Thermal Protection Systems for Piping and Equipment
Red Seal Practice study guide with diagrams.
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:
Q = heat flow (W)
k = thermal conductivity of the material (W/m·°C)
A = area perpendicular to the heat flow (m²)
ΔT = temperature difference between the two faces (°C)
L = material thickness (m)
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:
ε = surface emissivity (dimensionless, between 0 and 1)
T₁, T₂ = absolute temperatures of the surfaces (K)
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:
Rᵢ = internal convection resistance
R₁, R₂... = conduction resistances of the insulation layers
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:
Material
Thermal Conductivity (W/m·°C)
Mineral wool (rock wool)
0.035 – 0.045
Fiberglass
0.032 – 0.040
Expanded perlite
0.045 – 0.060
Calcium silicate
0.055 – 0.070
Polyurethane foam
0.022 – 0.028
Extruded polystyrene foam
0.028 – 0.033
Ceramic fiber
0.050 – 0.080 (at high temperature)
Cellular glass
0.040 – 0.055
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:
42.Thermal insulation: Limits heat transfer (energy conservation, process temperature control).
43.Freeze protection: Maintains fluid temperature above the freezing point.
44.Condensation control: Maintains surface temperature above the dew point to prevent condensation on cold surfaces.
45.Personnel protection: Limits surface temperature to safe values to prevent burns (generally 60 °C maximum).
Piping Insulation
For piping, insulation can be applied as:
Rigid shells (preformed): For pipes with nominal diameters from ½ in to 24 in and larger. Available in mineral wool, calcium silicate, cellular glass, etc.
Felts and blankets: For large diameters or complex geometries.
Loose-fill insulation: For confined spaces or irregular shapes.
Equipment Insulation
For equipment (tanks, boilers, heat exchangers), common methods include:
Each material has a maximum service temperature. Beyond this, the material degrades, melts, or burns.
Material
Maximum Service Temperature (°C)
Fiberglass
230 – 260
Rock wool
650 – 750
Calcium silicate
650 – 1000
Expanded perlite
650 – 870
Ceramic fiber
1260 – 1430
Cellular glass
430 – 480
Polyurethane foam
100 – 120
Polyisocyanurate foam
120 – 150
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.
Material
μ Factor
Cellular glass
∞ (impermeable)
Polyurethane foam
30 – 100
Extruded polystyrene foam
80 – 200
Mineral wool
1 – 2
Fiberglass
1 – 2
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:
Class A: Flame spread rating 0 – 25
Class B: Rating 26 – 75
Class C: Rating 76 – 200
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
Material
Permeance (ng/Pa·s·m²)
Typical Use
Aluminum foil (0.025 mm)
0.000
High temperature
Polyethylene sheet (0.15 mm)
0.003 – 0.006
Moderate temperature
Reinforced kraft paper
0.02 – 0.06
Duct insulation
Vapor barrier paint
0.1 – 0.5
Touch-up, repair
Bituminous membrane
0.001 – 0.01
Underground applications
Joints and Overlaps
Vapor barrier joints must be sealed with a compatible adhesive. Minimum overlaps are:
Longitudinal: 50 mm minimum
Circumferential: 75 mm minimum
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:
Mechanical damage (impact, abrasion)
Moisture and weather
UV rays (for outdoor applications)
Fire (for certain types of jackets)
Types of Jackets
Type
Material
Typical Thickness
Application
Metal sheet
Aluminum, galvanized steel, stainless steel
0.4 – 0.8 mm
Exterior, high durability
Fiberglass reinforced plastic (FRP)
Resin + fiberglass
1.5 – 3 mm
Exterior, chemical resistance
Coated fabric
Glass cloth + coating
0.5 – 1 mm
Interior, piping
Mastic
Asphalt-based or acrylic compound
1 – 3 mm
Complex shapes, fittings
Kraft paper
Paper + aluminum foil
0.1 – 0.3 mm
Interior, ducts
Metal Jacket Installation Rules
Longitudinal overlaps must be oriented to shed water (generally at 4 o'clock or 8 o'clock on horizontal pipes).
Circumferential overlaps must be at least 75 mm.
Fasteners (screws, rivets) must be spaced 150 to 300 mm apart.
Expansion joints must be provided every 6 to 9 meters on pipes subject to temperature variations.
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:
Tₛ = outer surface temperature
Tₐ = ambient air temperature
Tₚ = process temperature (cold fluid)
Rₒ = external convection resistance
Rₜₒₜ = total thermal resistance
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:
Service Temperature (°C)
Minimum Thickness (mm)
4 – 10 (refrigeration)
50 – 75
10 – 50 (air conditioning)
25 – 50
50 – 120 (hot water)
25 – 50
120 – 200 (low-pressure steam)
50 – 75
200 – 350 (medium-pressure steam)
75 – 100
350 – 550 (high-pressure steam)
100 – 150
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:
120.Inner radius of insulation: r₁ = 0.054 m (outer radius of pipe)
121.Outer radius of insulation: r₂ = 0.054 + 0.050 = 0.104 m
CSA B149.1: Natural Gas and Propane Installation Code — Rule 6.24 regarding insulation of gas piping (specific requirements for buried pipes).
National Building Code of Canada (NBC): Thermal protection requirements for buildings (Section 9.25 for insulation).
National Plumbing Code of Canada (NPC): Insulation requirements for hot and cold water piping.
CAN/ULC-S102: Test method for flame spread and smoke development.
CAN/ULC-S701: Standard for expanded polystyrene thermal insulation.
CSA Z275: Standard on confined space work (relevant for installing insulation in confined spaces).
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:
Resistant to moisture
Non-corrosive to the metal
Capable of withstanding soil pressure
Applied without gaps or voids
Installation Procedures
Surface Preparation
Before applying insulation, the surface must be:
146.Clean: Free of rust, scale, oil, or dirt.
147.Dry: Any residual moisture will compromise adhesion and promote corrosion under insulation.
148.Protected: A corrosion-resistant primer coat may be necessary, particularly for carbon steel piping.
Application of Preformed Shells
150.Verify that the shell diameter matches the outer diameter of the pipe.
151.Apply shells in a staggered pattern (longitudinal joints must not be aligned from one layer to the next).
152.Secure the shells with adhesive tape or metal bands.
153.For horizontal pipes, start at the bottom and work upward.
154.For vertical pipes, start at the bottom so that the upper shells rest on the lower ones.
Insulating Fittings and Valves
Fittings (elbows, tees, reducers) and valves require special attention:
Elbows: Use miter-cut shell segments or preformed elbow shells.
Valves: Use removable boxes or custom blankets to allow access.
Pipe supports: Insulation must be interrupted at supports to prevent crushing. Use treated wood blocks or high compressive strength insulation inserts.
Equipment Insulation
For tanks and large equipment:
162.Install welded or adhesive-applied studs on the surface.
163.Apply insulation panels or blankets, securing them with washers and nuts on the studs.
164.Cover with the selected jacket.
165.Seal all joints with a compatible mastic.
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:
169.Steam tracing: Steam tubes installed along the piping, beneath the insulation.
170.Electric tracing: Self-regulating or constant-wattage heating cables.
Installation Rules
Tracing must be installed before the insulation.
Insulation must be applied over the tracing, without gaps.
Electric cables must comply with the requirements of the Canadian Electrical Code, Part I (CE Code).
Steam tracing must be installed with a slope to allow condensate drainage.
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
Temperature cycling (wetting/drying alternation)
Temperatures between 0 °C and 120 °C (critical zone)
Absorbent insulations (mineral wools)
Absence or failure of the vapor barrier
Damaged jackets
Preventive Measures
186.Use high-performance corrosion-resistant coatings on the metal surface.
187.Choose insulations with low water absorption (cellular glass, polyurethane foam).
188.Ensure the integrity of the vapor barrier and jackets.
189.Install protective caps at pipe ends.
190.Elevate supports to avoid contact with standing water.
Safety Considerations
Workplace Safety
Respiratory protection: Mineral wools and ceramic fibers can irritate the respiratory tract. Use at minimum an N95 respirator.
Skin protection: Wear gloves and long-sleeved clothing to prevent skin irritation.
Work at heights: Use compliant scaffolding and safety harnesses.
Confined spaces: Follow the requirements of CSA Z275 for confined space work.
Asbestos: Older buildings and equipment may contain asbestos. Any suspicion of asbestos requires stopping work and calling in a certified professional.
Fire Safety
Combustible insulations must be protected by fire barriers compliant with the NBC.
Welding work near insulation must be done with hot work permits.
Insulating materials must be stored away from ignition sources.
Pitfalls to Avoid
203.Confusing thermal conductivity and thermal resistance: Conductivity (k) is a material property; resistance (R) depends on thickness and geometry. R = L/k for a flat wall.
204.Forgetting that k varies with temperature: Using the k value at ambient temperature for a system at 400 °C leads to significant calculation errors.
205.Placing the vapor barrier on the wrong side: The vapor barrier always goes on the warm side. An error here causes massive condensation within the insulation.
206.Neglecting thermal bridges: Uninsulated metal supports, branch connections, and valves create thermal bridges that reduce overall system efficiency.
207.Ignoring the minimum thickness for personnel protection: Even if the economic thickness is lower, the surface temperature must not exceed 60 °C in accessible areas.
208.Using absorbent insulation without an adequate vapor barrier: On cold systems, the absence of a vapor barrier or a poorly sealed vapor barrier inevitably leads to condensation and degradation.
209.Not accounting for thermal expansion: Hot pipes expand. The insulation and jacket must accommodate this expansion without deforming or cracking.
210.Confusing units: Calculations must use consistent units. Convert inches to meters, BTU to watts, etc.
211.Forgetting code requirements for gas piping: CSA B149.1 has specific requirements for insulating buried gas pipes. Failure to comply is a serious violation.
212.Neglecting corrosion under insulation protection: On carbon steel piping, applying a corrosion-resistant primer before insulation is an essential practice.
Summary
Thermal protection is based on mastering the three modes of heat transfer: conduction, convection, and radiation.
Thermal conductivity (k) is the key property of an insulator; the lower it is, the better the performance.
The total thermal resistance of a system is the sum of the resistances of each layer, including convection resistances.
The four functions of insulation are: energy conservation, freeze protection, condensation control, and personnel protection.
The vapor barrier must always be placed on the warm side of the insulation.
Jackets protect the insulation against mechanical damage, moisture, and fire.
Thickness calculations must consider service temperature, ambient temperature, relative humidity, and regulatory requirements.
Applicable Canadian standards include CSA B52, CSA B149.1, the NBC, and the Canadian Electrical Code, Part I (CE Code).
Corrosion under insulation is a major risk that must be prevented with appropriate coatings and low water absorption insulations.
Workplace safety is paramount: respiratory protection, skin protection, and compliance with confined space procedures.
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.
