Mine slurry hoses

By |  March 5, 2015

Selection and usage recommendations for longer-lasting and better-performing hose assemblies.

Many design engineers and maintenance managers believe that a hose assembly is nothing more than a fixed asset – a permanent feature of an operation. Yet, when a mine slurry hose does reach its inevitable end of life, maintenance teams are often caught off guard, and must quickly find a matching or suitable replacement.

The cost of a new hose may be nominal in the overall maintenance and operational budget. But shutting down a line immediately to replace a hose may disrupt operations and significantly impact productivity. With better initial hose specification and a better forecast method for replacing hoses, the operation’s productivity will improve.

Many factors must be considered when selecting the correct components for a hose.

Hose assembly selection factors

The best way to remember the factors that are important in hose and assembly selection is to use the acronym STAMPED, which stands for:
S – Size. Inside diameter, outside diameter and overall length
T – Temperature. Internal and external
A – Application. Flexed, static and usage
M – Material. Material being conveyed
P – Pressure. Working pressure, vacuum
E – Ends. Type and fixed
D – Delivery. How quickly is it needed?

Most mine slurry hose assemblies are specified by their inside diameter measurement. In many highly abrasive systems, where pipes and other wear components are lined, the hose specifier should be aware that the inside diameter of the hose may need to be adjusted to meet this specific type of system requirement.

In addition, pipes that are greater than a 12-in. inside diameter are measured by their outside diameter. So an operation that is ordering a larger bore hose to match such a specific pipe system also needs to know the pipe’s outside diameter, schedule (thickness) and whether the system is lined.
For example, let us suppose an operation needs a replacement hose in a 16-in. pipe system. The pipe is standard schedule (40) thickness with a 1/2-in. rubber lining.

To calculate the correct hose of a 16-in. pipe:
■ 16-in. outside diameter
■ Schedule (40) thickness
■ 15.25-in. unlined inside diameter
■ 14.25-in. lined inside diameter

This operation would need to specify a 14.25-in. ID hose for optimal fit and function within this system.

Temperature can have a major effect on hose selection. This applies not only to the material being conveyed, but also to the environmental temperature surrounding the exterior of a hose.

To the first point, temperature of material being conveyed may affect the tube rubber in a hose. For example, a chemical being conveyed at an ambient temperature reacts differently with the tube than chemical being conveyed above 100 degrees.

Exterior temperature also impacts hose material composition selection, so knowledge of both temperatures is necessary to provide the longest life possible.

Application considerations

How will the hose be used? Will it be static like a pipeline, or will it be flexing regularly, as a dredge hose might? Application conditions tell a hose engineer what kind of materials should be specified to provide the best hose construction for the particular conditions.

The material being transported is a key determinant in selecting the most suitable tube for a hose. A hose that is conveying highly abrasive coarse aggregate slurry requires a different tube material than one for very fine aggregate slurry. A dry material also requires a tube with a higher durometer rating to defend against the high rate of wear that these types of materials often generate.

Specific gravity, velocity, particle size, moisture content and chemical composition are among several factors that provide a hose engineer the necessary information for selecting the best tube material for optimum life.

Pressure ratings

Hose working pressure is generally rated in pounds per square inch (PSI). An operation should know the working pressure of the system, as well as any potential pressure spikes the system could be susceptible to. Hoses should be manufactured and tested to withstand maximum surge pressure. In other words, compensation for pressure surges, spikes or jumps should be taken into consideration and should not exceed a hose’s maximum working pressure. Failure to select a hose that meets this criterion could lead to end blow-offs, hose leakage and hose bursts.

Hose assemblies are usually built with a safety factor of 3-to-1 or 4-to-1, based on working pressure and/or industry standards. Hose manufacturers should periodically pressure test hose assemblies to one-and-a-half times their working pressure during the manufacturing process to ensure they are maintaining quality construction compliance.

In addition, vacuum conditions should also be reviewed. If a hose cannot pull the correct vacuum, performance will decrease and potentially lead to damage of both the pump and the system.

 

Ends: flanges, fittings, clamps and couplings

Selecting the correct ends for a mine slurry hose assembly goes far beyond the desire for ease of installation. All of the factors discussed above should be taken into consideration in order to select the best end for each hose assembly.

All flanges are designated to a particular class based on the flange’s composition, such as cast iron or steel, and the type of threaded material used for the fittings. Based on the class ratings, there are several characteristics, such as pressure-temperature ratings, bolt and nut dimensions, coating materials and other factors that create the standards.

For most mining and material handling applications, hose assemblies use an ANSI (American National Standards Institute) class flange. The table above shows typical ANSI class flanges and their ratings for mining and material handling. Note: There often is confusion that an ANSI class 150# flange is rated to 150 PSI. This is not the case. Based on B16.5 carbon steel, an ANSI class 150# flange may be used on a hose assembly rated up to 290 PSI.

Camlocks and King Combination fittings are also commonly used as hose assembly ends. Unless clearly verified by the assembly manufacturer, band and/or bolt clamps should only be used in low-pressure applications where material contamination is not an issue.

Built-in steel nipples may provide a secure coupling, especially if there is tugging, twisting, pulling or bending that may occur at the end of the hose.
Although it is not a design consideration, per se, understanding when a hose will reach the end of its life and a new hose must be available for installation can be a key consideration and is of critical value.

Installing a wear indicator system may slightly increase the initial cost of a hose, but is a highly proactive way to identify when a hose has reached a low percentage of life expectancy. Knowing this can significantly reduce the chance that a line needs shut down immediately, disrupting operations and impacting productivity and profitability.

RFID technology can be installed within a hose to provide monitoring of both wear life and maintenance needs – ultimately providing improved forecasting for hose replacement.

Normal hose life

Elastomeric hose and hose assemblies are generally controlled by SAE AS1933. This standard establishes age limits for acceptance of hose and hose assemblies that contain elastomeric materials for use in aircraft, space vehicles, missiles and component assemblies. This standard states that the hose or hose assembly shall not be greater than 32 quarters (eight years) old at acceptance by a government agency or ultimate user/customer. Per SAE AS1933, the elastomeric hose/assemblies must be stored under ARMA (Adaptability Rating for Military Aviation) conditions.

Shelf or storage life is the period of time from cure date to the limit that the rubber hose or hose assembly may be stored under proper conditions, and still retain a reasonable expected service life. Protection from undue aging during shelf storage as outlined by the ARMA should be followed. This includes avoiding storage in excessive heat and/or cold, sunlight and exposure to ozone.

If ARMA procedures are followed, the hose/hose assemblies should be inspected for their current condition at the prescribed shelf life limit. At that point, storage life may be, and often can be, extended.

Service life is measured from the point of installation, and only the user/manufacturer can establish this period. Service life also is greatly dependent upon the application. For example, take two identical hose assemblies: One operates at 70 to 100 degrees ambient and fluid temperature and with relatively steady pressure. This one will greatly outlast another hose assembly operating at 225 degrees and under irregular pressure service.

Factors affecting hose life

There are numerous unique factors and variables that can affect hose life. The main factors to consider include hose handling, type of material being conveyed, material pressure, material temperature, type of tube rubber and ambient conditions.

Unfortunately, there are only a few signs that indicate that a hose is nearing the end of its service life. One such sign is if material is leaking from the gasket area where the hose is connected. Another is material leaking through the outside cover of the hose itself.

In order to limit these failures, always start with the correct hose construction for the intended application and ensure that it is installed without damage and handled properly.

Jeffrey Potter is hose product manager for Weir Minerals, www.weirminerals.com.

This article is tagged with and posted in Features
Allison Kral

About the Author:

Allison Kral is the former senior digital media manager for North Coast Media (NCM). She completed her undergraduate degree at Ohio University where she received a Bachelor of Science in magazine journalism from the E.W. Scripps School of Journalism. She works across a number of digital platforms, which include creating e-newsletters, writing articles and posting across social media sites. She also creates content for NCM's Portable Plants magazine, GPS World magazine and Geospatial Solutions. Her understanding of the ever-changing digital media world allows her to quickly grasp what a target audience desires and create content that is appealing and relevant for any client across any platform.

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