Proper Steam Hose Selection Leads To Performance, Safety, And Economic Benefits

There are powerful economic and safety reasons for properly specifying and handling steam hose assemblies.

02/01/1998


There are powerful economic and safety reasons for properly specifying and handling steam hose assemblies. Economically speaking, it is important to acknowledge that steam hose assemblies will fail prematurely if they are not properly selected and handled. Extreme pressures, temperatures, and stresses make eventual replacement inevitable. It makes strong economic sense to do everything possible to get the maximum life out of a steam hose assembly.

In safety terms, workers' lives are at stake. Steam hoses routinely carry pressures of at least 250 psi and temperatures up to 450 F, with short-term spikes that can go much higher. Improper specifications or handling procedures can cause an accident with catastrophic consequences.

Construction

Typical steam hose consists of three distinct parts: tube, reinforcement layer, and cover (Fig. 1).

Tube

The tube, on the inside of the hose, is designed to withstand high steam temperatures and resist any additives. It is normally manufactured from chlorobutyl or EPDM. Steam hose tubes cannot tolerate exposure to petroleum products or many other chemicals, which weaken the tube and cause early failures.

Steam hoses must only be used for steam. If a steam hose is used for anything else, it cannot be returned to steam service.

Reinforcement layer

The reinforcement layer around the tube provides external protection, resists high internal pressures, helps eliminate static charges, and ensures that fittings stay on the hose. Many reinforcements are made from a braided steel wire which resists high-temperature deterioration, while some fabrics, textiles, and stainless steel reinforcements lose their tensile strength. Don't use a hose designed for another fluid to transfer steam.

Many steam hoses have ground wires that help eliminate the static charges that build up inside the hose and are an important safety feature. Static charges are more likely to occur with larger hoses and during cold weather.

Cover

The cover of the hose is just as important as the tube and reinforcement. It is typically made of chlorobutyl or EPDM, and protects the hose from abrasion, chemicals, and environmental hazards; and helps prevent the reinforcement from rusting. Since oil is harmful to steam hoses, many manufacturers make oil-resistant covers available where the risk of oil contact is present.

Steam hose covers should be pin-pricked. This important safety feature allows the release of gasses which can build up between the layers in steam hose as it heats and cools.

Selection factors

There are many facts that have to be known about an application before a steam hose can be specified. Some of the most important considerations are:

- Steam pressure

- Steam temperature

- Whether the steam is superheated or saturated

- Magnitude of surges in temperature or pressure

- External conditions where the hose will be used

- How often the hose will be used

- Duration of each use

- How long the hose will be idle

- Whether manual handling will be required.

It is helpful to read the lay line on steam hose. Every hose designed for steam use should be marked with the manufacturer's name, hose type, and operating pressure. If this information is not visible on the lay line, don't use the hose for steam. Many steam hoses are also date-coded with the time of manufacture. This information helps spot hoses that should be replaced due to age.

While many industrial hoses have a built-in safety factor of 4:1 (they can withstand pressures four times greater than the rating on the cover), steam hoses have a minimum safety factor of 10:1, per standards of the Rubber Manufacturers Association. This factor emphasizes the extreme dangers present with steam use. A hose should never be used to carry pressures higher than it is rated to handle, in spite of the safety factor.

Hose couplings are extremely important when steam is being handled. The potential for serious injury is significant if a coupling blows off under pressure. High temperatures and pressures inside steam hose act like a pressure cooker and cause the inside and outside diameters to shrink during use. Couplings must be specifically designed to combat this effect (Fig. 2). Only couplings designed for steam hose should be used, because they include several crucial features:

- Proper material for steam, usually plated steel

- Bolt-on clamp which can be retorqued repeatedly

- Ground-joint connection to avoid static charge buildup

- Strength to resist slippage due to hose shrinkage.

Maintenance and storage

The life of steam hose can be significantly lengthened with proper care between uses. The safety of workers is also enhanced.

Steam hose should be completely drained after use and before hanging. Storage should take place at normal temperatures, not hot or cold extremes.

Sharp bends in the hose must be avoided. Racks should not permit bends sharper than the hose's rated minimum bend radius. Weight of steam hose can cause kinks that other hoses might not experience, and kinks or sharp bends can damage the steel reinforcement.

Steam hose should be hung only from a rack specifically designed for it, never from an ordinary hook or nail. Whatever rack is used, it should be completely dry before the hose is placed on it, or cover damage can result.

Workers should make a habit of inspecting steam hose both before and after each use. They should look for any signs of possible damage, including cuts, cracks, kinks, flattened areas, blisters or lumps on the cover, and any exposed or frayed wires. All clamps, couplings, and other fittings should be inspected for steam damage.

It is good practice to start a regular program of having steam hoses inspected by trained distributors or fabricators at least every 180 days. If a steam hose is damaged or old, it should be replaced immediately.

-- Edited by Joseph L. Foszcz, Senior Editor, 847-390-2699, j.foszcz@cahners.com

Key concepts

Base selection on operating conditions

Never exceed the pressure rating

Only use couplings designed for steam service

Examine steam hose regularly; use qualified inspectors

14 recommendations for working with steam hose

1. Install an OSHA-approved safety cable on the hose at every junction to prevent whipping of the end if the coupling should disconnect.

2. Ensure continuous static grounding of the hose at each coupling.

3. If the clamps are a bolt-on style, tighten them to the correct torque before use. Use calibrated torque wrenches, not impact or other types.

4. Repairs on steam hoses and couplings should only be done by fully qualified distributors or fabricators.

5. All workers near the hose should wear full protective safety gear including gloves, safety shoes, full-length protective clothing, and protective glasses or goggles.

6. Perform a complete safety check before the steam is turned on. Inspect the area and remove all unnecessary objects and debris. Inspect the hose for gouges, kinks, worn areas, loose couplings, and other potential safety problems.

7. Install a shut-off valve between the source of steam and hose assembly.

8. Use spring guards to protect the hose from kinking when handling of the hose is required.

9. Avoid excessive flexing of the hose, particularly near couplings. Flexing can weaken the assembly.

10. Examine connections to the steam source. Use straight connections instead of bending the hose. Install pipe elbows to ensure either straight vertical connections pointing downward, or a 45-deg downward angle that allows the hose to gently contact the ground without too much flexing.

11. Be aware of the danger of hammer effect and take steps to prevent it. Hammer effect is caused by spikes of extreme pressure; it can damage hose assemblies and break couplings free. The usual causes are blockage, pinched-off flow, or valves being opened or closed too fast. Make personnel aware of both the danger and causes, and urge them to avoid actions that can cause the hammer effect.

12. When finished using steam, always close the pressure valve from the steam source. In addition to providing an extra safety margin, this action can extend the working life of the hose.

13. Add an extra measure of safety by ensuring that all steam hose connections are incompatible with other hoses in the plant or by color-coding for different applications. Manufacturers can often cooperate with these requests and suggest good color-coding systems.

14. Train workers to look for signs of problems during usage, such as steam leakage, loose clamps, hose shrinkage, cover damage, or exposed reinforcement.

More info

For more information concerning this topic, contact Boston Products at 800-251-1410 or visit their website at www.dana.com/boston





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