Considerations in choosing spouting

by Fred Fairchild
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Editor’s note: This is the second part of a series of articles about understanding the choices available when building new, expanding or replacing facilities and equipment. The first article appeared in the August 2015 issue of World Grain and more articles on this topic will appear in future issues of the magazine. This article will cover spouting types and sizes.

Every grain handling or processing facility uses spouting at many locations to carry product from one point to another. This can be a simple short connection between two pieces of equipment to long spouts connecting distributors to various bins and rail or truck loading points. This spouting can be round, square or rectangular, made with various wall thicknesses and other accessories such as liners or removable tops or bottoms.

Round Spouting

The most commonly used spouting is round steel tubes or pipe. Tubular spouting is made from sheet metal that is rolled into a tube with a welded lengthwise seam. It is available in wall thicknesses of 14ga.-7ga. Round tubing is measured by its inside diameter. The outside diameter is determined by the thickness of metal used. It is available in steel, galvanized and stainless steel metal.

For thicker walled spouting, structural piping is used. Piping wall thicknesses are available from 3/16-inch to 1/2-inch or greater. The inside diameter of pipe spouting varies by the wall thickness as the outside diameter is constant for a given pipe size. As an example, 10-inch pipe spouting is 10-3/4-inch outside diameter regardless of the wall thickness. A 10-inch pipe spouting with 1/4-inch wall thickness would be 10-1/4-inch inside diameter.

Comparative costs for 10-inch diameter tubular and pipe spouting are shown in Table 1 (Courtesy Nolin Milling, Inc.).

Round spouting is available standard in 10-foot, 20-foot and 40-foot lengths. Factory prime painted steel spouting will be an additional $1.50 to $2 per linear foot.

Square and Rectangular Spouting

Square and rectangular spouting is formed using sheet metal or metal plate, depending on the wall thickness chosen. Styles vary from fully welded construction to construction with removable tops and or bottoms. It is built in 10-foot sections with either plain or flanged ends. Removable tops allow access to the spout interior. This is especially needed if the spouting has any kind of a liner. Comparative costs for 10-inch square unlined spouting are shown in Table 2 (courtesy Nolin Milling, Inc.).

Spout Liners

Metal spouting will wear on the interior due to the type and amount of product it carries and the velocity at which it moves. If the metal in the spouting wears thin, it will be necessary to replace the whole spout. This can be avoided if a removable liner is placed inside the spouting that provides a better, longer-wearing surface that can be replaced without having to replace the metal spout itself.

Abrasive resistant (AR) steel liners provide a harder metal surface and can be used to line the inside of spouts. Other types of spouting liners are various grades of urethane sheets, ultra-high molecular weight (UHMW) sheets, ceramic chip imbedded sheets and ceramic tiles to use based on the severity of wear. These liners are usually manufactured in sheets with expanded metal backing to keep the liners rigid when installed. Replaceable liners can take the wear and then be replaced without affecting the body of the spout. Be careful when adding liners to spout interiors as they reduce the cross-sectional area of the spout and may reduce the capacity of the product flowing through the spout.

Sleeve liners for round spouting are available and normally made of urethane. One brand of round spout liner is called Tuff-Tube, a patented urethane spout liner manufactured by Sioux Rubber & Urethane. It is actually a urethane tube that fits inside the metal spouting. Other sources use metal backed urethane rolled into tubes as a liner.

For square or rectangular spouting, sheet liners are used. One choice is to use an (AR) steel liner in the bottom and sides of the spout. It is also used in locations where material is irregularly shaped and would gouge other liner materials. UHMW is a hard surfaced material that is a vailable in many thicknesses.

Metal backed urethane may also be used as a liner in areas where the wear is due to friction of the product on the surface. Urethane is not good for impact resistance or for handling materials that would gouge the surface. Ceramic chip and ceramic tile liners are used in the highest wear cases and may last as much as 15 times longer than the original spout material. Ceramic liners are expensive for initial purchase, but may be quite inexpensive over the life of the liner. Table 3 shows comparative costs for various types of liners (courtesy of Nolan Milling, Inc).

Choosing the Best Spout

With all of the possibilities discussed above, selecting the correct spout for an application is important. The following should be considered in the selection:

1) Material to be handled through the spout
    a. Density
    b. Moisture content
    c. Abrasiveness
    d. Flow characteristics
2. Required flow rate
3. Exterior exposure of spouting
4. Capacity of spout (net area inside)
5. Length of spout
6. Service life of spout
7. Need for a liner
8. Dead box at end

For most low volume spouting handling mild or slightly abrasive materials, the suggested wall thickness should be 10-gauge steel tubing with a painted or galvanized exterior. For more severe products or greater volumes, the wall thickness should be increased or a liner used in the spout to preserve the useful life of the spouting. This is a place where thicker walled steel pipe may be used instead of metal tubing. Round spouting can be rotated 180 degrees if wear starts to occur on the material flow contact area of the surface. This rotation will double the life of the spout without having to replace it.
Spouts over 40 feet in length should be supported by an exterior truss system to minimize deflection of the spout due to spout and operating loads or windy conditions. At the end of the spout should be an elbow or dead box to slow the velocity of the material and direct it vertically into the bins or equipment it is delivering material to.

For high volume spots or spouts handling abrasive materials such as whole soybeans or minerals, square or rectangular spouting with interior liners and a removable cover would be a better choice.

For severely abrasive product at high flow rates, ceramic chip or tile liners would be the best choice. Ceramic liners will last almost indefinitely if installed properly. Contact the liner supplier for the best choice of liner for your material and installation. Recommended minimum spout slopes are: dry grain – 40 degrees; wet grain or pelleted product – 45 degrees; soft ingredients or sluggish materials – 50 degrees or steeper.

Spout Sizing

The net spout cross-section area inside determines the approximate capacity that may flow through the spout. Suggested maximum flow rates through the spout are 70 bushels per hour per square inch of net interior area for whole grains and free flowing materials. For soft or sluggish flowing ingredients, the maximum flow rate should be reduced by 20% (this is a rate of 70 cubic feet per hour per square inch of area).

An example of safely sizing a spout for handling 8,000 bph of grain would be as follows: Q = V x A. Q = 8,000 bph. V= 70 bph/inch square. A = Q/V. A = 8,000 bph/70 bph/square inch = 114 square inches.

Minimum interior dimensions required would be: round = 12-inch diameter, square = 11-inch x 11-inch.

These same spouts would carry approximately 8,000 cubic feet per hour and 8,400 cubic feet per hour. 1 bushel is equivalent to 1.25 cubic feet.

These are suggestions for choosing the correct type and size of spouting required. The final type and size should be reviewed and confirmed with the spouting supplier or an engineer.

Fred Fairchild is feed science professor emeritus in the Department of Grain Science at Kansas State University. Prior to coming to Kansas State in 1994, he worked in the industry designing, constructing and commissioning numerous mill facilities. He is a licensed professional engineer. He can be reached by e-mail at