ISO 21809-1 applies to buried or submerged pipeline systems in the oil and gas industry and specifies the requirements for the external corrosion protection coatings 3LPE and 3LPP for welded and seamless steel pipes.
There are three classes of surfacing materials, depending on the type of surfacing material:
A: LDPE (low-density polyethylene);
B: MDPE/HDPE (medium-density polyethylene)/(high-density polyethylene);
C: PP (Polypropylene).
The density requirements for each material are described in detail in the following subsection on the requirements for the three raw materials.
| Coating class | Top layer material | Design temperature (°C) |
| A | LDPE | -20 to + 60 |
| B | MDPE/HDPE | -40 to + 80 |
| C | PP | -20 to + 110 |
The coating system shall consist of three layers:
1st layer: epoxy(liquid or powder);
2nd layer: adhesive;
3rd layer: PE/PP top layer applied by extrusion.
If required, a rough coat can be applied to increase slip resistance. Especially where improved grip and reduced risk of sliding are required.
Epoxy Resin Layer Thickness
Maximum 400 um
Minimum: Liquid epoxу: minimum 50um; FBE: minimum125um.
Adhesive Layer Thickness
Minimum 150um on pipe body
Total Coating Thickness
The thickness level of the anti-corrosion layer is changed with the site load and the pipe's weight, and the anti-corrosion layer's thickness level should be selected according to the construction conditions, pipe laying method, use conditions, and pipe size.
Pm is the weight of the steel pipe per meter.
which can be queried by consulting the corresponding weight table of the steel pipe standard, or by the formula:
Pm=(D-T)×T×0.02466
D is the specified outside diameter, expressed in mm;
T is the specified wall thickness, expressed in mm;
Requirements for the Epoxy Material
Requirements for the Adhesive Material
Requirements for PE/PP Top Layer
The anti-corrosion process can be roughly divided into:
1. Surface preparation;
2. Coating application
3. Cooling
4. Cutback
5. Marking
6. Finished product inspection
1. Surface Preparation
Similar requirements are found in the SSPC and NACE standards, and the following is a general correspondence:
| ISO 8501-1 | NACE | SSPC-SP | Designation |
| Sa 2.5 | 2 | 10 | Near-white metal blast cleaning |
| Sa 3 | 1 | 5 | White metal blast cleaning |
Please note that the effect of Sa 2.5 is not fixed depending on the corrosion grade of the steel pipe, which is categorized as A, B, C, and D, corresponding to 4 effects.
2. Coating Application
Ensure that the preheating temperature and line speed of the steel pipe in the coating process are appropriate to achieve full curing of the powder coating and to ensure the adhesion of the coating as well as to control the thickness of the coating.
The thickness of the corrosion protection layer is also related to the parameters of the coating equipment.
3. Cooling
The applied coating shall be cooled to a temperature that prevents handling damage during finishing and final inspection.
Generally, the cooling temperature of 3LPE is no more than 60℃, and the cooling temperature of 3LPP will be a little higher.
4. Cutback
A certain length of coating should be removed from both ends of the pipe and the corrosion protection layer should not be beveled at an angle of more than 30° to prevent possible damage to the corrosion protection coating during welding.
5. Marking
Compliance with standards and customer requirements.
These markings should be stenciled or painted to ensure that the lettering is clear and does not fade.
6. Finished Product Inspection
Comprehensive inspection of finished anti-corrosion pipes to meet the requirements of ISO 21809-1.
3LPE Applications
3LPE coatings offer high chemical resistance, excellent mechanical protection as well as good durability, and low maintenance costs.
It is suitable for buried or underwater pipelines that require high corrosion resistance and mechanical protection in soil and water environments.
Commonly used in piping systems for the transportation of oil, gas, and water.
3LPP Applications
3LPP coatings have higher temperature resistance and excellent chemical stability than polyethylene. However, it can become brittle at low temperatures.
Suitable for higher temperatures and more demanding environments, such as piping in hotter areas or near chemical processing plants.
Typically used in oil and gas piping systems where high-temperature performance is required.
DIN 30670: Polyethylene coatings of steel pipes and fittings.
This is a German industry standard specifically for polyethylene coatings for steel pipes and their fittings.
DIN 30678: Polypropylene coatings on steel pipes.
Polypropylene coating system specifically for steel pipes.
GB/T 23257: Polyethylene coating technology standards on buried steel pipeline.
This is a national standard in China covering polyethylene coating technology for buried steel pipelines.
CSA Z245.21: Plant-applied external coatings for steel pipe.
This is a Canadian Standards Association (CSA) standard that specifies requirements for external polyethylene coatings used to protect steel pipe.
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