July 1999
Process Industry Practices
PIP PCCTE001
Temperature Measurement Criteria
PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES
In an effort to minimize the cost of process industry facilities, this Practice has
been prepared from the technical requirements in the existing standards of major
industrial users, contractors, or standards organizations. By harmonizing these technical
requirements into a single set of Practices, administrative, application, and engineering
costs to both the purchaser and the manufacturer should be reduced. While this Practice
is expected to incorporate the majority of requirements of most users, individual
applications may involve requirements that will be appended to and take precedence over
this Practice. Determinations concerning fitness for purpose and particular matters or
application of the Practice to particular project or engineering situations should not be
made solely on information contained in these materials. The use of trade names from
time to time should not be viewed as an expression of preference but rather recognized as
normal usage in the trade. Other brands having the same specifications are equally
correct and may be substituted for those named. All practices or guidelines are intended
to be consistent with applicable laws and regulations including OSHA requirements. To
the extent these practices or guidelines should conflict with OSHA or other applicable
laws or regulations, such laws or regulations must be followed. Consult an appropriate
professional before applying or acting on any material contained in or suggested by the
Practice.
© Process Industry Practices (PIP), Construction Industry Institute, The
University of Texas at Austin, 3208 Red River Street, Suite 300, Austin,
Texas 78705. PIP member companies may copy this practice for their internal
use.
Not printed with State funds
July 1999
Process Industry Practices
Process Control
PIP PCCTE001
Temperature Measurement Criteria
Table of Contents
1. Introduction .................................2
1.1 Purpose ............................................2
1.2 Scope ...............................................2
2. References ..................................2
2.1 Process Industry Practices ................2
2.2 Industry Codes and Standards ..........2
3. Technical Requirements ............3
3.1 Data..................................................3
3.2 Electrical Area Classification.............3
3.3 Shutdown Service.............................3
6. Resistance Temperature
Detectors..................................... 5
7. Temperature Transmitters ......... 6
8. Stand Alone Electronic
Indicators .................................... 6
9. Indicating Thermometers........... 6
10. Filled and Mechanical Thermal
Systems....................................... 7
4. Thermowells................................3
11. Installation Requirements.......... 7
5. Thermocouples ...........................4
Attachment:
PCCTE001 - Temperature Instrument
Installation
Process Industry Practices
Page 1 of 7
PIP PCCTE001
Temperature Measurement Criteria
1.
July 1999
Introduction
1.1
Purpose
The purpose of this Practice is to provide design criteria for the equipment
selection, system design, and installation of temperature instrumentation.
1.2
Scope
This Practice specifies requirements for design and installation of temperature
measurement instrumentation. Installation details are addressed in other Process
Industry Practices (PIP) documents.
2.
References
Applicable requirements in the latest edition (or the edition indicated) of the following
industry standards and references shall be considered an integral part of this Practice.
Short titles will be used herein when appropriate.
2.1
2.2
Process Industry Practices
–
PIP PCETE001 - Temperature Measurement Guidelines
–
PIP PCFTE000 - Temperature Measurement Fabrication Details
–
PIP PCIEL000 - Instrumentation Electrical Installation Details
–
PIP PNF0200 - Vents, Drains, and Instrument Connection Details
Industry Codes and Standards
•
American Society of Mechanical Engineers (ASME)
–
•
American Society for Testing and Materials (ASTM)
–
•
CGA G-4.4 - Industrial Practices for Gaseous Oxygen Transmission and
Distribution Piping Systems
International Electrotechnical Commission (IEC)
–
•
ASTM E230 - Standard Temperature Electromotive Force (EMF) Table
for Standardized Thermocouples
Compressed Gas Association (CGA)
–
•
ASME PTC 19.3 - Performance Test Code - Temperature Measurement
IEC 60751 - Industrial Platinum Resistance Thermometer Sensors
(International Equivalent of Standard DIN 43760)
ISA
–
ISA S20 - Specification Forms for Process Measurement and Control
Instruments, Primary Elements, and Control Valves
ISA S20.10A - Specification Form, Potentiometer Instruments
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Process Industry Practices
PIP PCCTE001
Temperature Measurement Criteria
July 1999
ISA S20.10B - Specification Form, Potentiometer Instruments
(multiple)
ISA S20.11A - Specification Form, Temperature Instruments - Filled
Systems
ISA S20.11B - Specification Form, Temperature Instruments - Filled
Systems (multiple)
ISA S20.12A - Specification Form, Thermocouples & Thermowells
ISA S20.12B - Specification Form, Thermocouples & Thermowells
(multiple)
ISA S20.13A - Specification Form, RTDs & Thermowells
ISA S20.13B - Specification Form, RTDs & Thermowells (multiple)
ISA S20.14A - Specification Form, Industrial Bimetal and Glass
Thermometers
ISA S20.14B - Specification Form, Industrial Bimetal and Glass
Thermometers (multiple)
–
3.
ISA MC96.1 - Temperature Measurement Thermocouples
Technical Requirements
3.1
3.2
Data
3.1.1
A data set shall be provided for each temperature instrument. The data set
can be electronic or hard copy format.
3.1.2
ISA S20.10, ISA S20.11, ISA S20.12, ISA S20.13, and ISA S20.14
Specification Forms define the minimum data set.
Electrical Area Classification
All equipment shall meet the specified electrical area classification.
3.3
Shutdown Service
Temperature elements in shutdown service shall be separate from elements in
control service and installed in separate thermowells.
4.
Thermowells
4.1
Thermowells (TWs) connection type (welded, screwed, or flanged) shall match the
applicable Piping Specification.
4.2
TW material shall be 316 SS unless the process requires other material of
construction.
4.3
Consult a materials specialist for “weld-in” TWs on piping above
650° F.
Process Industry Practices
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PIP PCCTE001
Temperature Measurement Criteria
4.4
July 1999
All temperature sensors shall be installed in TWs.
Exception (1): Skin temperature sensors are not installed in TWs.
Exception (2): Temperature sensors in some services that are not hazardous
may be installed without a TW (e.g., services such as ambient air, motor
windings, bearing temperatures, and electronic equipment cabinets).
Exception (3): Temperature sensors in a process service that normally would
be in a TW but require a faster response than can be achieved with a TW may
be installed without a TW if the following safeguards are met:
•
Each installation is approved by Owner.
•
Warning tags are placed on each installation.
4.5
Consideration shall be given to fluid velocity impact on TWs. Calculations shall
be performed using ASME PTC 19.3 if TWs are installed perpendicular to the
flow and velocities exceed those listed in PIP PCETE001 Attachment 2 for the
wells fabricated to PIP PCFTE000.
4.6
TWs shall be constructed from solid stock unless otherwise approved by owner.
4.7
Standard TW bore sizes for temperature elements shall be 0.26 inch and 0.385
inch.
4.8
TWs installed in oxygen service shall meet the requirements of CGA G-4.4 and the
engineering standards of the oxygen producer. (Refer to Article 4.3, “Velocity,” of
CGA G-4.4 for requirements.)
Comment: Minute particles in gaseous oxygen service (22 to 100% O2 by
volume) may heat up if they impinge at high velocity on obstructions in the
pipe (e.g., TWs, throttle valves, orifice plates, pipe tees, strainers, etc.) Monel
and/or Hastelloy materials of construction may be required depending on the
pressure and temperature of the service.
4.9
5.
Standard TWs shall be of tapered design in accordance with PIP PCFTE001,
PIP PCFTE002, and PIP PCFTE003.
Thermocouples
5.1
Thermocouples (TCs) shall be fabricated with 18 gauge wire minimum, in hard
packed magnesium oxide insulation with 1/4-inch OD 316 SS sheath, epoxypotted extension wire exit from sheath, and grounded hot junction per PIP
PCFTE004.
Comment: Inconel sheath and high temperature insulation is required for
applications above 600o F.
5.2
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TCs shall comply with ISA MC96.1 and ASTM E230 for TC types B, E, J, K, R,
S, and T.
Process Industry Practices
PIP PCCTE001
Temperature Measurement Criteria
July 1999
5.3
Type J shall be used only with owner’s approval.
Comment: Type J TCs contain iron wire which is subject to corrosion in many
locations.
5.4
The sheathed TC hot junction shall be grounded (except for differential, averaging,
or other applications requiring ungrounded).
Exception: Grounded junction TCs will not give accurate measurements when
connected together to measure differential or average temperature. Ungrounded
TCs must be used in these applications. Individual TCs connected to measuring
instruments are preferred.
5.5
The TC metal sheath shall be connected to the ground connection terminal strip in
the TC head via the extension wire shield in the sealed transition piece. Crimped
connections are not acceptable.
5.6
TC heads shall have the following characteristics:
1. Cast aluminum or owner approved alternative
2. Compression type terminal block with brass terminals and an extra terminal
for attaching the extension wire shield connection
(Duplex TCs require six terminals.)
3. Two internally threaded conduit connections
6.
Resistance Temperature Detectors
6.1
Resistance Temperature Detectors (RTDs) shall use a 100 ohm platinum element
(resistance measured at 0° C) wound on a ceramic or glass core, hermetically
sealed and manufactured in accordance with IEC 60751, Class B.
6.2
RTDs shall comply with the IEC 60751 (equivalent to DIN 43760) temperature
coefficient of 0.00385 ohms per ohm per degree Celsius.
6.3
RTDs shall be enclosed in a 1/4-inch OD 316 SS protection sheath, with an epoxy
sealed transition piece and copper lead wire to a weatherproof head. RTDs shall
be fabricated with 18 gauge wire minimum, in hard packed magnesium oxide
insulation.
Comment: Inconel sheath and high temperature insulation is required for
applications above 600o F.
6.4
RTDs shall use insulated nickel or nickel alloy wire from the platinum element to
the epoxy sealed transition piece where the copper wires shall be attached by
welding or soldering. Crimped connections are not acceptable.
6.5
RTDs shall have the 3 lead wire design; 4 wire RTDs are acceptable for special
applications.
6.6
Wire insulation shall be color coded per ISA.
Process Industry Practices
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PIP PCCTE001
Temperature Measurement Criteria
6.7
July 1999
RTD heads shall have the following characteristics:
1. Cast aluminum or owner approved alternative
2. Compression type terminal block with brass terminals with an extra screw
provided for attaching the extension wire shield
(Duplex RTDs require 6 or 8 terminals.)
3. Two internally threaded conduit connections
7.
Temperature Transmitters
7.1
Temperature transmitters shall be smart electronic with an input from a TC or
RTD sensor.
7.2
Electronic temperature transmitters shall have the following characteristics:
1. Accuracy, including the combined effects of linearity, hysteresis and
repeatability, equal to or better than +/-0.25% of the calibrated span
2. Span, TC/RTD input type, etc. shall be configurable.
7.3
Transmitters having a TC input shall also provide:
1. Input/output isolation
2. Cold junction compensation
3. Automatic TC burnout detection with selectable upscale or downscale
failure mode. Transmitter burnout shall be configured.
4.
7.4
Built-in temperature linearization capability for output signal
Transmitters having RTD input shall also provide:
1. Input/output isolation
2. A dedicated screw connection for use in grounding the RTD extension
wiring shield
8.
Stand Alone Electronic Indicators
8.1
Stand alone electronic indicators (indicators that receive a temperature element as
a direct input) shall have the following characteristics:
1. Receive either TC or RTD signals
2. Direct readout in degrees Fahrenheit or degrees Celsius
3. Circuitry that provides a linearized readout
8.2
9.
Instruments with TC input(s) shall incorporate cold junction compensation and
automatic TC burnout detection.
Indicating Thermometers
9.1
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Mercury-filled thermometers are not acceptable.
Process Industry Practices
PIP PCCTE001
Temperature Measurement Criteria
July 1999
9.2
Thermometers shall have a minimum accuracy of plus or minus 1.0% of the scale
span.
9.3
Indicating thermometers shall be designed to install into a TW with a 0.10 inch
clearance between the thermometer stem and the TW inside diameter. The stem
length of thermometers shall be selected to bottom out in the TW in which they are
to be installed.
9.4
Bimetallic thermometers shall have the following characteristics:
1. Single or multiple helix measuring element contained in a dampening fluid
2. Minimum 5-inch diameter dial face with a nonglare white finish and black
or contrasting color markings
3. Stainless steel, every angle weatherproof case with bezel ring
4. 1/4-inch OD protection tube
5. Hexagonal head or wrench flats
6. Industry standard length
7. Display temperature units (°F and/or °C)
10.
11.
Filled and Mechanical Thermal Systems
10.1
Filled thermal element transmitters and controllers are not recommended. Use of
filled thermal systems requires owner’s approval.
10.2
Owner approval is required for the use of any direct actuated (e.g., capillary or
bimetal) temperature switch.
10.3
Use of self-actuated temperature regulators requires owner’s approval.
Installation Requirements
11.1
TWs shall be located a minimum of ten (10) diameters downstream of the mixing
point for liquids.
11.2
TWs shall be located a minimum of 30 diameters downstream of the mixing point
for gases or desuperheaters.
11.3
TWs mounted in horizontal vessels shall have at least an 18-inch insertion length;
however, insertion length shall not exceed 1/2 the vessel diameter.
Exception: Special requirements such as agitated vessels may require shorter
TW installations.
11.4
See PIP PCIEL000 for temperature instrument electrical connections.
11.5
See PIP PNF0200 for TW connections to piping.
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