Pipeline Thermal Insulation/ Pipeline Corrosion Coating



Pipeline Thermal Insulation

Oilfield pipelines are insulated mainly to conserve heat. The need to keep the product in the pipeline at a temperature higher than the ambient could exist for the following reasons including:
  • Preventing formation of gas hydrates
  • Preventing formation of wax or asphaltenes
  • Enhancing product flow properties
  • Increasing cool-down time after shutting down
  • Meeting other operational/process equipment requirements

3LPP anticorrosive three layer polypropylene coating
Source: http://www.izostal.com.pl/gfx/izostal2/_thumbs/en/defaultstronaopisowa/139/1/1/1379194099,mnV-nK6onHGWqK6XYZ0.jpg
In liquefied gas pipelines, such as LNG, insulation is required to maintain the cold temperature of the gas to keep it in a liquid state. Polypropylene, polyethylene, and polyurethane are three base materials widely used in the industry for pipeline insulation. Depending on applications, these base materials are used in different forms resulting in different overall conductivities.p A 3-layer polyproylene applied to pipe surface has a conductivity of 0.13 BTU/hr-ft-8oF, while a 4-layer polypropylene has a conductivity of 0.10 BTU/hr-ft-8F. Solid polypropylene has higher conductivity than polypropylene foam. Polymer syntactic polyurethane has a conductivity of 0.07 BTU/hr-ft-8oF, while glass syntactic polyurethane has a conductivity of 0.09 BTU/hr-ft-8oF. These materials have lower conductivities in dry conditions such as that in pipe-in-pipe applications.

3-layer polyproylene coating
Source: http://www.khipipe.com/wp-content/uploads/2013/02/Three_Layer_Polypropylene_Tape_System.gif
Because of its low thermal conductivity, more and more polyurethane foams are used in deepwater applications. Physical properties of polyurethane foams include density, compressive strength, thermal conductivity, closed cell content, leachable halides, flammability, tensile strength, tensile modulus, and water absorption. The values of these properties vary depending on density of the foam.



Pipeline corrosion coating

Offshore steel pipelines are normally designed for a life ranging from 10 years to 40 years. To enable the pipeline to last for the design life, the pipeline needs to be protected from corrosion both internally and externally. Internal corrosion is related to fluid that is carried by the pipeline, and this topic is not covered here. This article describes the method by which the external corrosion of offshore pipelines may be minimized. A strong adhesive external coating over the whole length of the pipeline will tend to prevent corrosion. However, there is always the possibility of coating damage during handling of the coated pipe either during shipping or during installation.

The properties that are considered desirable for deepwater pipeline coatings are:
  • Resistance to seawater absorption
  • Resistance to chemicals in seawater
  • Resistance to cathodic disbondment
  • Adhesion to the pipe surface
  • Flexibility
  • Impact and abrasion resistance
  • Resistance to weathering
  • Compatibility with cathodic protection
1. Single-layer coating
A single-layer coating is used when the installed pipeline is always in a static, laterally stable condition lying on soils such as clay or sand. Additional layers of coating are used for additional protection, for weight to help the pipeline remain laterally stable on the seabed, or for providing insulation.

The most common choice for single-layer coating for deepwater pipelines is Fusion Bonded Epoxy (FBE). For deepwater pipelines where there is no other requirement on the external coating, FBE is most frequently used. Most deepwater oil and gas transmission lines use FBE as they are extremely cost effective. This coating can be used in conjunction with concrete weight coating. The other coatings that can be used with concrete coating are coal tar enamel and coal tar epoxy and they are used with lower product temperatures. Both of these coatings are bituminous coatings reinforced with fiberglass. However, most bituminous coatings are not desirable due to environmental laws and decreasing efficiency (sagging, cracking, permeation, and chemical deterioration). The FBE field joint coating is carried out using the same coating material as millapplied coating. Further advantages include:
  • Easy to repair
  • Easy for coating application
  • High adhesion to steel
  • Good for pipeline operating temperatures
In the US and UK, FBE coating is preferred for offshore pipelines.

Fusion Bonded Epoxy (FBE) coating
Source: http://www.haihaopiping.com/images/products/Fusion%20Bonded%20Epoxy%20Coating%20System.jpg

2. Multi-layer coating
A multi-layer coating is generally used in cases where the external environment tends to easily wear out the external coating (e.g., pipeline lying on
top of rocky soil, calcareous material, etc.).

- Dual-Layer FBE
Dual-layer FBE coatings are used when additional protection is required for the outer layer such as high temperature, abrasion resistance, etc. For deepwater trunklines the high temperature of the internal fluid dissipates rapidly reaching ambient within a few miles. Therefore, the need for such coatings is limited for SCRs at the touchdown area where abrasion is high and an additional coating with high abrasion resistance is used. The Duval system consists of an FBE base coat (20 mils) bonded to a polypropylene coating (20 mils). The polypropylene layer provides mechanical protection.

Dual-layer FBE
Source: http://www.nbfangfu.com/login/eWebEditor/UploadFile/2009722152935779.GIF
 - Three-Layer
Three-layer PP coating consists of an epoxy or FBE, a thermoplastic adhesive coating and a polypropylene top coat. The polyethylene (PE) and polypropylene (PP) coatings are extruded coatings. These coatings are used for additional protection against corrosion and are commonly used for dynamic systems like steel catenary risers and where the temperature of the internal fluid is high. These pipe coatings are frequently used in pipelines that are installed by the reeling method. The field joint coating for the three-layer systems is more difficult to apply and takes a longer time. However, in Europe, PE and PP coatings are preferred because of their high dielectric strength, water tightness,
thickness, and very low CP current requirement.
Three-layer polypropylene
Source: http://globalpipesfield.com/wp-content/uploads/2013/04/3LAYERS2a.jpg

- Concrete Weight Coating
Concrete weight coating is used when stability of the pipeline on the seabed is an issue. The two common densities of concrete that are used are 140 lbs/cu. ft and 190 lbs/cu. ft. Higher density is obtained by adding iron ore to the concrete mix. Recently, higher density iron ore has been used to obtain concrete density ranging from 275 to 300 lbs/cu. ft for the Ormen Lange pipeline in the North Sea.

Concrete weight coating
Source: http://www.offshoreenergytoday.com/wp-content/uploads/2012/01/Trinidad-ShawCor-Providing-Weight-Coatings-for-Technips-Offshore-Pipeline-Project.jpg



Source:
Offshore pipelines - Dr. Boyun Guo (2005)



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