Documentations

Insulation Coating

For production risers, insulation coatings are applied to maintain the temperature of the fluid within the riser. A multi-layer polypropylene (PP) or multi-layer polyethylene (PE) thermal insulation coating system should be designed to meet the necessary insulation requirements.

5LPP

A five-layer coating system is proposed for the parent joint. The coating layers, from inside to outside, are described as follows:

  • Layer 1: FBE - anti-corrosion
  • Layer 2: PP Adhesive - anti-corrosion
  • Layer 3: Solid PP - anti-corrosion
  • Layer 4: GSPP or GSPU - thermal insulation
  • Layer 5: PP Shield - mechanical and UV protection

U Value

To achive the target overall heat transfer coefficient (U-value), the thickness of the GSPP (coating for thermal insulation) is calculated to meet the specified insulation requirements. The U-value calculation for the thermal insulation coating system is based on the following equation. \[U = {1 \over { {R_{ref}\over {R_i\cdot h_i} }+{R_{ref}\over k_1} ln\left({OR_1\over IR_1}\right)+{R_{ref}\over k_2} ln\left({OR_2\over IR_2}\right)+ ... + {R_{ref}\over k_n} ln\left({OR_n \over IR_n }\right)+{R_{ref}\over {R_o\cdot h_o} } } } \tag{1}\label{eq1} \]

where

  • \(h_i\) = convection heat transfer coefficient of internal fluid,
  • \(h_o\) = convection heat transfer coefficient of external fluid (seawater),
  • \(R_i\) = inner radius of steel pipe,
  • \(R_o\) = outer radius of steel pipe,
  • \(R_{ref}\) = reference radius, can be either steel pipe inner radius (\(R_i\)) or outer radius (\(R_o\)),
  • \(OR_i \) = outer radius of layer i (i = 1,..n),
  • \(IR_i \) = inner radius of layer i (i = 1,..n), and
  • \(k_i \) = thermal conductivity of layer i (i = 1,..n).

Heat resistance factors from internal and external fluid are ignored in this calculation.

The following figure illustrates an example of U-values varying with different thermal insulation thicknesses. The data includes both calculated values and benchmarks from previous projects.

In-Line Onset
Figure 1: U-values with Varing Thermal Insulation Thickness

3LPE/3LPP

a 3LPE (three-layer polyethylene) or 3LPP (three-layer polypropylene) coating is proposed for anti-corrosion protection. The coating system, from inside to outside, is described as follows:

  • Layer 1: FBE - anti-corrosion
  • Layer 2: PP Adhesive - anti-corrosion
  • Layer 3: Solid PE or PP - anti-corrosion

References
  1. ISO 21809-1, Petroleum and Natural Gas Industries - External Coatings for Buried or Submerged Pipelines Used in Pipeline Transportation Systems - Part 1: Polyolefin Coatings (3-layer PE and 3-layer PP)
  2. ISO 21809-2, Petroleum and Natural Gas Industries - External Coatings for Buried or Submerged Pipelines Used in Pipeline Transportation Systems - Part 2: Fusion-bonded Epoxy Coatings
  3. ISO 21809-3, Petroleum and Natural Gas Industries - External Coatings for Buried or Submerged Pipelines Used in Pipeline Transportation Systems - Part 3: Field Joint Coatings
  4. DNV-RP-F106 Factory Applied External Pipeline Coatings for Corrosion Control
  5. DNV-RP-F102 Pipeline Field Joint Coating and Field Repair of Linepipe Coating
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