Basic Thermowell Structure – Shank Construction
Thermowell Tip Profile
- Tapered: The outside diameter progressively reduces along the length of the immersion. This is utilized for various high-speed applications.
- Flat Tip: One end of this is having a flattened surface. This one is utilized for low-pressure applications or in places where the flow characteristics that are around the body aren’t that significant.
- Domed Tip: This type of protective cover has a hemispherical tip at the thermowell at one of the ends. This one is utilized in various high-pressure applications or in places where the flow characteristics, which are around it, are quite significant.
- Spherical Tip: For this, a special drill with 118ºC tip angle is utilized for thermowell’s production. The end is spherical i.e. in the shape of a ball, for achieving wall thickness as uniform as possible.
Basic Thermowell Structure – Shank Construction
- Q-Dimension: This happens to be the shank’s thickest segment on the hotter side of flange or process connection. This depends on the size of the bore & that of the process connection.
- Bore size: This is Thermowell’s inner diameter. This can also be referred to as the diameter of the cylindrical cavity inside the thermowell or protective tube. The standardized drilling dimensions are 6.5mm and 8.5mm.
- Immersion U-Length: Thermowell’s length or that of the protecting tube, which is under the flange, the mounting threads, the bushing, etcetera; extending into the area of the process. This length, ‘U,’ is actually measured from the process connection bottom to that of the Thermowell’s tip.
- Lagging Extension T-Length: Additionally to the standardized head lengths, the trailing extension length is required to allow access to the end of the trailing extension and allow the probe to reach through insulation/walls.
- Inside Mounting Thread: Thermowell’s inside thread shields to secure the junction temperature device & nipple extension for the assembly of a Thermowell.
Flange Face Types
- Raised-Face or RF: This is the most commonly used flange type, and this one can be easily identified. This is called an RF or the raised surface as the sealing surfaces are raised above the surface of the bolt circle.
- Ring-Type Joint or RTJ: Its flanges have grooves, which are cut into the surface that seal with steel rings.
- Flat Face or FF: This one has a sealing surface that is in the similar plane as the surface of the bolt circle.
Thermowell Welding
Welding is actually the process in which 2 metals are joined by heating them to a suitable temperature. This can be made with or without pressure, and with or without any filling. The 2 main types are as under:
- Full Penetration – This particular type of weld provides a fully-welded interface between 2 parts & is usually the sturdiest joint.
- Partial Penetration – This particular type of weld consists of an interface that is partially welded with a filler metal placed on the surface of the 2 metals.
WPS & PQR
WPS stands for Welding-Procedure-Specification. It is actually a document, which tends to describe the process of welding and how it should be done in production. These are advisable for all sorts of welding operations as well as the many application codes & standards tend to make them kind of mandatory. WPQR or PQR is shortened to Procedure-Qualification-Record. This is something that supports the WPS. This is actually a test-weld that has been made & tested (quite rigorously) for ensuring a good weld with the procedure.
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