Electrical temperature measurement

Tubeskin temperature
measurements®

Temperature Specialists

About usAlexander Wiegand,
Chairman and CEO, WIKA

Over the past 60 years, WIKA Alexander Wiegand SE & Co.
KG has been a renowned partner and competent specialist
for any task in the field of pressure, temperature and levelmeasurement. On the basis of a steadily growing efficiency,
innovative technologies are applied when developing new
products and system solutions. The readiness to face all
challenges of the market have been the key factors for WIKA
to achieve a leading position in the global market.
Within the WIKA group 7,300 employees are dedicatedto maintaining and improving technology. Within oursales organisation you will find more than 500 skilled andexperienced employees to talk to.

2More than 250 engineers and technicians are continually
searching to provide solutions for innovative products, improved materials and more economical production methods.
In close cooperation with recognised universities, institutes
and industrial companies solutions for specific applications
are developed.

Contents
Tubeskin temperature measurement
applications

4

Product solutions

8

Product selection guide

12

WIKA/Gayesco services for tubeskintemperature measurements

13

Application questionnaire

14

WIKA product lines

15

WIKA - GAYESCOYour engineered product solution for tubeskintemperature measurements
WIKA/Gayesco have been among the world leaders in therefinery and petrochemical industry for more than 50 years.
The WIKA Group has further expanded by acquiring Gayesco
International Inc. This strengthens the market position of thegroup in the field of electrical temperature measurement andon-site services.
Together there are well over 120,000 tubeskinsensors globally supplied by WIKA and Gayesco.

Thus we are more than simply a reliable supplier of highquality measuring instruments: As a competent partner wedevelop products and solutions with you that are specificallytailored to your requirements. WIKA’s high level of performance is characterised by a comprehensive and competent
service and a reliable global presence. We are pleased to becommitted to your success:yesterday, tomorrow and in the future.

3

Tubeskin temperature
measurement applications
Furnace sections
Direct radiation section
The direct radiation section is typically where the radiationfrom the flame heats the tubes. The tubes can be vertical or
horizontal, arranged along the refractory wall, in the middle
or arranged in cells. The tubes are typically 300 - 450 mm(12 - 18") apart inside the furnace. In the illustration on theright, the process tubes are arranged horizontally and theburners are located in the middle of the furnace.
Convection heat section
The convection heat section is located above the direct
radiation section. In this area the heat is not as intense andthe tubes are typically not subjected to direct flame. Herethe tubes are typically 150 - 230 mm (6 - 9") apart inside thefurnace, which sometimes makes it difficult to attach tubeskinthermocouples. Typically tubeskin thermocouples are only
installed on the bottom row (shock tubes).

Direct radiation section

Furnace types
Crude oil
Crude furnaces heat crude oil for processing in a crudedistillation unit. The crude oil composition can vary widelywith type. Crude furnaces are operated under steady state
conditions.
VacuumVacuum furnaces heat crude oil bottoms for further
processing in the vacuum distillation unit. Crude furnaces areoperated under steady state conditions, but coke formation
can be an issue with this furnace type.
Coker
The coker furnace heats heavy oil cuts high in petroleum
residues and asphaltenes for processing in the coke drum.
Premature coke formation in the tubes can be a problem aswell as frequent movement of the furnace during temperature
variations and decoking.
Catalytic reforming
The catalytic reformer furnace heats naphtha range oilfor processing in the reforming reactors. These multi-cellfurnaces are hot and often have three-dimensional processtube movement that can be problematic.

4

Steam reformers/Primary reformers
The SMR furnace is a reaction furnace (catalyst filled tubes)
that creates syngas for hydrogen, ammonia, or methanol
production. These primary reformers are very hot furnaces
that are generally steady state but have large tube movement
parameters.
Hydroprocessing
Hydroprocessing furnaces heat feedstock so that it
can be treated (hydrotreaters) or cracked and treated(hydrocrackers). Hydroprocessing furnaces are generally
steady state with coking potential depending on the type ofmaterial it is processing. Typical hydroprocessing units may
handle just about all oil cuts.
Fluid catalytic cracking
FCC furnaces heat up gas oil for processing in the FCC riser,
and are generally steady state furnaces.
Petroleum residues/Heavy oil processing
Heavy oil furnaces heat up heavy oil for processing inasphalt, ROSE, and other heavy oil processing units.

Purpose of tubeskin temperature measurements
The purpose of tubeskin temperature measurements is todetermine tube life and trending, and to provide safeguards
within a system.
By relying on accurate tubeskin thermocouples clients
can safeguard heater operations at their facilities. This canincrease tube life in furnaces and increase production.
Accuracy Provide accurate data to determine tube life assessment

Durability

 Withstand harsh firebox environment for prolonged periods

Sensitivity

 Detect overheating early on from coke formations
 Allow for accurate adjustment of furnace firing

Safety device

and should last the minimum of one turnaround cycle

 Monitor temperatures and alert in cases where highEase of installation
 Secure weld attachment to the tube wall to fit any tube
size
 Fast installation to meet tight maintenance scheduleduring a shutdown Quick replacement during a shutdown

 Monitor the maximum allowable temperature limits

temperature is reducing the remnant life of the tubeof the tube

Coke formation

5

Tubeskin temperature measurement
applications
Design
WIKA uses trained specialists to customise the temperature
measuring points to the application. These specialists
utilise best practices derived from scientific properties tooptimise the life and accuracy of the thermocouple. They
make suggestions to optimise the system for temperature,
movement, and burner firing.
Some design considerations that can help determine
measuring points for the specific application in order tochoose the best suitable product:

















Material compatibility with furnace tube
Heat transfer (radiation, convection, conduction)
Junction (grounded, ungrounded)
Thickness of the mineral-insulated cable (flexibility vs.
durability)
Expansion loops (location and design)
Flame impingement
Furnace exit design options
Burner fuel (flue gas composition)
Welding procedure (TIG, stick, temperature monitoring)
Mounting (location, orientation)
Operating vs. design temperatures
Bending radiusPath to furnace wall
Weld clips (location and routing)Connection head (material, location, approvals)
Furnace design (burner locations)

Expansion coils exiting the furnace
6

Proper routing with clips

Proper installation
A correct installation is essential to an efficient tubeskinthermocouple system. WIKA/Gayesco services have createdinstallation animations to help those clients who want toinstall the product themselves. WIKA/Gayesco services also
provide installation support up to and including full turnkey
installations for those clients who want to be sure that thesystems are installed properly.
Today, many major refiners, process licensors and furnace
manufacturers rely on WIKA/Gayesco services to provide
tubeskin thermocouple systems for them. Can we design asystem for you?

Trained specialist installing sensor

Internal view of furnace7

Product solutions
V-Pad™
The V-Pad™ design includes a machined v-shaped blockthat is welded to the mineral-insulated cable.
Features of the V-Pad™ include: Material compatibility for various service conditions
 Compaction of the mineral insulation inside of the

V-Pad™ protects the measuring point from radianttemperature influences.
 No special machining of the v-shaped block is required
to match any tube profile.
 The thermocouple is welded into the base of the V-Pad™
for maximum accuracy and fast response.
 The engineered v-shaped block allows a full penetration
weld between the junction and tube surface, eliminating
potential air gaps and substantial measurement
inaccuracies.

Application criteria
 Designed for critical mid-wall temperature measurements
 Designed for use with crude oil, vacuum & coker stylefurnace applications

 Early coke detection to optimise operations and increase

production

 Ease of installation to minimise downtime during

turnaround Suitable for any tube size due to v-shape, reducing spareparts inventory

 Grounded junction
 Longitudinal mounting onto tube

“V-Pad™ is the most accurate thermocouple by far for
all process heaters; it also can detect the onset (beginning) of coking events because of its small footprint.
This has been proven in field tests, as well as fromplant experience.”Frank Liu, former Shell Global Solutions monitoring technology leader

8Refracto-Pad™
The Refracto-Pad™ design utilises a Weld-Pad thermocouple and heat shield.
Features of the Refracto-Pad™ include:Strong welded connection to the process tube
Patented heat shield with a special insulating moulded part
Shield and sensor profile designed to match tube curvature.
Shield protects the sensor cable and allows for quick
routing out of the radiant heat, increasing sensor life.

Application criteria
 Designed for high heat flux or difficult applications,

including flame impingement

 In harsh environments these sensors ensure reliable

readings due to their patented shielded design.

 Grounded or ungrounded junction
 Radial or longitudinal mounting onto tube“... Chevron regards type “A” (Refracto-Pad™) as thebest answer to furnace tubeskin measurement ….”“ Page 3; “Tubeskin Thermocouples”
James G Seebold, Staff Engineer, Chevron Corporation,
in Chemical Engineering Progress, 1985

9

Product solutions
Xtracto-Pad™
The Xtracto-Pad™ design utilises a Weld-Pad attached to a
guide channel and heat shield.
Features of the Xtracto-Pad™ include all of the RefractoPad™ plus:
 Removable thermocouple design allows the thermo-

couple to be replaced without any additional grinding
or welding. It also allows for the weldable parts to be
attached without the presence of the sensor. The WeldPad/guide channel, heat shield and clips can be put on by
the manufacturer of the heater/boiler or even by the tube
manufacturer in the case of special furnace tubes.
 Special features to improve the reliability of the reading
accuracy

Application criteria
 Designed for high heat flux or difficult applications,

up to and including flame impingement

 Weldable parts can be sent to the furnace/tube






manufacturer for initial installation. This is particularly
helpful for special tubes, including spun cast tubesof unique alloy
The Xtracto-Pad™ ensures reliable readings due to its
patented shielded design.
Designed for use with catalytic reformers, steam
methane/naphtha reformers and reaction furnaces
Grounded or ungrounded junction
Radial or longitudinal mounting onto tube

“This design (Xtracto-Pad™) has been adopted,... as a standard for all high chrome furnaces tubes
which require elaborate pre and post-weld heat
treating ...”“High Performance Skin Point Thermocouples - A Chronic Problem Solved”, Larry
M. Braun, Senior Control Systems Engineer, Saudi Aramco 1996 Control System
Technical Exchange Conference, Dhahran, Saudi Arabia, 1996

10

Weld-Pad
The Weld-Pad design utilises a weld-on sheet that is weldedto the furnace tube.
Features of the Weld-Pad include: Designed for low-temperature applications whereaccuracy is not crucial

 Used for tracking trending temperatures
 Low-cost alternative

Application criteriaGrounded or ungrounded junction
Used when flame impingement is not a concern
Ease of installation
Small size

11

Product selection guideSelecting a suitable tubeskin thermocouple can be adaunting task. There are numerous variables that candetermine one sensor style over another.
WIKA’s application specialists can review your applicationand provide custom-designed solutions to fit your needs.
Below is a reference chart for sensor styles for specificapplications.
For an in-depth product review and consultation pleasecontact a WIKA representative for more information.

V-Pad™

Refracto-Pad™

Xtracto-Pad™

Weld-Pad

Accuracy - Mid wall

+++++

++++

+++

+

Accuracy - Surface

++++

+++++

+++++

+

Ease of installation

+++++

++++

++++

+++++

Durability (sensor life)

+++

++++

+++++

+

Replaceability

--

--

+++++

--

Low-temperatureapplications(below 900°F)

+++++

++++

+++

++

High-temperatureapplications

+++

+++

+++++

+

Early coke detection

+++++

+++

++

+

Applications with direct
flame impingement

+++

+++++

+++++

+

Small size

+++++

++

++

+++++

Legend:+Suitable

++

Fair

+++

Good

++++

Very good+++++

Excellent--

Not suitable

12

WIKA/Gayesco services for tubeskin temperature measurements
With WIKA/Gayesco services you can be sure that you havestart-to-finish support. From initial on-site consultation to
installation we have a custom-designed solution for you.

On-site installation crew

Installation

Welding services

WIKA/Gayesco services can provide all manpower, training
and tools required for successful installation of our temperature measurement products. All crew members are familiar
with the handling of these products and have completed
extensive training programmes in working refining and petrochemical plant environments.

All site welders employed by WIKA/Gayesco services are
qualified to ASME Section IX. Installation of our furnace
tubeskin thermocouple assemblies is one of WIKA/Gayesco’s
field service specialties. Since the service life of theseassemblies is dependent upon proper installation, manyclients have turned to us for assistance in this area.

Installation supervision

Field repair

On-site supervision is available to ensure the proper
handling and installation of temperature measurement
systems. Many clients have asked for WIKA/Gayesco
services involvement from the initial shut down planningstage to the final loop check.

WIKA/Gayesco services can assist in repairing or modifying
temperature measuring instruments in the field. Typical fieldwork includes soldering, welding, splicing and bending.

Further information at www.wika.com

13

Application questionnaire
The data provided enables WIKA application specialists toassist you in specifying your thermocouple system. This datais entered in a corporate global application database fortubeskin temperature measurements, enabling the selectionof suitable instruments and their continuous improvement.

Tubeskin thermocouple application questionnaire
Company:

Name:Contact:

Customer details:

Phone:

Fax:

E-mail:Furnace Boiler 

Tube surface 

Vertical 

Horizontal 

Address:
Type of application:
Unit type and location:
Fuel source:
Tube size:
Tube material:
Location of tubes:

Radiation 

Convection 

Condition of tubes:

Used in service 

New installation 

Temperatures:

Ambient:

Process:

Inside vessel:

Inside tubes:

V-Pad ™ 

Xtracto-Pad™ 

Refracto-Pad ™ 

Weld-Pad Type of sensor:
Tag numbers:
Location on tubes:
Sensor pad material:
Material of MI cable:

MI cable diameter:

MI cable length(including expansion loops):
Thermocouple calibration:
Style of attachment to wall:

N.U.N. 

Style of attachment to tube:

Welded 

Gas seal Strap material:
FEA calculations required:

Additional notes:

14

Consult engineering

Compression fitting Strapped Spring loaded 

Piston 

WIKA product lines

The WIKA programme covers the following product lines for various fields of application.

Electronic pressure measurement

Electrical temperature measurement

WIKA offers a complete range of electronic pressure measuring instruments: pressure sensors, pressure switches,pressure transmitters and process transmitters for themeasurement of gauge, absolute and differential pressure.
Our pressure measuring instruments are available in themeasuring ranges 0 ... 0.6 mbar to 0 ... 15,000 bar. These
instruments come supplied with standardised current or
voltage output signals also intrinsically safe per ATEX or withflameproof enclosure, interfaces and protocols for various
field buses. Whether ceramic thick film, metal thin film or
piezo-resistive, WIKA is the leading manufacturer worldwide
that develops and produces the full range of today’s leading
sensor technologies.

Our range of products includes thermocouples, resistancethermometers also with on-site display, temperature switches
as well as analogue and digital temperature transmitters for
all industrial applications, covering measuring ranges from-200 ... +1,600 °C.

Mechatronic pressure measurement
As a result of the almost unlimited options for different
combinations of mechanical and electrical connections, an
extraordinary range of instrument variants is possible.
Various digital and analogue output signals are also available
for these measuring instruments. For our measuring
instruments we use latest sensors, tested in automotive
applications millions of times over. They work without
any kind of mechanical contact, consequently they are
wear-resistant, and there's absolutely no influence on themechanics.

Mechanical pressure measurement
Indicating instruments for gauge, absolute and differential
pressure with Bourdon tube, diaphragm or capsule pressure element have been tested millions of times over. These
instruments cover scale ranges from 0 … 0.5 mbar to0 … 7,000 bar and accuracies of up to 0.1 %.

Diaphragm seals
WIKA diaphragm seals, fitted with pressure gauges, pressuretransducers, pressure transmitters etc., are recognised andvalued internationally for the most difficult of measuring tasks.
The measuring instruments can thus be used at extreme
temperatures -90 ... +400 °C and aggressive, corrosive,
heterogeneous, abrasive, highly viscous or toxic media. The
optimal diaphragm seal designs, materials and filling media
are available for each application.

For all product lines product reviews are available.

Mechatronic temperature measurement
As a result of the integration of switch contacts and output
signals into our mechanical temperature measuring instruments, we can offer a wide variety of combined instruments.
With switch contacts the pointer position triggers a changeover. Electrical output signals are realised via an additional,
independent sensor circuit resistance thermometer orthermocouple.

Mechanical temperature measurement
The mechanical temperature measuring instruments work on
the bimetal, expansion or gas actuation principle and coverscale ranges from -200 ... +700 °C. All thermometers are
suited for operation in a thermowell as required.

Level measurement
WIKA has a comprehensive range of level measuring
instruments available for temperatures up to 450 °C, specificgravity from 400 kg/m³ and pressure ranges up to 420 bar. This
includes standard instruments and customised products.

Primary flow measurement
Orifice plates, meter runs, flow nozzles, Venturi tubes andpitot tubes are part of our portfolio of primary flow elements
and restriction orifices. The wide range of our products is able
to cover the majority of industrial applications. Customised
solutions can be developed to meet your special needs.

Calibration technology
WIKA offers a broad product spectrum of calibration
instruments for the physical measured values of pressure
and temperature, and for electrical measured values. A
multitude of specific patents ensure unmatched performance
characteristics with many of our calibration instruments.
The range of services comprises the calibration of pressure
and temperature measuring instruments in our accredited
DKD/DAkkS calibration laboratories and a mobile service tocalibrate your instruments on site.

15

WIKA worldwide
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WIKA Messgerätevertrieb
Ursula Wiegand GmbH & Co. KG
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WIKA Alexander Wiegand SE & Co. KG
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14079468 04/ 2023 EN

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