Pipelines are laid for more than a dozen years. Their repair, replacement of individual sections is an energy-intensive and costly undertaking. Pipe manufacturers are improving methods of protecting pipes from the action of aggressive environmental factors. A new word is reinforced and very reinforced pipe insulation based on extruded polyethylene. It increases not only the period of trouble-free service, but the mechanical strength of pipe products.
What is meant by VUS and US
Any type of insulation is understood as a multilayer structure of a coating of protective materials.
US — reinforced insulation is used in soils with resistivity from 10 to 20 Ohm * m.
VUS insulation has a decoding — very reinforced, it is necessary where the soil resistivity is less than 10 Ohm * m, which is typical for an increased corrosivity of the environment.
The main difference between these types of insulation is the thickness of the insulating layer.
Types of protective coating
The protective coating is divided into four types:
- Polyurethane foam. Pipes with insulation of this type form the basis of heating mains. They are designed to transport liquids with temperatures up to 140 0С, as they have thermal conductivity up to 33 mW/m0C and withstand a pressure of not more than 1.5 MPa. Protection is created by forming a shell of polyethylene galvanized coating. Service life up to 30 years. It is applied to ordinary and galvanized steel. Are made in accordance with GOST 30732-2006.
- Foam polymer mineral. It is used for insulation of heating mains with a coolant temperature of up to 150 0C and working pressure 2.5 MPa. Three-layer protection: anti-corrosion material, porous heat insulator, waterproofing. The thickness of the insulation can be increased due to the heat-insulating material and depends on the region where the heating main is laid. The waterproofing material can also serve as protection against impact damage. Pipes are produced according to GOST 17177-94 and TU577768-001-70440350.
- Rubber-bitumen mastic. Such protection does not improve the technical characteristics of the pipes, but increases the resistance to corrosion and is a waterproofing. According to GOST 51164-98, the base of the pipe is primed, mastic is applied, covered with a reinforcing non-woven fabric and an outer wrap. Waterproofing, mechanical protection indicators can be increased by applying several layers of mastic. Such pipes are not used for heating mains: at temperatures below -100C and above + 400With isolation is destroyed. The VSL with this method of protection is achieved by the number of coating layers.
- extruded polyethylene. An effective way to insulate pipelines with a working mixture temperature of not more than 800C. Increases the service life of pipes up to 50 years, enhances resistance to mechanical stress. Refers to a very enhanced protection. The quality of the pipe in VUS insulation and the process of applying insulation is regulated by GOST 9.602-2005.
In addition, steel cases can be used for increased protection against mechanical impact, for example, in those places where pipes are laid under a highway.
Advantages and scope of VUS
The advantages of using pipes with VUS relate to improving their operational and technical characteristics:
- guaranteed trouble-free use of the pipeline for more than 40 years;
- a high level of waterproofing allows you to lay pipes under water or in heavily flooded places;
- a wide range of operating temperatures from 500From to — 600FROM;
- energy-saving effect up to 30% due to an increase in thermal insulation properties;
- full protection against all types of corrosion, biological pollution.
If we consider the coating of extruded polyethylene as VUS, we can talk about the advantages of the insulating layer itself /:
- increased adhesion to metal;
- resistance to mechanical damage;
- low level of water absorption;
- dielectricity. Guarantees high contact resistance;
- environmentally friendly material that does not harm the environment.
The disadvantages include:
- high cost;
- the need for additional reinforcing insulation in regions with consistently low temperatures;
- impossibility to use for transportation of high-temperature environments
- limitation on working pressure 5.5 MPa.
Taking into account the pros and cons of pipes and fittings with insulated pipelines, it is recommended to use them in the following areas:
- all types of oil pipelines;
- industrial and domestic water supply and sanitation;
- pipelines for various purposes passing through an aggressive environment (any water bodies, including industrial waste, landfills, industrial waste);
- engineering gas distribution communications with a load of up to 2.5 MPa;
- places of laying with increased external influence.
How polyethylene insulated pipes are produced
The whole process is mechanized. It consists of several stages:
- Surface preparation. At this stage, the heated pipe passes through the shot blaster and is cleaned of rust. In this case, the shot creates a rough surface. The stage of dedusting and purification from the remnants of shot passes.
- Surface preparation control. Cleanliness is checked using adhesive tape and a reference sample, roughness is checked with a special device. These indicators determine the level of adhesion.
- Application of an anti-corrosion layer. The pipeline is heated with gas, the chromium alloy is removed from it, and the temperature is raised to 200 by induction heating. 0C. In this state, the epoxy primer is applied. Primer layer thickness up to 0.08 mm.
- Application of adhesive material. A thermofusible polymer composite with a thickness of at least 0.3 mm is used as an adhesive.
- Formation of a protective layer. The pipe is insulated with polyethylene-based materials. A tape base may be used.
After that, the product is cooled and dried. Next, the pipes are prepared for operation: up to 15 cm of insulation is removed from their ends and a chamfer is formed.
Production of pipes with bitumen-mastic insulation
Preparation for applying protection does not differ from polyethylene. But the superimposed layers themselves have a different composition:
- 1st layer of bituminous mastic;
- 1st reinforcing layer;
- 2nd layer of bituminous mastic;
- 2nd reinforcing layer;
- outer covering or layer wrap.
To achieve VUS, the number of reinforcing, mastic layers is increased, but this leads to an increase in the mass of the product. As bitumen-mastic materials, bitumen-rubber, polymer-bitumen films, other mastics from hydrophobic materials with various types of additives are used. For reinforcement, fiberglass or any non-woven fabric is used. The total thickness of the insulation can be up to 10 mm.
VUS pipes are manufactured industrially, their reliability is ensured by the requirements of GOST and is confirmed by a certificate. They comply with all modern standards that apply to pipelines operating in adverse external conditions.