiencies, watch our Jumpform silo video. Check out our full library of silo inspection videos on silo maintenance, inspection and repair on our .
Silo Inspections are the New Normal
Prevention is the most effective method to ensure the integrity and continued operation of your silo. Regular maintenance and inspections can increase the life of your silo and ensure the safety of those working around your structures. Though frequent inspections should be conducted in-house to catch warning signs early on it is important to understand the accompanying limitations. Many serious issues can only be identified by experienced silo inspectors or silo engineers during in-depth examination of empty silos free from material buildup. The routine examination of your silo is effective in increasing facility safety and ensuring smooth operations only when it is conducted in conjunction with professional inspections as part of a regular preventive maintenance schedule. When used in place of professional services, in-house inspection, cleaning, and repair procedures increase safety risks. Failed silos can sometimes be repaired and some stored material can be recovered. However, companies often face additional costs from cleanup, possible environmental damage, injury, or loss of life. While working on welding and fabricating metal bins for a concrete silo in December 2016, a fire broke out and resulted in the death of one crew member. After determining the crew did not have the required confined space permit, a general negligence action was settled for $1.75 million. (Michigan Lawyer Weekly, April 2017) In August 2013, employees at an Ohio-based concrete facility attempted to remove material buildup of fly ash clumps in a clogged silo. After cleaning attempts of the interior using “a metal bar and air hose failed” an employee, who entered the silo without a lanyard and harness, died when a fire erupted. During the investigation, OSHA noted 10 serious safety violations, which resulted in a fine of $55,800. (OSHA News Release, November 2013) Both of these accounts highlight preventable accidents where the necessary confined spaces permit was not held and the workers did not have the necessary safety training. Confined space permits and safety training are essential for safe inspections. While there are no inspection recommendations specific for silos, OSHA does have policies regarding confined space entry that are essential for interior inspections. The effective inspections, however, depend on more than this permit. Inspectors must also have field experience and an understanding of the unique properties that effect silo material flow and structural integrity. Industry experience further enables trained silo and bin inspectors to recommend preventative maintenance to address issues before they become serious problems. Only inspectors with industry experience and proper silo engineering, design, and construction training can anticipate these issues to increase the effectiveness and safety of your silo. It is recommended that you conduct professional inspections at two- to five-year intervals to help identify any issues that could lead to structural failure. Silo inspections should include examining the main aspects known to be potential areas of failure. These inspections should include the foundations, walls, cones, discharge configuration, floors, shelves, tunnels, and roofs. The Mine Safety and Health Administration (MSHA) and OSHA have consistently emphasized a focus on silo processing and activity, but in recent years, one of their primary efforts has been on the importance of workplace safety and accident prevention. When it comes to the enforcement of safety policies, if there is an issue within a facility, the MSHA and OSHA are expecting to see a current silo inspection report for reference and assessment. Many insurance companies are also now requiring silo inspections on the facilities they insure. Inspections can uncover problems that require immediate remediation. The most important thing to remember when conducting silo inspections is to consult a professional silo inspection and repair company if you discover anything alarming. You should also defer to a professional inspector if you do not have personnel with the necessary permits for closed space entry. The importance of having regularly scheduled inspections by a professional silo company is even more evident in a recent case study in Florida where multiple discharge asymmetric flow failures were present. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on
Concrete Stave Silos
Concrete stave silos are reinforced with exterior, galvanized steel hoops, which help compress the walls and provide necessary tension for structural integrity. The concrete staves act to distribute the load of the material over the hoops. The hoops are the primary structural stabilizer of the silo and for this reason; it’s essential to inspect the condition of the exterior hoops, as they are vital to the health and safety of the silo. The exterior hoops shouldn’t be bent, broken, falling off, or lying on the ground. It’s also important to make sure the hoops aren’t heavily corroded. Hoops are bolted together with a lug, which can lead to issues if it begins to corrode. The hoops are tensioned to a specific rating and pressure, so it’s essential that the hoop has not been welded to and stands independently. Since stave silo construction utilizes steel galvanized hoops for structural integrity of the bulk storage system, failure to protect these hoops properly will shorten the designed stability of the entire system. A cementitious silo coating is ideal on concrete stave silos, protecting the steel galvanized hoops and preventing leakage. These bonding and waterproofing agents seal the joints between the staves and add a level of corrosion protection to the exterior steel hoops, ensuring long lasting defense against corrosive elements and deterioration. One recent case study examines a concrete stave silo with rusted and broken hoops, showing further evidence that failing to inspect your silo regularly will put your silo’s structural integrity, operability, and safety in jeopardy and require costly repairs in the future. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on
Regular Silo Cleaning: An Integral Part of Maintaining Proper Flow of Materials
Just as routine silo inspections are an essential component of your maintenance program, so too are routine cleanings. Regularly cleaning your silo can help keep it operating efficiently and limit potential liabilities. Regular cleanings also increase your silo’s usable lifespan, minimize big ticket repairs, and avoid more costly cleaning expenses. Silos that are emptied regularly and refilled will not have the same buildup issues as silos that are kept topped off, but every silo can benefit from a regular cleaning schedule. Cleaning your silo can save you money in several ways. The primary savings are in recovering stagnant material that has built up inside your silo. This prevents losing that material and the resources — time, energy, labor — that went into storing it. Depending on your material, cleaning also can help prevent degradation or contamination that occurs when material sits too long, thus reducing or destroying its value. Routine cleaning is necessary to remove the residue buildup inside the silo that reduces the volume of new material that the filled silo can hold. In all silos, cleaning removes old material residue which, in turn, helps maintain the freshness and concentration of the newly introduced material. Every silo, no matter the design or whether it’s steel or concrete, will benefit from a regular cleaning schedule. The benefits of a professional cleaning every year far outweigh the initial costs as this maintenance step keeps your silo running at full capacity, allowing maximum efficiency and leading to more consistent production schedules with no unplanned downtime. Routine cleaning prolongs the life of your silo. Find out more on how to keep your silo clean and why it’s important to have your silo cleaned. To learn more, be sure to check out our full library of videos on silo cleaning, construction, inspection and repair on .
Silo Flow Patterns: What’s the Difference Between Funnel Flow and Mass Flow?
Construction, cone angles, and the type of stored material are all factors that influence how material moves through storage silos. Funnel Flow Funnel flow silos are usually more cost effective to construct, costing between 20-30% less than mass flow silos, but are not suitable for all materials. The flow channel drains material in the middle first. As the silo empties, side material flows into the middle channel. Because of this flow pattern, funnel flow silos that are not emptied completely on a regular basis keep stagnant, or dead, material against the silos walls. Without scheduled emptying, this causes material to build up along the silos walls and leads to issues like ratholing or irregular flow. Taken together, these factors can enhance particle segregation, limit your live capacity, and cause silo failure. Generally, a funnel flow pattern is only suitable for coarse, free flowing, non-degrading solids when segregation is minimal. Learn more about Funnel Flow Silos. Mass Flow Mass flow silos do not experience the same material flow issues as funnel flow silos. Stored materials move down the silo as a column, with no flow channels and the first materials in are the first materials out, providing for a uniform flow. Mass flow is ideal for materials that are susceptible to segregation based on particle size or density, minimized by the first in, first out flow sequence, with the segregated particles remixing as they discharge. It is an ideal flow pattern for coal or other materials that are combustible or perishable. Learn more about Mass Flow Silos. Funnel flow and mass flow are common silo flow patterns. In addition to these two are expanded flow and fluidized flow patterns. Find out more about the different types of concrete silo flow patterns. To learn more, be sure to check out our full library of videos on silo maintenance, inspection and repair on
Is Cement in Your Silo Getting Wet?
The quality of your stored cement can be compromised by the conditions on top of and inside your cement silo. In fact, no matter the design or the materials stored, silos are susceptible to material flow issues. Material flow that is unimpeded by moisture or other issues is essential for smooth operations and the continued functionality of your silo. To prevent stored cement from setting inside the silo due to moisture and humidity levels, the structure must be completely watertight. Even the smallest leaks in silo roofs and walls can damage your stored cement and result in material flow issues. Ambient humidity levels can also cause some materials to set. If you do aerate stored materials, it is essential to use an air dryer system to help lower the ambient humidity level in your silo. You should also avoid over aerating stored materials as excess aeration can pump unneeded moist air into the silo, which may lead to hydration of the cement. Hydrating occurs when moisture mixes with stored material and causes it to solidify within the silo (cement is highly susceptible to hydrating). When this happens, the cement can expand and cause added wall pressure, increasing the likelihood of structural failure. Silo Maintenance Schedules Verify during inspections that regular preventive maintenance measures are being followed. Essential maintenance includes exterior waterproof coatings and keeping your air pad and air stones in good operational condition. Silo maintenance should also include a routine professional cleaning and regular, complete silo emptying. Of these measures, one of the most important is regular emptying. Silos that are regularly emptied and refilled are less likely to experience buildup issues that can be seen in silos that are kept topped off. Regularly emptied silos need professional cleaning less frequently and are less likely to experience problems, such as material compacting and hydrating. The importance of inspecting your silo on a regular basis and making sure your structure is protected from the elements, especially the roof, is the focus of one of our recent case studies, which specifically examines a leaking concrete silo roof, with cement stored inside. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on .
Do You See Cracks In Your Concrete Stave Silo Walls?
Concrete stave silos are constructed using precast concrete blocks, or staves, that interlock. Stave silos are reinforced with exterior, galvanized steel hoops which help compress walls and provide the necessary tension for structural integrity. When it comes to the structural integrity of your concrete stave silo, it’s important to look at the condition of the exterior wall and the exterior steel hoops. When inspecting your stave silo, you want to look specifically for cracks in the staves or bulges in the wall. If you see cracks in the staves, you need to decide what kind of crack you’re seeing. Here are the types to look for – horizontal, vertical, or diagonal cracks – or more severely, when you see an offset and it appears the wall is starting to move. The upper wall is pushing out over the lower wall above a horizontal crack. If you have a crack and it’s starting to move and expand, this is a sign of silo failure and it’s time to call in the experts. It’s equally essential to look at the exterior steel hoops because they maintain the structural integrity of the silo; their stability is vital to the health and safety of the silo. The exterior hoops shouldn’t be bent, broken, falling off or lying on the ground. It’s also important to make sure the hoops aren’t heavily corroded. Hoops are bolted together with a lug and the lug can be problematic if it beings to corrode. The hoops are tensioned to a specific rating and pressure so it’s essential that the hoop has not been welded to and stands independently. One of our recent case studies examines a cracking stave silo and provides further proof on the importance of keeping a proactive maintenance schedule which includes inspecting your silo regularly. Silo inspection is the most effective, preventative method to ensure the integrity of your concrete stave silo. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on
Protect Your Silo from Ratholing and Asymmetric Flow
Buildup in the Silo is an Indication of Ratholing No matter the design or the materials stored, silos are susceptible to material flow issues caused by blockages. Buildup in the silo is an indication of ratholing and potentially asymmetric flow, which can increase pressure loads inside silo walls. When you have buildup in the silo, the loads associated with asymmetric flow can be detrimental to the structural integrity of the silo as they can lead to wall failure and total silo failure. Material flow that is unimpeded by blockages is essential for smooth operations and the continued functionality of your silo. Blockages not only promote bad flow characteristics, but also lead to a reduced storage capacity. You can help reduce the likelihood of material buildup through a number of ways. Depending on how easily stored material compacts or hydrates, your silo may need to be completely emptied on a regular schedule as often as once a month or as little as every year. Cement Silos To prevent stored cement from setting inside the silo, the structure must be completely watertight. Even pinhole leaks in silo roofs and walls damage your stored materials and can result in blockages and material flow issues. Ambient humidity levels can also cause some materials to set. If you do aerate stored materials, it is important to use air dryer systems to help lower the ambient humidity level in the silo. You should also avoid over aerating stored materials. Excess aeration can pump unneeded moist air into the silo which may lead to hydration of the cement. Essential maintenance includes exterior waterproof coating(s) and keeping your air pad and air stones in good operating condition. Completely emptying your silo frequently is also important as it helps prevent compaction of stored materials. Fly Ash Silos It is important to keep the fly ash cool as it is loaded into the silo. Make sure your ash does not include unburnt carbon material as this can lead to material buildup along the silo walls. Chemicals from pollution control chemicals can cause your ash to become cementitious, or sticky. Coal from the Wyoming Powder River Basin is also inherently cementitious in nature. Cementitious material leads to asymmetric flow. Learn more about Fly Ash Silos. Maintenance Schedules It’s essential to have a proactive silo maintenance schedule, ensuring continued, safe operation. While professional inspections are recommended every two to five years, unless there are structural or operational concerns that would necessitate more frequent inspections, frequent in-house inspections will verify that preventive maintenance measures are being followed. Silo maintenance should include regular checks of airflow units, a routine professional cleaning, and regular, complete silo emptying. Of these measures, one of the most important is the regular emptying of silos. Silos that are regularly emptied and refilled are less likely to experience buildup issues seen in those kept topped off. Regularly emptied silos need professional cleaning less frequently in comparison. They are also less likely to experience issues like compacting and hydrating. Hydration occurs when moisture mixes with stored materials and causes them to solidify within the silo. When this happens, materials can expand and cause added wall pressure which increases the likelihood of structural failure. The routine examination of your silo is only effective in increasing facility safety and ensuring smooth operations when it is conducted in conjunction with professional inspections (and cleaning services) as part of a regular preventive maintenance schedule. A recent case study provides an example of how asymmetric flow can cause silo failure. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on
Do You Have Cracks in Your Cement Slipform Silo Walls?
Prevention is the most effective method to ensure the integrity of concrete structures, surfaces and silos. A proactive maintenance and inspection program is crucial to increase the life of your concrete and ensure the safety of those working around your structures. A proactive safety program should always include annual or semi-annual inspections to check for concealed damage and to assess visible problems that could lead to structural failure. Though concrete is a superior material for the construction of storage silos, normal loading and unloading operations can lead to structural issues over time. Cracks in silo walls, linings and foundations are an indication of stress. Concrete walls that show horizontal, vertical or diagonal cracking may be an indication of delamination, or separation of the concrete into layers. Delamination of the concrete is caused by the lack of bonding to the interior structural steel reinforcement, thus weakening the silo’s structural capacity. Issues of this nature will require repair sooner rather than later. Delamination of silo walls can lead to wall failure or collapse and should be addressed by a professional silo repair company immediately. Corrosion of metal silo components, exposed rebar or other deterioration like spalling should also be noted during a visual inspection. Horizontal and vertical cracks are typically caused by temperature variations, moisture and internal pressure from the stored material. Cracks can cause concrete and steel rebar corrosion which can decrease wall stiffness, allow deflection, degrade durability and strength due to carbonation, and permit water penetration into the concrete wall. To repair cracks in a poured in place silo, an epoxy injection is used to fill in the cracks. After epoxy injection, it is recommended to add post-tensioned strands completely around the silo area of delamination to provide additional structural integrity. These strands can replace all of the original steel reinforcing and, assuming the concrete is still sound, the silo can be returned to its original load capacity in an economical manner. Much of this damage is preventable through routine inspection and maintenance. Third-party inspections, maintenance and repair services are the best way to manage safety on any scale. Many structural issues can be easily and economically addressed if caught early. One of our recent case studies inspects a slipform concrete silo with a horizontal crack. To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on