Steam Hoses - How They Work

Steam hose

Figure 1: Steam hose

Steam hoses are specialty rubber hoses designed to convey steam to and from various points in a process. These hoses are generally made from synthetic Ethylene Propylene Diene Terpolymer (EPDM) rubber due to its excellent resistance to heat, water, steam, acid and alkalis, ozone, and sunlight. In general, all steam hoses have a steel/high tensile strength material inlay except for special use low-pressure steam hoses. Steam hoses are classified into two types: low pressure and high pressure, and each type into two classes discussed below.

Table of contents

What is steam?

Steam is the gaseous state of water. Most mineral substances available on earth can exist in three physical states: solid, liquid, and gas. It is also referred to as the different phases of the substance. In the case of water (H2O), the terms ice, water, and steam are used to denote the three phases, respectively. The water molecules are packed close together in the solid-state, preventing them from changing shape. In the liquid state, H2O molecules move freely, breaking and forming a bond again. As water is heated, the molecules gain sufficient energy to break free from the hydrogen bonds that keep them together in water, and these ‘free’ molecules enter the gaseous phase as steam. Steam is used as a heat source for propulsion in various industrial processes.

Properties of steam

  • Steam is colorless, tasteless, and odorless.
  • It can carry large quantities of heat efficiently from one point to another.
  • Steam is produced from water, which is cheap and readily available in nature.
  • Steam can be used as a heating medium in industries.

Types of steam

There are three types of steam depending on the temperature and pressure: dry, wet, and superheated steam. The different forms of steam are used for various applications and require proper hose selection to ensure efficient steam transfer.

Dry steam

Dry steam, also known as saturated steam, refers to steam whose water molecules do not condensate (water vapor turning back into liquid water). Dry steam is formed when water is heated to its boiling point and then vaporized with the help of additional heat. Dry steam exhibits various properties, which makes it an excellent heat source. For example, rapid and even heat transfer improve the desired process's quality and productivity. It is also safe, clean, and low cost as it originates from water.

Wet steam

Wet, or unsaturated, steam refers to steam that has the presence of moisture in it. When water is heated to its boiling point and vaporized, some water molecules lose their latent heat energy and condense to form tiny water droplets. The mixture of water droplets with steam is called wet steam. Figure 2 shows the formation of wet steam.

Wet steam

Figure 2: Wet steam

Superheated steam

Superheated steam is obtained by heating dry (saturated) steam beyond its saturation point. At the same pressure, superheated steam can provide higher temperatures and lower density when compared to saturated steam. Superheated steam is mostly used in the power generation industry for the propulsion of turbines. In a superheated state, steam does not condensate inside the steam-driven equipment. This maintains the dryness of the equipment and reduces the risk of corrosion.

Types of steam hoses

ISO 6134 has classified steam hoses to convey saturated steam and hot water condensate into two types:

  1. Type 1: Low-pressure steam hose
    1. Corresponding temperature: 164°C
    2. Maximum working pressure: 6 bar
  2. Type 2: High-pressure steam hose
    1. Corresponding temperature: 210°C
    2. Maximum working pressure: 18 bar

These two types of hoses are further classified into hoses with an oil-resistant cover or non-oil resistant cover.

Oil resistant cover

Oil-resistant steam hoses suffer little or no degradation when exposed to oil. These hoses are typically designed to withstand high temperatures up to 207°C (406°F) for saturated steam and 232°C (450°F) for superheated steam. Figure 3 shows an example of an oil-resistant steam hose. Steam hoses with oil-resistant covers are used in chemical plants, refineries, and processing factories where there is a chance for the steam hose to be in contact with oil.

Oil-resistant cover steam hose

Figure 3: Oil-resistant cover steam hose

Non-oil resistant cover

Non-oil resistant steam hoses are designed for general applications like moisturization and heating (discussed later in the article). Typically, they have more service life than oil-resistant hoses but are prone to damage if exposed to oils or high temperatures, especially in industries exposed to hydrocarbons like diesel-based inverted muds, lubricants, and cleaners. Under such exposure, these non-oil resistant covers soften and swell, causing them to tear. As a result, the hose gets exposed to moisture, initiating corrosion and losing its ability to contain pressure.

Points of attention

Steam can be dangerous and costly to work with. However, it is also a vital driving force of many industrial processes, as discussed later. Therefore, special attention must be given when selecting, installing, and fitting steam hoses. The following points require attention to prevent damage and increase the life of a steam hose.

Superheated steam vulcanization

Due to the high temperature and dry nature, superheated steam may harden the inner surface of the rubber, known as vulcanization. Vulcanization reduces the service life of the rubber. The chart in Figure 4 shows saturated steam being transformed into superheated steam. A steam line at a pressure of 18 bar and 2100C contains saturated steam. If the pressure is reduced by the expansion of the steam, such as when the steam suddenly passes through a larger hose or the sudden opening of a steam valve, the steam condition follows the red line into the superheated area. This condition does not last for long, but the superheated steam tends to deteriorate the tube stock in an ordinary steam hose intended for use with saturated steam. This results in steam hose failure in the long run.

Temperature vs pressure range according to steam type

Figure 4: Temperature vs pressure range according to steam type

Popcorning

The inner layer of steam may absorb water or water vapor during use. Once the hose cools down, it condenses the steam into water trapped inside the rubber hose. When the hose is used subsequently, the trapped water expands considerably, creating air bubbles in the inner wall due to the increased volume. As a result, blisters are formed on the inner wall, blocking and contaminating the steam with rubber pieces. The damage thus caused is called popcorning.

One of the measures to prevent steam hoses from popcorning is to blow dry them after each use. But it is a time-consuming process and very rarely done, further increasing the risk. Steam hoses with extruded inner walls can also be used to avoid this problem in addition to draining. These extruded inner walls are made from gas-tight rubber and are seamless and homogeneous. So, the water vapor cannot penetrate the walls, thus preventing popcorning.

Rusting inlays

Steel inlays are fitted into steam hoses as a standard practice. Due to the porous inner wall in these rubber hoses, steam comes into contact with the steel inlays, leading to corrosion. Since the corrosion takes place beneath the surface, the damage may stay hidden, leading to dangerous consequences. The weakening and cracking create escape ways for the steam without any warning. In such a situation, if the pressure is increased to maintain a constant flow of steam, the risk of bursting a hose increases, which can be a dangerous situation.

To avoid such a situation, galvanized steel inlays are used. They are resistant to rust, thus increasing the safety and service life of the steam hose. Other advantages of galvanized steel inlays include reduction of the cost that may incur from steam loss which can be very high.

Rusting of steel inlays

Figure 6: Rusting of steel inlays

How to select a steam hose

Selecting a steam hose for your application requires careful consideration. The main selection criteria are:

  1. Dimensions: Determine the desired length and inside/outside diameter required for your application.
  2. Operating Range: The type of steam being working with (dry, wet, superheated) will determine the choice of steam hose.
  3. Temperature: Ensure that the steam hose can withstand the maximum temperature it is exposed to.
  4. Pressure: Ensure that the steam hose can withstand the maximum pressure and, if necessary additional pressure. Typically, a steam hose has a built-in factor of safety (usually 10:1), but this should not be considered when sizing a hose, and your factory's safety should be used. The maximum pressure of the hose shouldn’t be exceeded.
  5. Material: Ensure that the material is resistant to heat, water, and steam and does not react with the fluid or chemicals it is exposed to.
  6. Other working conditions of the hose: Always select a hose that matches its working conditions like:
    1. Frequency of use (whether the hose is used occasionally or continuously)
    2. whether the hose requires manual handling or not
    3. the configuration of the hose (whether bent or straight) while working under pressure
    4. External working conditions of the site where the hose works ( to check for the possibility of mechanical knockouts or spilled chemicals in the vicinity)

Common applications

Steam is used for various applications in a wide range of industries. According to the requirement, steam hoses are used to channel dry, wet, or superheated steam for these applications. Some of the common industrial applications are discussed below.

Hoses for heating

Food processing factories, refineries, and chemical plants use steam as their heat source. Steam hoses are used to allow flexibility and easy deployment of steam. Refineries use steam hoses to provide heat for lubricating and increasing flow for tank and vessel cleaning. Food processing factories channel high-temperature steam through steam hoses for sterilization purposes. Process fluid heat exchangers, reboilers, reactors, combustion air preheaters, and other heat transfer equipment use saturated (dry) steam as a heating source.

Steam turbine propulsion hoses

Steam turbines use steam as a driving force for propulsion applications. Steam turbines are used in thermal electric power plants to generate electricity. Steam hoses are used to move the steam from one place to another. This helps in the formation of energy through the movement of heat particles of the steam.

Steam turbines in a power plant

Figure 7: Steam turbines in a power plant

Hoses for cleaning

Steam cleaning is also a common application requiring steam transfer. One example includes steam cleaning with soot blowers. Soot/deposits, when stuck to the heating surface, act as insulators preventing the smooth transfer of heat. Soot blowers remove these deposits from the furnace walls. Boilers are generally equipped with soot blowers, which release steam through the nozzle, thus removing sintered ash and slag.

Hoses for moisturization

In some industries, steam is used when the process requires moisture and a heat supply at the same time. Some examples include the paper production industry and pellet mills. In the paper industry, moisture is supplied to paper moving over rolls so that they do not suffer microscopic wear and tear, and at the same time it improves sheet strength. In the production of pellet mills, steam is used to dry and provide water content to the feed materials.

Hoses for humidification

Many facilities use low-pressure saturated steam as their primary source for indoor heating. This is especially common in cold climate regions. Steam hoses are used for steam transfer purposes in such settings. When cold air is heated by HVAC coils, the air humidity drops. So, it is often combined with steam humidifiers that inject dry saturated steam, conditioning the airflow, thus providing indoor comfort, preservation of books and records, and infection control.

Steam atomization

Steam atomization is the process of mechanically separating fluid using steam. This process is mainly used in oil burners to maximize combustion efficiency and minimize soot production. When the steam is injected through a steam hose, the oil breaks up to form small droplets which mix with air allowing for efficient combustion.

Steam as a motive fluid

Steam is used as a motive fluid to force the movement of other fluids in piping. High-pressure motive steam passes through the nozzle to the jet ejector, which is then diffused. This results in an increase in velocity and a decrease in pressure. The high-velocity motive fluid combines with air from the surface condenser, thus flowing at an intermediate pressure. This process is used on distillation towers to separate and purify process vapor streams.


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