Threaded Thermowells

Threaded thermowells are precision-engineered protective fittings designed to shield temperature sensors — such as thermocouples and RTDs — from direct contact with process media. By isolating the sensing element from the process fluid, they allow instruments to be installed, removed, or replaced without interrupting operations or breaching process containment.

Material Grades

Threaded thermowells are available in three stainless steel grades to suit a wide range of process environments:

• SS 304 — General-purpose austenitic stainless steel offering good corrosion resistance for standard industrial applications.
• SS 316 — Enhanced molybdenum content provides superior resistance to chlorides and aggressive chemical environments.
• SS 316L — Low-carbon variant of 316, preferred for welded assemblies and applications requiring maximum intergranular corrosion resistance.

Thread Types and Process Connection

The threaded process connection allows direct installation into tapped bosses, couplings, or pipe fittings without the need for flanges or additional hardware. Two internationally recognised thread standards are supported:

• NPT (National Pipe Taper) — Widely used in North American and international process industries; provides a pressure-tight seal through thread interference.
• BSP (British Standard Pipe) — Common in European and Middle Eastern installations; available in parallel (BSPP) and taper (BSPT) forms.

Insertion Lengths

Insertion lengths are available from 50 mm to 500 mm, enabling correct sensor positioning at the centre of flow in pipes of varying diameters. Custom lengths can be specified to meet project-specific requirements. Proper insertion length selection is critical to measurement accuracy and thermowell mechanical integrity.

Shank Designs

Two shank profiles are offered to balance mechanical strength, wake frequency response, and heat transfer characteristics:

• Tapered shank — Reduces diameter towards the tip, improving wake frequency performance and response time while maintaining root strength.
• Straight shank — Uniform diameter along the full insertion length; suited to lower-velocity applications and where maximum bore diameter is required for the sensor.

Pressure and Temperature Ratings

Threaded thermowells are rated for high-temperature and high-pressure service, making them suitable for demanding process conditions. Ratings depend on material grade, thread size, wall thickness, and insertion length. Typical operating ranges cover temperatures up to 600 °C and pressures up to 250 bar, subject to design verification per applicable standards such as ASME PTC 19.3 TW.

Typical Applications

Threaded thermowells are widely used across industrial process plants wherever reliable temperature measurement is required:

• Oil and gas pipelines and process headers
• Pressure vessels, reactors, and storage tanks
• Chemical and petrochemical processing units
• Water and steam distribution systems
• Power generation and utility plants
• Food, beverage, and pharmaceutical processing