Technical Information
TI245T/02/en
71105488

Thermowell for temperature sensors
omnigrad TW251
Thermowell for general applications
Integrated compression fitting
Threaded or weld-in process connection

TW 251 is a tube well fitted with an integrated compression fitting, suitable fordifferent industrial applications including
hygienic applications.
It is normally fitted onto pipes and vessels
or tanks where attachment to the process
can be threaded or welded.
Its construction, capable of housingprobes with a diameter of 6 mm, allows
for the combination with TST 42, TST 425,
TST 310, TEC 420 and TSC 310 temperature sensors.
Available in different executions (straight,reduced or tapered), it has a an immersion length that can be chosen according
to the demands of the process.

Features and Benefits• The compression fitting allows for thereplacement of the faulty probes without having to suspend the process
underway• Sleeves for the compression fitting
available in PTFE or SS 316• Different process connections can beselected as standard within the sales
structure:– threaded (G ½", G ¼", NPT ½", ...)– weld-in (cylindrical, spheric)• The 3.1.B material certificate (according to standard EN 10204), is selectable directly from the sale structure ofthe productomnigrad TW 251

Areas of application
Suitable for numerous applications including the food industries, it is generally used in all systems
that require a protection well for temperature sensors with a 6 mm diameter.
Especially suitable when the operator does not want to interrupt the process for replacement of adamaged sensor, or to check for its correct operation.

Function and system design
TW 251 is a thermowell made from a tube with an outer diameter of 9 mm. The inner diameter ofthe well allows for the combination of an insert with a 6 mm diameter in the straight execution,
while the tapered and reduced executions can house an insert with a 3 mm tip. For further details
on the type of execution and process connections, refer to the chapter “System components”.
25251/2” GAS

25

25

30

321/2” NPT
Ø 25

Ø 25
ILIL3Fig. 1:IL

Ø ID
Ø93

Ø ID
Ø9IL3

Ø ID
Ø93

Ø ID
Ø9TW251X_G_dd_13_xx_01

Equipment architecture

Overall dimensions of the TW 251

Material

Wetted parts in SS 316L/1.4404.

WeightFrom 0.5 to 1.5 Kg for standard options.

Performance
Operating conditions

Maximum process pressure• 5 Mpa (50 bar)• 3.3 Mpa (33 bar)• 2.4 Mpa (24 bar)at 20°Cat 250°C
at 400°C

Maximum process temperature• well stem

600°C

Maximum temperature of the compression fitting• compression fitting with PTFE sleeve• compression fitting with SS 316 sleeve

180°C
400°C

Maximum flow velocity
The maximum velocity of the process medium supported by the well is reduced when the immersion length exposed to the stream increases.

2Endress+Hauseromnigrad TW 251

Installation

Fig. 2:

TW251X_h_id_13_xx_02

TW251X_h_id_13_xx_01

Omnigrad TW 251 may be installed onto tubes or tanks through the use of threaded connections
G ½", G ¼", ½" NTP, or using the cylindrical or spheric connections to be welded; different processconnections from the ones indicated may be provided upon request.
During installation it is necessary to consider the immersion length, as an incorrect evaluation may
alter the accuracy of the sensor; for this reason the immersion should possibly be at least 80 mm.
In the case of the installation in tubes with a reduced diameter, the axis line of the duct should bereached and if possible it should be slightly exceeded from the tip of the well (see Fig. 2).
Installation of the well inclined and with its sensitive part counterposed to the normal flow of theprocess, may be a valid alternative to the most commonly used perpendicular one (see Fig. 2).
Special attention should be paid in the case of the installation of processes with two-phase flows,since they may cause fluctuations in the detected temperature values.
In the case of hygienic applications it is better to avoid empty spaces in the area below the process connection. Furthermore, for connections to be welded the user must choose suitable welding materials, using a bead ray of welding exceeding 3 mm, avoiding the formation of pits, folds,crevices.
The measuring insert has to be assembled to the thermowell, in the way that the tip of the probemust be in contact with the base of the pipe; after that it has to be fixed in this position by meansof the compression fitting.
A thermoconductive paste may be used till 200°C, in order to optimise the heat transfer between
thermowell and insert.

Installation in tubes (on the left); alternatives to installation (on the right)

System components

TW251X_G_DD_13_en_02

Thermowell

The immersion length is available in the most commonly useddimensions; alternatively, dimensions that are different fromstandard ones may be chosen upon request by the client within
the range of values indicated in the sales structure (refer to thelast page of this document).
The finishing of all the parts in contact with the process medium
is available with a minimum value of Ra < 0.4 microns; at thismoment no values below this figure have turned out to be advantageous, especially in the food industries. TW 251 is available invarious executions (see Fig. 3): straight, reduced (by using awelded cap of a diameter of 5.3 mm - L=20 mm to close the endof the well) or tapered (with a gradual reduction of the well stemthat allows for the outer diameter to be reduced from 9 mm to 6.6mm). In the case of a reduced execution a minimum immersion
length of 45 mm is requested, while for the tapered version it mustbe of at least 85 mm; in both cases the well can be used in combination with a probe with a 3 mm tip (TST 42 with a reduced end).
Fig. 3:Different executions for the tip of TW 251

Endress+Hauser

3omnigrad TW 251

Compression fitting

The compression fitting is an integral part of the well. Available in different alternatives, with aPTFE (equivalent to Teflon®) or stainless steel sleeve, it allows for fixing of the sensor in the correct
position. The version with the PTFE sleeve is ideal for the repeated replacement of the probe, while
the steel sleeve is used for permanent fixing of a sensor as the pressure ring blocks it into position.

Process connection

The threaded connections (G ½", G ¼", ½" NTP) as well as the connections to be welded (cylindrical or spheric) can be selected directly from the sale structure. Upon request different connections can be chosen.
connection 1/2” NPT

CIL251_G_gd_13_xx_02

cylindrical connection to be welded

SPH251_G_gd_13_xx_02

spheric connection to be welded

NPT251_G_gd_13_xx_02

GAS251_G_gd_13_xx_02

connection G 1/2”

Certificates & approvalsMaterial certification

The 3.1.B material certificate (in compliance with the standard EN 10204) can be selected directlyfrom the sale structure, in its various versions. The base certificate includes a simplified declaration, including enclosures of the documents related to the materials used in the construction ofeach well. Besides the previous certificates, a “labelled” version also exists which guarantees
traceability of the certificate thanks to the registration of the serial numbers of each single well.

Additional information
Maintenance

The Omnigrad TW 251 well does not require any specific maintenance. For the version with thesleeve in PTFE, it should be controlled periodically and possibly substituted, when the mechanicalsealing is no longer efficient.

Delivery time

For small quantities (approx. 10 units) and standard options, delivery time is from 10 to 20 workingdays.

4Endress+Hauser

omnigrad TW 251

Ordering information
Product structure

TW251

Process connection
G2
G4N2WC
WS
YY

Process connection G 1/2”
Process connection G 1/4”
Process connection 1/2” NPT
Cylindrical connection to be welded: D25xL30 mm
Spheric connection to be welded D25xL30 mm
Special option

Sleeve material(for the compression fitting)

BPY

Sleeve in SS 316
Sleeve in PTFE (Teflon®)
Special option

Immersion length(50-1000 mm)

ACEGHXY

50 mm immersion length L
100 mm immersion length L
150 mm immersion length L
200 mm immersion length L
300 mm immersion length Lmm immersion length L to specify
mm immersion length L to specify

Diameter of the protecting tube D, material and finishing of wetted parts
56799 mm, SS 316L/1.4404, Ra<=1.2 µm
9 mm, SS 316L/1.4404, Ra<=0.8 µm9 mm, SS 316L/1.4404, Ra<=0.4 µm
Special version

Type of tip
SRTY

Straight tip
Reduced (with step), only for L>=45 mm(it can be used only in combination with a TST42 with a 3 mm tip)
Tapered, only for L>=85 mm(it can be used only in combination with a TST42 with a 3 mm tip)
Special version

Certificates0BGD
H
TW251-

Certificate not required
3.1.B EN10204, standard for wetted parts
3.1.B EN10204, labelled for wetted parts
3.1.B EN10204, standard + roughness
3.1.B EN10204, labelled + roughness
complete order codeAccessories❑ 60011599 KIT of 10 sleeves in SS 316 Ø 6 mm
❑ 60011600 KIT di 10 sleeves in PTFE Ø 6 mm
❑ 60007126 Thermoconductive paste

Endress+Hauser

5Supplementary documentation❑ General technical information on TST❑ Technical information on the thermometric sensor TST42❑ Technical information on the thermometric sensor TST425❑ Technical information on the thermometric sensor TST310❑ Technical information on the thermometric sensor TEC420

TI 088T/02/en
TI 184T/02/en
TI 113T/02/en
TI 085T/02/en
TI 076T/02/en

Subject to modification

Endress+Hauser
Gmbh+Co.
Instruments International
P.O. Box 2222
D-79574 Weil am Rhein
Germany
Tel. (07621) 975-02
Tx 773926
Fax (07621) 975 345
http://www.endress.com
info@ii.endress.com

TI245T/02/en/11.02
71105488
FM+SGML 6.0