The oil and gas industry is often considered an integral industry to the foundation of a country. Oil and gas production contributes significantly to a country’s budgets, its imports and exports, its income, and has a global effect on the value of its currency. Gas and fuel, derivatives of the oil refining process, power thousands of pieces of equipment, cars, and power plants. Moving, or pumping, fuel from one point to another is therefore integral to the successful operation of the entire plant or factory. Although gas and fuel are generally pumped through steel pipelines, there are instances when fixed structures are not an adequate conduit. When a flexible, mobile solution is required, or steel pipelines are not feasible, hoses and associated accessories take the stage.
By Jurij Artiukhov, General Manager, PipeTime, LLC
Hoses are used in almost every facet of the oil and gas industry. From the process of extracting oil from the bowels of the earth, to delivering the necessary fuel for the equipment at an oil refinery, hoses are used to pump water, oil products, air, and other liquids, including fuel.
Materials of Construction
As many types of fuel, such as diesel or gasoline, are quite aggressive in nature, the construct and materials of construction for a conduit hose must meet certain standards. The inner surface of the hose, in particular, must be made of a special material that is not only oil and petrol resistant, but also capable of withstanding the effects of fuel, high temperatures, and any chemical impurities that may be in the media.
Typically, the inner surface of the rubber fuel transfer hose is made of oil and petrol resistant NBR material. NBR (nitrile butadiene rubber or nitrile rubber) is a synthetic polymer material that is mostly used as the inner layer of rubber hoses for pumping fuel; its main property is high resistance to gasoline, diesel, etc.
The working temperature of the inner layer of the hose varies considerably. For example, in the territory of Russia and the Commonwealth of Independent States (CIS), there are special state standards that regulate the manufacturing of fuel hoses to meet a specific operating temperature. Typically, this standard is set at + 90˚C. If, however, one considers European or American counterparts, their use of special polymer additives in NBR material, change the allowable operating temperature to + 100˚C. Due diligence is therefore required by operators to ensure that the inner tube specifications meet the requirements of the task at hand.
If a fuel has additional chemical elements present, such as aromatic hydrocarbons or benzenes, then a NBR material is not suitable, as it will not withstand the corrosive nature of the media. To pump this type of fuel, ultra-high molecular weight polyethylene (UHMWPE) is used as an inner rubber layer. The temperature range of this type of polyethylene is + 80˚C to + 100˚C. UHMWPE is also recognized for its resistance to 98% of the chemicals used in industry.
Inner Tube Properties
Rubber hoses for pumping fuel are often subdivided into two categories: suction and suction-discharge. Depending on the intended use of the hose, the inner layer can therefore be reinforced with either textile polyester fiber, for suction pipes, or a combination of textile fibers and reinforcing steel wire, for suction-discharge hoses.
When conductivity is a concern, a copper wire can be woven into the inner layer along the entire length of the hose; in other cases, antistatic rubber can be used.
While there are many hoses that can be employed to transfer fuel, one of the most commonly used hoses for this application, especially in Russia, are ‘Durite’ hoses. ‘Durite’ hoses, named after the Latin word ‘Durus’, meaning ‘strong’ or ‘durable’, have a multilayer base, and are composed of a textile reinforced layer that can contain up to six layers of polyester winding. Each of the layers of the hose have mineral inclusions up to 3mm and it can maintain its internal cross-section during multiple bends or twists. It is therefore suitable for pumping gaseous media.
Hoses for Aviation Fuel
Rubber hoses that are used for refueling aircraft, differ slightly from the types used in other applications. In aviation fuel (kerosene), the percentage of aromatic hydrocarbons can be up to 50%, which is a serious challenge to the durability of the inner layer of the hose. In aviation hoses, the inner layer is therefore manufactured out of ETER: a thermopolymer rubber that is resistant to the aggressive effects of aviation kerosene, withstands temperatures up to + 100C and maintains its flexibility and elasticity at low temperatures.
The outer layer of rubber hoses for pumping fuel can be made of NBR, EPDM, and CR materials. Unlike the inner layer, the outer layer must be resistant to abrasion, weather conditions, have non-flammable properties, have an absence of copper strands inside the hose, and it must be antistatic. The best material to use to meet all these requirements is chloroprene rubber (CR); it is the most resistant to weathering and aging.
Rubber hoses for fuel, in most cases, range in diameter from 1/8″ to 8″. The working pressure depends on the diameter of the hose, but one can confidently say that the main pressures are 10 and 16 bar. If discussing high-pressure hoses, then the working pressure can increase to (50, 100, 400 bar). Higher pressures can be accommodated through the use of a steel frame in the inner layer of the hose.
The production process of rubber hoses allows them to be produced in coils that range from 10m to 120m. This size is dependent on the diameter, as well as with pressure; the larger the diameter, the smaller the hose coil.
Rubber fuel hoses are used throughout the oil and gas industry. One of their primary applications is to be used as temporary pipelines for supplying fuel to hard-to-reach places, such as fuel trucks, fuel hoses, etc. In the shipping industry, rubber hoses are also used to pump fuel (diesel, fuel oil) from ship to ship, or from ship to shore (bunkering operations).
As the oil and gas industry’s development is constantly progressing, rubber hoses are not always able to accomplish the assigned tasks for pumping fuel. Due to weight of rubber and difficulties with storage, logistics, operation, low operating pressure, and length limitations, the use of composite hose is often a viable alternate.
Composite hoses are available in a range of diameters spanning from 1″ to 12”, have a working pressure up to 10 bar, and are actively used for loading and unloading fuel and combustible materials from road, railway tanks, and tanks. To ensure that the hose is lightweight the outer layer is made of a durable PVC, and is reinforced with an aluminum spiral. To further protect against abrasion the outer layer is also represented by aluminum wire (or sometimes galvanized steel).
Bunkering hoses are resistant to seawater not only on the deck of a ship, but also in the open sea. Some manufacturers have developed a special series of rubber hoses for bunkering, which, when rolled onto a reel, become flat; the primary benefit of this is to save space on the vessel. Due to its low weight, great flexibility, and lengths of coil that can reach 30m, composite hoses are in great demand for bunkering operations.
Unlike rubber hoses, connecting elements for composite hoses cannot be installed manually. Composite hose requires the presence of special equipment, which is not always possible in the open sea or the remoteness of the production site from the repair shop.
Perhaps the most modern hose solution, for pumping fuel, are flat-rolled polyurethane hoses. Polyurethane hoses are made of thermoplastic polyurethane (TPU), which have improved oil and petrol resistance properties. The reinforcing frame is made of polyester that has been pressed with polyurethane during the extrusion process; this allows the hose to work with high pressures. TPU material is used both for the manufacture of the inner and outer layers of these hoses, because in addition to resistance to fuel, TPU is highly resistant to weathering, abrasion, and bending.
If necessary, polyester can be replaced with poly-aramid thread (Kevlar), and copper wire can be woven into the inner layer, which increases the strength characteristics of the polyurethane and relieves static stress, respectively.
Hose diameters range from 1″ to 16″ while the working pressure typically span from 10.16 to 40 bar. The working pressure is directly proportional to the hose diameter.
The extrusion process itself, in contrast to the mandrel process used in the production of rubber hoses, allows the production of hoses without limitation in length in the coil. For ease of use, segments from 100m to 200m, less often 500m, are common and can be cut to the desired lengths in the field.
One disadvantage to the polyurethane hose is that it is more susceptible to damage and it has a smaller bend radius.
Taking into account the aggressiveness of different types of fuel, the connecting elements for fuel hoses are made of stainless steel to ensure the proper corrosion resistance of the fitting. Connecting elements can be represented by Camlock, Storz, or flange connections.
Choosing one fitting over another depends solely on the production task, the requirements for the laying speed, and the resistance of the connection to high pressure.
The choice of a hose strictly depends not only on its intended application (in our case, it is pumping fuel), but also on operating conditions, climatic conditions, ease of installation, availability of storage space, and other factors. It is impossible to say unequivocally that one hose is better than the other, or that only a certain type of hose should be used; each type has its own advantages and disadvantages, and the choice always remains with the end user.