Tank Heating: Industrial Heat Tracing Solutions
Tank Heating: Industrial Heat Tracing Solutions
Tank Heating: Industrial Heat Tracing Solutions
This step-by-step design guide provides the tools necessary to design a tank
heating system for temperature maintenance using electric heating cables or tank
heating pads. For design assistance, contact your Pentair Industrial Heat Tracing
Solutions representative or phone Pentair at (800) 545-6258. Also, visit our web
site at www.pentairthermal.com.
Contents
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Self-Regulating Heating Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Power-Limiting Heating Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Mineral Insulated Heating Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Tank Heating Pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Tank Tracing Design and Product Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Tank Heat Loss Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Introduction
Pentair provides a wide selection of heat-tracing solutions for tanks and vessels.
Typical applications for electrical heat tracing of tanks and vessels include:
• Freeze protection of low and medium viscosity fluids (e.g., water, ammonia)
• Temperature maintenance for medium viscosity fluids (e.g., oils, resins)
• Crystallization prevention (e.g., caustic soda)
• Condensation prevention (e.g., fly ash in conical bases of silos)
Contact Pentair for heat-up applications, hazardous locations, heat tracing of high
viscosity fluids (e.g. heavy oils), applications where agitation is used, and other
nonstandard applications.
Tank heating applications can be quite varied. For this reason, Pentair offers a wide
range of technologies to optimize your tank and vessel heat-tracing system.
• Self-regulating heating cables
• Power-limiting heating cables
• Tank heating pads
• Mineral insulated heating cables
Raychem brand self-regulating heating cables (BTV, QTVR, XTV, and KTV) are ideal for
tank heating when design and installation flexibility are required. The benefits include:
Easy installation Because of parallel circuitry and flat cable design, Raychem
self-regulating heating cables are easy to handle and install. They can be cut to
any length on site and overlapped without the risk of overheating. Raychem cables
readily accommodate design adjustments between specifications and actual on-site
installation needs.
Approvals Pentair self-regulating systems are approved and certified for use in
nonhazardous and hazardous locations by many agencies, including FM , CSA, UL,
PTB, Baseefa, NEPSI, DNV, ABS and many more.
Raychem brand power-limiting heating cables (VPL) feature high power output at
high maintain temperatures. These flexible heating cables are rated for maintain
temperatures up to 455°F (235°C) and exposure temperatures (power off) to 500°F
(260°C). Power-limiting heating cables feature:
Easy installation Cables can be cut to length and terminated in the field.
Uniform distribution of heat Heat is evenly and widely distributed over the heat-traced
surface.
Approvals Pentair power-limiting systems are approved and certified for use in
nonhazardous and hazardous locations by many agencies, including FM , CSA, UL,
PTB, Baseefa, NEPSI, DNV, ABS and many more.
VPL
Raychem brand mineral insulated heating cables (MI) offer a very reliable solution
and are recommended for maintain temperatures above 300°F (150°C) or where
exposure temperatures exceed 500°F (260°C). Raychem MI heating cables feature:
Superior toughness Raychem MI heating cables and nonheating cold leads are
manufactured with a seamless sheath of Alloy 825 and have proven their reliability in
over 40 years of service. MI provides superior toughness in dynamic cut-through
and tough mechanical environments.
Approvals Pentair mineral insulated heating systems meet the requirements of the
U.S. National Electrical Code and the Canadian Electrical Code.
Pentair MI systems are approved for use in hazardous locations. Based on the
application, temperature ID number (T-rating) can be established by calculating the
maximum sheath temperature. Contact Pentair for assistance.
Alloy 825
Raychem brand tank heating pads (RHS) are recommended when high wattage
density is required. The RHS system provides heat to selected areas on the tank.
The heat is then distributed through convection in the fluid (natural or agitated).
RHS is built from durable components for use on tanks in industrial applications.
The heating pads have a constant power output and are available with two power
densities, making them suitable for both metal (lined and unlined) and plastic tanks.
RHS tank heating pads have been designed to include the following benefits:
Easy installation Raychem RHS tank heating pads can easily be installed by a single
person.
Approvals FM Approvals (FM) and CSA Group (CSA) have approved RHS tank heating
pads for both nonhazardous and hazardous locations.
Additional technical information can be found in the RHS data sheet (H56842).
Nichrome
heating wire
Liquid-tight electrical
conduit exiting a low-
profile junction box
RHS
The stainless steel grounding plane is flexible enough to contour to most tank
surfaces, and it is oversized to protect the heating elements and maximize contact
with the tank.
RHS can be used for maintain temperatures up to 200°F (93°C) and maximum
exposure temperatures of 366°F (186°C). For technical details, refer to the RHS data
sheet. Data sheets can be found on the Pentair web site, www.pentairthermal.com,
or the Technical data sheet section of the Industrial Heat Tracing Solutions Products
& Services Catalogue (H56550).
Overview
Follow the five steps below to select the heating products and create a bill of
materials for your tank application. If your tank application requires heat-up or
condensation prevention, contact Pentair for assistance.
Uses
• Tanks containing temperature-sensitive fluids
• Tank materials such as PVC or PE
• Applications requiring uniform heating (condensation prevention)
• Tanks with unusual shapes to trace
Advantages
• Very flexible design and installation
–– Cables can be installed on any type of tank surface
–– Cables adapt to any shape or surface
–– Cables allow tracing with more power on high heat loss areas — just reduce
the spacing between the heating cables in those areas
–– Cables can be cut to length in the field
• Even heat distribution due to larger heated surface
• Very smooth heating for tank walls with a low withstand temperature
Uses
• Tanks containing fluids that are less temperature sensitive
• Tanks with high heat loss, and where flexibility in installation is a premium
• Tanks with a maintain temperature between 250°F (121°C) and 300°F (150°C)
Advantages
• Very flexible design and installation
–– Cables can be installed on any type of tank surface
–– Cables adapt to any shape or surface
–– Cables allow tracing with more power on high heat loss areas — just reduce
the spacing between the heating cables in those areas
–– Cables can be cut to length in the field
• Even heat distribution due to larger heated surface
• Very smooth heating for tank walls with a low withstand temperature
Uses
• Maintain temperatures above 300°F (150°C)
• Exposure temperatures above 500°F (260°C)
• Tanks with high heat loss or high power requirements at elevated temperatures
Advantages
• Flexible design and installation
–– Cables can be installed on any type of tank surface
–– Cables can adapt to any shape or surface
–– Cables allow tracing with more power on high heat-loss areas — just reduce
the spacing between the heating cables in those areas
• Even heat distribution due to larger heated surface
• Capability for high power output and density
Uses
• Tanks containing fluids that are not temperature sensitive
• Tanks where the surface is space-constrained
• Tanks with high heat loss
• Fluids with low viscosity (such as water or light oil)
Advantages
• Lower installation cost
• Capability for high power output and watt density
overview
• Orientation of tank
• Spacing and arrangement of the heating cables
• Traced surface
–– Vertical cylindrical tanks
–– Horizontal cylindrical tanks
–– Conical outlets
• Thermal design for heating cables
–– Determine heating cable compatible with your tank application
–– Select heating cable with the lowest maximum exposure temperature
–– Adjust for aluminum tape attachment
–– Determine minimum required length of heating cable
–– Determine cable distribution
• Electrical design of heating cable
–– Determine maximum allowable circuit length of heating cable
–– Adjust for aluminum tape attachment
–– Ground-fault protection
• Heating cable component selection
Conical outlets
Conical outlets of vessels are often traced to prevent condensation inside. We
recommend that the entire surface of the conical outlet be traced and additional
tracing is recommended on heat sinks, such as fixings/supports. Heat sinks should
be thermally isolated. Because the surface area of the conical outlet is often much
smaller than the rest of the vessel, it may be necessary to extend the tracing beyond
the conical area in order to fully compensate for the heat loss.
Determine the heating cable families compatible with your tank application
To select a heating cable that is compatible with your application, familiarize yourself
with the selection process for pipes as outlined in Self-Regulating Cables design
guide (H56882) and Power-Limiting Cables design guide (H56883). Considering
factors such as exposure temperature, maintain temperature, wall material,
hazardous location requirements, etc., list all heating cable families that would be
compatible with your tank application — e.g., BTV, QTVR, XTV, KTV, VPL. The power
outputs for the different heating cables are found in the Self-Regulating Cables and
Power-Limiting Cables design guides.
Select the heating cable with the lowest maximum exposure temperature
Use the heating cable with the lowest possible maximum exposure temperature.
Within each heating cable family, start with the cable that has the highest power
output.
Multiply the power output at the maintain temperature (Pheater) by the appropriate
adjustment factor ƒadj from Table 2 above.
Formula: Padj = Pheater x ƒadj
Next, determine how to distribute cable over the surface you wish to trace. An
average spacing of the heating cable (Taverage) can be calculated by dividing the
traced surface (Straced) by the total length of the heating cable (Lheater).
Straced (ft2)
Formula Taverage = (round up)
Lheater (ft)
Ground-fault protection
To minimize the danger of fire from sustained electrical arcing if the heating
cable is damaged or improperly installed, and to comply with the requirements of
Pentair, agency certifications, and national electrical codes, ground-fault equipment
protection must be used on each heating cable branch circuit. Arcing may not be
stopped by conventional circuit protection. Many Raychem control and monitoring
systems meet the ground-fault protection requirement.
E-100
E-100-A E-100-L
WARNING: Fire hazard Table 4 Connection Kit and Accessory Selection for Self-
To prevent fire or shock, Raychem Regulating and Power-Limiting Cables
brand specified connection kits Description Catalog number
must be used. Do not substitute
parts or use vinyl electrical tape. Connection kits
Power connection kit (not shown) JBS-100-A
Power connection kit with light JBS-100-L-A
Splice connection (not shown) S-150 (not for use with VPL)
End seal
Below insulation E-150 (not for use with VPL)
Above insulation E-100-A
Above insulation, with light E-100-L-A (100-277 V)
Accessories
Aluminum tape AT-180
Labels ETL
Support bracket SB-100-T
Controls
Thermostat (see Control and Monitoring design guide (H56889))
Tank Tracing Step 4b Product selection for mineral insulated heating cables
1. Gather information
2. Calculate tank For MI product selection and design, refer to Mineral Insulated Heating Cables
heat loss design guide (H56884) or contact your Pentair representative.
3. Choose heating
technology
4. Product selection
5. Select thermostatic
control
Tank material and power density determine which RHS tank heater series to select.
The number of heaters required depends on the amount of heat distribution the
application requires. A large number of low-power pads will disperse the heat better
than a few high-power heaters. Pentair recommends distributing the heat over as
much wall surface as is economically feasible.
Note: Pentair does not recommend the use of tank heating pads for applications
with:
• Highly temperature-sensitive fluids
• High-viscosity fluids
• Double-wall tanks
• Tank diameters of less than four feet
• A requirement for uniform heating
• A location where an installation temperature above 0°F (–18°C) cannot be
assured.
Tank Material
Table 1 on page 6, indicates the heater to select based on tank type, heat loss,
and surface area available.
Metal tanks
RHS-H series heaters are used for metal tanks. RHS-H heaters have a power density
of 1.9 W/in2 at the specified voltage with integrated thermostatic over-temperature
protection.
Table 5 lists the RHS-H configurations available. To determine the number of heaters
required, divide the final design heat loss for the tank by the heater’s power output.
Determine the maximum fluid maintain temperature, Tf. Enter this data on the
design worksheet found in Appendix B.
Determine the fluid gradient, ΔTf. The fluid gradient will depend on fluid type
and temperature. For applications not involving temperature-sensitive fluids, the
following values may be used for simplicity.
ΔTf = 10°F (6K) for fluids similar to water
ΔTf = 30°F (16K) for fluids similar to warm light oils
ΔTf = 100°F (56K) for fluids similar to warm heavy oils
Calculate the tank wall gradient, ΔTw. The gradient depends on wall thickness,
t (inches), and material conductivity, k.
ΔTw = QA x t/k
Contact the tank manufacturer to determine the type and temperature capability
of the tank material. The maximum temperature for polypropylene and FRP is
typically 220°F (104°C). Other plastics, like PVC and polyethylene, have much lower
temperature capabilities and are more suitable for use with Raychem self-regulating
heating cables.
The maximum material temperature for FRP is approximately 220°F. Therefore, the
application is compatible with the tank material.
Primary
thermostat
bulb
WARNING: Fire hazard Table 7 Accessory Selection for Tank Pad Heaters
To prevent fire or shock, Raychem Description Catalog number
brand specified components must
be used. Do not substitute parts or Components
use vinyl electrical tape. Installation kit RHS-INSTALLATION-KIT
Labels ETL
Raychem RHS tank heaters have integrated, resettable thermostats that provide
over-temperature protection in the event of a primary thermostat failure. The RHS
integrated thermostat must not be used as the primary means of temperature
control.
For more details regarding the many options in control devices see Control and
Monitoring design guide (H56889).
The Tank Tracing Design and Product Selection section presented a general
approach to selecting a heat-tracing system for a tank or vessel. The tank heat loss
can be calculated by using the graphs and equations on the following pages. The
approach for the calculation is based on those in the TraceCalc Pro design software.
The overall heat loss (Qt) of an insulated tank can be expressed as:
Qt = Qv + Qs + Qa
where:
Qv = Heat loss through the insulated body of the tank
Qs = Heat loss through the tank support mechanism (slab, legs, saddle, or
other base support)
Qa = Heat loss through accessories such as manholes, handholds, ladders, or
handrails
To calculate the tank’s overall heat loss (Qt), follow these six steps:
1 Calculate the surface area of the tank.
2 Calculate the Qv (heat loss through the insulated body of the tank).
3 Calculate the Qs (heat loss through the base support).
4 Calculate the Qa (heat loss through the accessories).
5 Calculate the Qt (overall heat loss).
6 Calculate the final-design heat loss.
The heat-loss rates for insulated tank bodies (see Table 9 and Graph 1) are based on
the following IEEE 515 provisions:
• Fiberglass insulation
• Tank located outdoors
• No insulating airspace between the tank surface and insulation
The tank body heat loss rates in Table 9 and Graph 1 assume a tank that is
completely full and insulated with a minimum of one inch of fiberglass. However,
Table 10 provides factors for adjusting the tank body heat loss for insulations other
than fiberglass.
H D
(Abody) = πDH
• Calculate the surface area of one or both ends:
(Aend) = πD2/4 or (Aend) = (πD2/4) x 2
• Add the results.
Table 8 below provides both the end and body areas of cylindrical tanks 6 to 20 feet in
diameter and 8 to 25 feet high.
D Abody = π (D+d) S
2
=
π (D+d) (D+d)2
+ H2
H
2 4
S
πD2
Atop =
4
πd2
d Abottom =
4
Fig. 14 Truncated cone surface areas
30
10
3" (76 mm)
4" (102 mm)
5
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
10000
9000
D = 50 ft (15 m)
8000
7000 D = 40 ft (12 m)
6000
Heat Loss (W)
D = 30 ft (9 m)
5000
4000
D = 20 ft (6 m)
3000
2000
D = 10 ft (3 m)
1000
D = 5 ft (1.5 m)
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
600
500 D = 10 ft (3 m)
and up
400
Heat Loss (W)
300
200
D = 5 ft (1.5 m)
100
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
1600
D = 20 ft (6 m)
1400
1200
D =15 ft (4.6 m)
1000
Heat Loss (W)
D = 10 ft (3 m)
800
600
D = 5 ft (1.5 m)
400
200
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
10000
D = 20 ft (6 m)
9000
8000
D = 15 ft (4.6 m)
7000
6000
Heat Loss (W)
5000 D = 10 ft (3 m)
4000
3000
D = 5 ft (1.5 m)
2000
1000
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
Manholes
Select the heat loss for a manhole from Table 15 or Graph 6. The heat loss is
based on a 2-foot diameter cover and a 1-foot tall base. The base and cover are
uninsulated.
3500
3000
2500
Heat Loss (W)
2000
1500
1000
500
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
600
500
400
Heat Loss (W)
300
200
100
0
50 100 150 200 250 300
(10) (38) (66) (93) (121) (149)
∆T °F (°C)
NORTH AMERICA Europe, Middle East, Africa Asia Pacific Latin America
Tel: +1.800.545.6258 Tel: +32.16.213.511 Tel: +86.21.2412.1688 Tel: +1.713.868.4800
Fax: +1.800.527.5703 Fax: +32.16.213.603 Fax: +86.21.5426.2937 Fax: +1.713.868.2333
Tel: +1.650.216.1526 thermal.info@pentair.com cn.thermal.info@pentair.com thermal.info@pentair.com
Fax: +1.650.474.7711
thermal.info@pentair.com
Pentair is owned by Pentair or its global affiliates. All other trademarks are the property of their respective owners. Pentair reserves the right to
change specifications without prior notice.
© 2001-2016 Pentair.