Steel pipelines are used for transportation of natural gas, crude oil, petrochemicals, and water at high pressure over long distances. In order to protect the pipes from corrosion, external coating and cathodic protection are used.
There are 5 common types of steel pipeline protection which are chosen depending on different environmental elements, costs and standards:
1.Three layer high density polyethylene (HDPE) for operating temperatures from -45⁰C to +90⁰C
2.Three layer polypropylene (PP) for operating temperatures up to +110⁰C
3.Fusion Bonded Epoxy (FBE)
4.Coal tar, asphalt enamel
5.Polyurethane (PUR)
Polyethylene-based systems offer excellent mechanical protection and long-term aging performance. The three layer high density PE is the most commonly used protection worldwide
A Three layer System consists of an epoxy primer and an adhesive to bond the epoxy primer with a polyolefin topcoat. Polyolefin-based systems offer excellent mechanical protection and long-term ageing performance.
We provide the top two layers (adhesive and HDPE) of the 3-layer steel pipe coating system.
The top coat products fulfil the requirements in domestic IGS-C-TP-10, IPS-G-TP-335 and international ISO 21809-1, NF A 49710, DIN 30670, CAN/CSAZ245.21 and prEN 10285 standards.
We are ready to supply HDPE satisfying any of the above standards per our customer’s needs.
Three layer polyethylene coating
Introduction:
Three Layer Polyethylene Coating is a kind of highly resistant, durable, and efficient coating which is used for various pipeline transferring oil, gas, water and other liquids.
Three layer polyethylene coating, is highly adhesive and tightly adheres to the steel pipes and protects them in several aspects. Although, it can be removed easily by making use of heat when it is necessary. Three layer polyethylene coating is also very resistant to various kind of chemicals. This property allows you to use coated pipelines in any sever condition and in all kind of soils. As this coating is chemical resistant, it is resistant to corrosion as well, and so it is very durable.
When steel pipes are coated with three layer polyethylene coating, they acquire the properties of plastic and their durability and resistance increases significantly and can perform efficiently underground for a very long time.
The best choice for protection of pipelines buried underground is making use of three layer polyethylene coating.
Call our company to get access to the best material with efficient and professional service, in a timely manner. Several tests are down to ensure best quality of the final product.
You can trust our experience and professional experts.
The layers of polyethylene coating:
As it is clear by the name, this corrosion resistant coating is made of three compatible layers as they are briefly described below:
1. The first layer is an epoxy primer which is in the form of powder and it is sprayed with an electrostatic charge onto the heated pipe. The epoxy primer is a good adhesive which tightly adheres to the steel surface of the pipe as well as the second layer of the coating.
2. The second layer is a polyethylene copolymer which adheres to the epoxy primer from one side and to the third thicker polyethylene layer from the other side. This copolymer is a kind of adhesive which creates very strong bonding to both side layers. The copolymer adhesive should be compatible with the other two layers.
3. The third or the external layer is a thick layer of polyethylene which is resistant to all kind of chemicals as well as physical forces that may damage the pipeline. This top coat layer is a readymade compound which is black in color and it is completely stable against sun light (UV radiation), high temperature, and oxygen.
When these three layers are used together, they add to each other’s performance advantages and result in a final strong and durable coating with brilliant characteristics.
Various diameters of pipes (from 21.3 to 1220 mm) with different length ranging from 8 meters to 18 meters, can be coated by means of three layer polyethylene coating. Related services and adequate instructions will be given by our company.
Features and advantages of three layer polyethylene coating
• This durable coating is highly resistant to mechanical forces and damages, so while being transported and during installation phase, the coated pipes will be safe and no damage may occur.
• This three layer polyethylene coating is highly resistant to high temperatures, moisture, various chemicals and UV radiation and it can tolerate sever conditions for a long time.
• This coating has an excellent adhesion to the surface of steel pipes.
• It is excellent for buried pipeline and it provides maximum corrosion protective effect for so many years.
• This coating completely protects pipe welds.
• Coated pipes can easily connect to each other without causing any damage to the coating.
• Three layer polyethylene coating is not hazardous for nature and does not cause environment contamination.
Application:
The exact specification of temperature, application process and curing time are given by the producer company. Provided instructions of the company should be observed accurately and all stages of the process should be controlled and assessed qualitatively.
The process of application is briefly described below:
1. First of all the surface and inside of the pipes should be completely clear to gain a pure and smooth surface. All kind of contamination including oil, grease, dust, etc. should be removed prior to coating.
2. Then the pipes should be preheated.
3. After heating the pipes, epoxy powder will be sprayed to the heated pipes with special tools which impose electrostatic charge on the powder.
4. The other two layers will be applied over the epoxy layer within a predefined range of time and temperature.
5. At the end of the process, coated pipes will be cooled down by making use of water.
For application of three layer polyethylene coating, several preconditions should be observed. Also, special equipment and a proper plant are needed. In this regard, the general points are briefly given below:
General points:
• The person who is going to make use of three layer polyethylene coating (the applicator) should accurately know the requirements and instructions, and he should teach necessary points to the staff.
• The scale of the project should be evaluated and size of the plant should be proper for the project and time schedule should be defined. The work should be continuous and nonstop.
• The machinery, equipment and other required facilities should be in the best working condition and they should not be worn out in order to result in high quality coated pipes.
• Your plant should be equipped with a booth for epoxy spray, with suitable size for your project as well as a storage room for storing the coating materials and pipes. This room should be equipped to air conditioning facilities and its humidity and temperature should be regularly recorded. The Applicator should predict and provide necessary space and area for all of the materials and pipes (both bare pipes and coated pipes).
• During the coating project, a group of experts should be responsible for quality evaluation or quality assurance of the process and the products. The minimum thickness of the coating should be based on the instructions and the quality assessment group should read the coating thickness of coated pipes. Surface of the bare and coated pipes should be observed carefully by this group in order to detect any kind of defect or irregularity. Defected costings should be out aside by this group.
Coating process:
As it was mentioned before three layer polyethylene coating consists of three layers. The top coat or the surface layer, is a polyethylene with high density. The middle layer is an adhesive copolymer and the inner layer is an epoxy primer.
Epoxy primer is in the form of powder and its color can be dark red, green or other colors which are approved. The gray color is not approved.
The copolymer adhesive should be compatible with the other two layers.
The top coat layer is a readymade compound which is black in color and it is completely stable against sun light (UV radiation), high temperature, and oxygen, as well as chemicals.
The first phase: Cleaning the pipes
Prior to application of three layer polyethylene coating, the steel surface of the pipes should be carefully prepared and cleaned. This cleaning phase includes removing all defects of steel surface, cleaning the inside and outside the pipe, abrasive blasting and heating.
So, during this phase, all of the irregularities of the pipe surface and all of the existing damages should be removed and repaired. The metal surface should be free of any kind of contamination including grease, oil, dust, salt, etc. for cleaning the surface, non-oily solvents should be used and kerosene and gasoline should be avoided as cleaners. Any kind of sticker and label should be removes from the pipe surface.
After initial cleaning, you should dry the surface before abrasive blasting. Before starting this phase, the pipes should be heated up to 65 to 85̊ C. while abrasive blasting, all of the created dust should be collected from the pipe surface and inside the pipe completely. Also, the bed should be free of dusts as well.
As it was mentioned, after cleaning the surface, inside the pipe should be cleaned as well by means of various methods like brushing, vacuum cleaning and air blast.
The second phase: Coating process
After cleaning, the prepared pipes should be coated immediately. For this purpose, the pipes should be uniformly heated (deep heat) to be ready for epoxy powder application. Required temperature for this phase should be within a specific range and it should be controlled continuously.
When the pipes are heated enough, the epoxy powder will be applied by means of special spray tools which impose electrostatic charge on the powder. The thickness of this epoxy layer is specified by the producer company and it should be observed carefully and approved by the quality assessment group through accurate testing.
The epoxy powder of the bed can be collected and purified from contaminations and then it can be used again. The quality of the collected epoxy powder should be approved by the quality assessment group.
After epoxy application, the copolymer layer, and after that, the polyethylene layer are applied according to specified thickness. This process should be accomplished in a predefined time and temperature.
There is a specific range of time defined for the second layer application. It should be applied before gel time of the epoxy is finished. This time and required temperature are specified by the producer company. In the same way, time range of the third layer application, as well as required temperature are predefined by the producer company and they should be accurately observed.
During the coating process, high pressure rollers are used in order to prevent any air or void remaining under the coating layers. There should not be any kind of holidays, air bubbles, irregularities, wrinkles, separation of layers or discontinuities observable.
At the end of the pipes, the adhesive is used to seal the coating ends.
The final surface of the three layer polyethylene coating should be natural regarding color, being smooth and regarding gloss. There should not be any kind of defect on the coated surface, such as cuts, voids, wrinkles, pinholes, swellings, etc. defected coated pipes should be put aside.
As it was mentioned before, the producer company predefines minimum and maximum thickness allowed for the coating. So, the thickness of the coating should be examined in different locations of the pipe length by the quality assessment group and it should be within mentioned predefined range.
After coating process, the coated pipes will be cooled down in water for a predefined time.
If there is any kind of problem in the coating, regarding the thickness or defects of the coated surface, the pipes should be put aside to be processed again and the coating should be removed by means of heat and the pipes should be cleaned and coated once more.
The final coated pipes are ultra-resistant and highly durable and they are neutral regarding nature and environmental concerns. Three layer polyethylene coating is the best choice for reinforcement of the steel pipes.
Conclusion:
As it was mentioned above, three Layer Polyethylene Coating is a kind of highly resistant, durable, and efficient coating which is used for various pipeline transferring oil, gas, water and other liquids.
Three layer polyethylene coating, is highly adhesive and tightly adheres to the pipe and protects it in several aspects. Although, it can be removed easily by making use of heat when it is necessary. Three layer polyethylene coating is also very resistant to chemicals. This property allows you to use coated pipelines in any sever condition and in all kind of soils. As this coating is chemical resistant, it is resistant to corrosion as well, and so it is very durable.
When steel pipes are coated with three layer polyethylene coating, they acquire the properties of plastic and their durability and resistance increases significantly and can perform efficiently underground for a very long time.
The best choice for protection of pipelines buried underground is making use of three layer polyethylene coating.
Call our company to get access to the best material with efficient and professional service, in a timely manner. Several tests are down to ensure best quality of the final product.
You can trust our experience and professional experts.
As it is clear by the name, this corrosion resistant coating is made of three compatible layers as they are briefly described below:
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