Thermal Protection Systems for Piping and Equipment

Thermal Protection Systems for Piping and Equipment

Chapter Introduction

This chapter covers the principles, materials, installation methods, and calculations related to thermal protection systems for piping and equipment. As a journeyperson insulator/heat and frost insulator, you must master not only application techniques, but also the understanding of the physical phenomena involved, the requirements of Canadian standards, and material selection criteria. This chapter is designed to prepare you directly for Red Seal exam questions.

Fundamental Principles of Heat Transfer

The Three Modes of Transfer

Thermal protection aims to control heat transfer between a fluid (hot or cold) and the environment. Three modes of transfer must be understood:

Conduction: Heat transfer through a solid material. The amount of heat transferred by conduction is governed by Fourier's law:

Q = k × A × ΔT / L

Where:

Convection: Heat transfer between a surface and a moving fluid (air, water). It is described by Newton's law of cooling:

Q = h × A × ΔT

Where h is the convection coefficient (W/m²·°C). This coefficient depends on fluid velocity, surface geometry, and fluid properties.

Radiation: Heat transfer by electromagnetic waves. It is described by the Stefan-Boltzmann law:

Q = ε × σ × A × (T₁⁴ − T₂⁴)

Where:

Total Thermal Resistance

In practice, heat transfer through an insulated system involves all three modes simultaneously. The concept of total thermal resistance (Rₜₒₜ) is then used:

Rₜₒₜ = Rᵢ + R₁ + R₂ + ... + Rₙ + Rₒ

Where:

The resistance of a cylindrical layer (pipe) is calculated as:

R = ln(r₂/r₁) / (2 × π × k × L)

Where r₁ and r₂ are the inner and outer radii of the insulation layer.

Thermal Conductivity of Insulating Materials

Thermal conductivity (k) is the most important property of an insulator. The lower the k value, the better the insulating performance. Typical values at 24 °C:

Important: Thermal conductivity varies with temperature. For high-temperature applications, use the k value at the mean operating temperature, not at ambient temperature.

Types of Thermal Protection Systems

Classification by Function

Thermal protection systems are classified into four functional categories:

Piping Insulation

For piping, insulation can be applied as:

Equipment Insulation

For equipment (tanks, boilers, heat exchangers), common methods include:

Insulating Material Selection Criteria

Service Temperature

Each material has a maximum service temperature. Beyond this, the material degrades, melts, or burns.

Compressive Strength

For applications where the insulation must support loads (pedestrian traffic, heavy equipment), compressive strength is critical. Cellular glass and polyisocyanurate offer high strength (400 – 700 kPa). Mineral wools have lower strength (20 – 100 kPa).

Moisture Resistance and Vapor Permeability

Moisture significantly degrades insulation performance. Water has a thermal conductivity of approximately 0.6 W/m·°C, which is 15 to 20 times higher than that of insulation. Wet insulation loses 50% to 90% of its effectiveness.

The water vapor diffusion resistance factor (μ) indicates a material's ability to resist the passage of vapor. A high μ means a better barrier.

Fire Reaction

Insulating materials must comply with the requirements of the National Building Code of Canada (NBC) and CAN/ULC-S102 standards (flame spread and smoke development test). Classifications are:

For interior applications, Class A is generally required. Jackets and finishes can improve the fire classification of an insulator.

Vapor Barriers and Sealing Barriers

Role of the Vapor Barrier

The vapor barrier is a critical component of insulation systems for low-temperature applications (refrigeration, air conditioning). Its role is to prevent water vapor from penetrating the insulation and condensing within it.

The fundamental rule: the vapor barrier must be placed on the warm side of the insulation (the side where vapor pressure is highest).

Vapor Barrier Materials

Joints and Overlaps

Vapor barrier joints must be sealed with a compatible adhesive. Minimum overlaps are:

Any penetrations (supports, branch connections, valves) must be carefully sealed with mastic or a sealing compound.

Jackets and Finishes

Functions of Jackets

The outer jacket (cladding) protects the insulation against:

Types of Jackets

Metal Jacket Installation Rules

Insulation Thickness Calculations

Economic Thickness

The economic insulation thickness is the one that minimizes total cost (insulation cost + energy loss cost) over the system's service life. The full calculation involves:

Total cost = Insulation cost + Annual heat loss cost × Service life factor

The economic thickness is found by plotting total cost against thickness and identifying the minimum.

Thickness for Condensation Control

For cold surfaces, the minimum thickness is calculated so that the outer surface temperature of the insulation is above the dew point of the ambient air.

The simplified formula:

Tₛ = Tₐ − (Tₐ − Tₚ) × Rₒ / Rₜₒₜ

Where:

To prevent condensation, Tₛ must be greater than Tᵣ (dew point). A safety margin of 2 to 3 °C is recommended.

Table of Recommended Minimum Thicknesses

The Canadian Energy Code and industry guides recommend minimum thicknesses based on service temperature:

Calculation Example

Problem: A 100 mm nominal diameter steam pipe carries steam at 180 °C. The ambient temperature is 25 °C. The insulation is rock wool (k = 0.040 W/m·°C). Calculate the heat loss per meter of pipe with a 50 mm insulation thickness.

Solution:

Applicable Standards and Codes

Main Canadian Standards

Canadian Electrical Code Requirements

The Canadian Electrical Code, Part I (CE Code) (C22.1) contains requirements regarding clearances between insulating materials and electrical conductors. Rule 8-200 requires that combustible insulating materials be kept at a minimum distance from bare live conductors. In practice, maintain a clearance of at least 25 mm between insulation and electrical conductors.

CSA B149.1 Requirements for Gas Piping

Rule 6.24 of CSA B149.1 specifies that buried gas piping must be protected against corrosion. The insulation used for this protection must be:

Installation Procedures

Surface Preparation

Before applying insulation, the surface must be:

Application of Preformed Shells

Insulating Fittings and Valves

Fittings (elbows, tees, reducers) and valves require special attention:

Equipment Insulation

For tanks and large equipment:

Heat Tracing

Heat Tracing Principles

Heat tracing is used to maintain the temperature of a fluid in piping when insulation alone is insufficient. Two main types:

Installation Rules

Corrosion Under Insulation (CUI) Control

The Problem

Corrosion under insulation (CUI) is a major cause of failure in industrial piping. It occurs when water penetrates the insulation and remains in contact with the metal surface.

Factors Promoting CUI

Preventive Measures

Safety Considerations

Workplace Safety

Fire Safety

Pitfalls to Avoid

Summary

Exam Tip: Red Seal exam questions on this topic frequently focus on selecting the appropriate material based on service temperature, correct vapor barrier placement, and heat loss calculations. Master the maximum temperature tables and the basic formulas. When you encounter a question about insulation thickness, always check whether it concerns economic thickness, condensation control thickness, or personnel protection thickness — the answer differs depending on the objective.