1. SCOPE ……………………………………………………….
2. REFERENCES ……………………………………………………….
3. DEFINITIONS ……………………………………………………….
4. TEMPERATURE INSTRUMENTS …………………………..
4.1 General……………………………………………………….
4.2 Thermocouples ……………………………………………………….
4.3 Resistance Temperature Detectors (RTD) …………………………..
4.4 Thermistors ……………………………………………………….
4.5 Temperature Transmitters…………………………..
4.6 Filled Thermal System …………………………..
4.7 Bimetallic Thermometers …………………………..
4.8 Thermowells ……………………………………………………….
5.
INSPECTION AND TESTING ……………………………………………………….
6. REVISION HISTORY ……………………………………………………….
1. Scope
This standard establishes minimum requirements for the use of temperature instrumentation
systems in process plants.
2. References
Reference is made in this standard to the following documents. The latest issues, amendments
and supplements to these documents shall apply unless otherwise indicated.
SABIC Engineering Standards (SES)
R01-E01 Field Instrumentation Design Criteria
E11-C01 General Instrument Installation Criteria
X05-E01 Process Control Cabling and Wiring
X05-S01 Process Control Cable Specification
International Electrotechnical Commission (IEC)
IEC 60751 Industrial Platinum Resistance Thermometer Sensors
Instrumentation, Systems and Automation Society (ISA)
MC 96.1 Thermocouple Tolerances
American Society of Mechanical Engineer (ASME)
B1.20.1 Pipe Threads, General Purpose (inch)
B16.5 Pressure and Temperature Ratings for Pipe and Flanged Fittings
PTC W19.3 Performance Test Code-Temperature Measurement
B40.3 Bimetallic Actuated Thermometers
Process Industry Practices (PIP)
PCITE200 RTD/Thermocouple Installation Details
PCFTE100 Thermowell Fabrication Details
3. Definitions
For the purpose of understanding this standard, the following definitions apply:
Bimetallic Thermometers. The Bimetallic Thermometer consists of temperature sensitive
element housed in a stainless steel sheath and connected to indicator enclosed in an integral
case. Temperature changes will cause the free end of the helix to rotate, actuating the indicator.
Compensation. Provision of a supplemental device, circuit, or special materials to counteract
known sources of error.
Filled Thermal System. The filled thermal system consists of a metal thermometer or
temperature-sensing bulb connected by means of a metal capillary to a receiving element
located in the instrument. The receiving element may be a bellows, diaphragm, capsule, simple
Bourdon, spiral, or helix.
Natural Frequency. The frequency of free (not forced) oscillations of the sensing element of a
fully assembled transducer.
Protecting Tube. A protecting tube is designed to enclose a temperature sensing device and
protect it from the deleterious effects of the environment. It may provide for attachment to a
connection head but is not primarily designed for pressure-tight attachment to a vessel.
Reference Junction. That thermocouple junction which is at a known or reference temperature.
The reference junction is physically that point at which the thermocouple or thermocouple
extension wires are connected to a device or where the thermocouple is connected to a pair of
lead wire, usually copper.
Sensing Element. That part of the transducer which responds directly to the value of measured
variable.
Temperature coefficient. The rate of change of some physical property-electrical resistance,
for instance-with temperature; the coefficient may be constant or nearly constant.
Thermistors. A temperature transducer constructed from semiconductor material and for which
the temperature is converted into a resistance, usually with negative slope and high nonlinearity.
Thermocouple. A Temperature measuring transducer that develops an electric voltage when
heated because of the combined thermoelectric effect due to dissimilar composition between
two electrically connected conductors (usually wires) and to temperature difference between the
connection (measuring junction) and the other end of the conductors (reference junction).
Thermowell. A thermowell is a pressure-tight receptacle adapted to receive a temperature
sensing element and provided with external threads or other means for pressure-tight
attachment to a vessel.
Wake Frequency. When a thermowell is inserted into a flowing liquid or gas, circular flow
pattern is created downstream of the thermowell. These flow patterns are called Von Karman
vortices. These vortices break away periodically, known as Vortex Shedding and causes a
regular change in the force on the thermowell. This regular change or frequency of vortex
shedding is called wake frequency.
4. Temperature Instruments
4.1 General
4.1.1 For general design, guidelines and specification refer to SES-R01-E01.
4.1.2 For installation of temperature instruments refer to SES-E11-C01.
4.1.3 Dual thermocouples or RTDs shall be installed to provide a spare element for a single
measurement. Second element of dual element assembly shall not be used to provide
separate signals. However, due to application constraint, single element assembly can be
used with SABIC approval.
4.1.4 The thermocouple and RTD cable shall conform to SES-X05-S01.
4.1.5 Refer to SES-X05-E01 for wiring details.
4.1.6 Sheath material of thermocouples and RTDs shall be 316 stainless steel, as a minimum,
unless process conditions require different material.
4.1.7 Thermocouples and RTDs shall be mineral insulated with minimum 6 mm stem diameter.
However, due to application constraint, other stem diameters can be used with SABIC
approval.
4.1.8 Thermocouples and RTDs assembly shall be in accordance with PIP PCITE200
4.1.9 Temperature sensors selection shall be in accordance with PIP PCETE001.
4.1.10 For control and safety applications temperature sensor with transmitter shall be used.
4.1.11 Thermowell shall be purchased along with its temperature element to assure proper fit, with
the exception of test thermowell.
4.2 Thermocouples
4.2.1 The design and fabrication of thermocouples and extension wires shall conform to ISA
MC96.1.
4.2.2 Type T or K thermocouple shall be used, and ranges shall be as per ISA MC96.1.
4.2.3 Other types of thermocouples can be used with SABIC approval.
4.2.4 All thermocouples used in plants shall be ungrounded unless otherwise specified.
4.2.5 Multipoint thermocouple assembly shall require SABIC approval. Design features shall
include secondary seal to ensure safe containment and mechanism to prevent junction box
pressurization on the loss of primary seal.
4.3 Resistance Temperature Detectors (RTD)
4.3.1 RTDs shall be 100 Ohms at 0 deg C, platinum and comply with IEC 60751, having a
temperature coefficient of 0.00385 Ohm per deg C. Use of other types of RTDs shall be with
SABIC approval.
4.3.2 RTDs shall be of three lead wire design. Four lead wire RTDs are acceptable only for
special applications with SABIC approval.
4.3.3 Temperature range of RTDs shall be within – 184 deg C to 538 deg C.
4.4 Thermistors
4.4.1 The use of thermistors shall be limited to alarm applications and shall require SABIC
approval.
4.4.2 Only, thermistors with negative temperature coefficient shall be used.
4.4.3 Thermistors have low mass and limited heat dissipation capabilities. Therefore, the
manufacturer’s data shall be used in calculations of heat dissipation to ensure self heating
does not occur.
4.4.4 Thermistors shall not be used for wide span measurement due to their nonlinear resistance
versus temperature relationship.
4.5 Temperature Transmitters
4.5.1 The transmitter shall provide linearized output for all applicable sensors.
4.5.2 The transmitter shall have electrical isolation of minimum 500 V RMS between the input and
output signals to allow the use of grounded thermocouples.
4.5.3 Head mounted temperature transmitters are acceptable provided the mounting location is
free from vibration and temperature extremes.
4.5.4 Transmitters shall provide thermocouple reference junction ambient temperature
compensation.
4.5.5 Temperature transmitter shall be programmable and be able to accept RTD or
thermocouple of any type and range.
4.5.6 Multiplexers shall be used only for non critical measurement at the approval of SABIC.
4.6 Filled Thermal System
4.6.1 Filled systems are not recommended for temperature indicator, transmitters or switches,
and shall be used only with SABIC approval.
4.6.2 Bulbs shall have bendable extension union connected with a pressure tight gland.
4.6.3 Filled type thermometers shall be over range protected.
4.6.4 Vapor and mercury filled systems are not acceptable.
4.7 Bimetallic Thermometers
4.7.1 Thermometer minimum accuracy class should be +/- 1 percent of span as per ASME B40.3
Grade A.
4.7.2 Thermometer dial size shall range from 100 to 150 mm, with stem length from 2.5 to 24
inches. Dials shall be non-reflective, white, with black graduations, numerals and pointer.
4.7.3 Outside diameter of protecting tube shall be minimum 6 mm.
4.7.4 Thermometers case shall be made of stainless steel.
4.7.5 Thermometers head shall be hexagonal or wrench flat.
4.7.6 Thermometer dials shall be swivel type.
4.7.7 Thermometers shall have provision of zero adjustment and mechanical stopper for the
pointer.
4.7.8 Bimetallic thermometer shall be used for local indications only.
4.7.9 Back connected or bottom connected models shall be specified depending on applications.
4.7.10 When subjected to vibration, silicone oil filled thermometer shall be used.
4.8 Thermowells
4.8.1 Thermowells shall be provided for all temperature sensing elements except for surface or
skin temperature measurements, and temperature measurements in low pressure ducts,
where the element does not need protection from harmful atmospheres, corrosive fluids, or
mechanical damage. Warning tags shall be installed wherever temperature elements are
installed without thermowells.
4.8.2 Thermowell design as defined herein shall not be applicable to those included in the scope
of furnace and heaters design. The design of such thermowells shall be done by equipment
vendor.
4.8.3 Thermowell material shall be 316 stainless steel, as a minimum, unless process conditions
require different material.
4.8.4 Flanged thermowells shall have flanges and weld filler of the same material as specified for
the thermowell, and shall have full penetration welds.
4.8.5 The construction of standard thermowells shall be in accordance with Thermowell Types
drawings of PIP PCFTE100.
4.8.6 Thermowell process connection shall comply with SES-R01-E01 connection size and type
requirements.
4.8.7 Test thermowells shall be furnished with threaded 316 stainless steel plugs and chains.
4.8.8 Threaded thermowells shall undergo hydrostatic test to an internal pressure of 17250 kPa
(2500 psig) or 1.5 times the maximum operating pressure, whichever is higher.
4.8.9 Flanged thermowells shall undergo hydrostatic test externally as per ASME B16.5.
4.8.10 Thermowells shall be suitable for stresses due to stream velocity conditions. The wake
frequency, commonly referred as Strouhal or the Von Karman frequency, shall not exceed
66 percent of the thermowell natural frequency, in accordance with ASME PTC 19.3. This
calculation shall be performed by the vendor.
4.8.11 The thermowell immersion length ‘U’ shall be selected such that the tip falls in the middle
third of the pipe diameter, considering maximum velocity rating of thermowell.
4.8.12 When harmful vibrations caused by Von Karman vortices are anticipated, the immersion
length shall be shortened so that the thermowell is protected from resonance and damage.
4.8.13 Thermowells shall be stamped with the tag number of its corresponding temperature
element.
4.8.14 In erosive and corrosive services, thermowell shall have heavier wall and tip thickness.
5. Inspection and Testing
Vendor shall submit following test certificates and test reports of temperature instrument for
purchaser’s review:
a. Material certificate
b. Dimensional drawings
c. Wake frequency calculation for thermowell
d. Hydrostatic test report for thermowell
e. Calibration reports, except for thermowells