How To Choose A Threaded Pup Joint?

There are many factors to consider when choosing a threaded pup joint to ensure that it can be connected safely, reliably and leak-free in the pipeline system. The following are the key steps and considerations for selecting a threaded pup joint:

Determine the thread type and standard (the most critical step)

It must match the thread of the component to be connected (pipe, valve, equipment interface) exactly! Common thread types include:

1. NPT (National Pipe Taper)

The American standard taper pipe thread is the most commonly used, relying on the taper of the thread itself and the sealing material (such as raw tape, sealant) to achieve sealing. The nominal diameter is expressed in inches (such as 1/2" NPT, 3/4" NPT).

2. BSPT (British Standard Pipe Taper)

British/European standard taper pipe thread (R series). The function is similar to NPT, but the tooth angle is 55° (NPT is 60°). The two are not compatible. The nominal diameter is also expressed in inches (e.g. 1/2" BSPT).

3. BSPP (British Standard Pipe Parallel)

British/European standard straight pipe thread (G series). The threads are parallel and the seal relies on the gaskets (e.g. O-rings, gaskets) on the end faces. The nominal diameter is expressed in inches (e.g. 1/2" BSPP, G1/2"). Not compatible with BSPT threads.

4. Other types

Such as metric taper threads, dry seal threads, etc., are relatively rare and need to be determined according to specific equipment requirements.

Determine the nominal diameter

It must be consistent with the nominal diameter of the thread of the component to be connected (e.g. 1/2", 3/4", 1", DN15, DN20, etc.).

Note: The nominal diameter of NPT, BSPT, and BSPP refers to the approximate flow diameter of the inner hole, not the actual outer diameter of the thread. For example, the outer diameter of a 1/2" NPT fitting is much larger than 0.5 inches.

Determine the length

1. Standard length

Most threaded pup joints have standard lengths for conventional connections.

2. Special lengths

Extended lengths: For situations where extra space is required (such as installing instruments, crossing gaps) or where a deeper screw-in depth is required.

Shortened lengths: For situations where space is limited.

Determine the material

The material must be compatible with the medium being transported (corrosion-resistant) and meet the system pressure and temperature requirements. Common materials include:

1. Carbon steel

A106, A105, etc. Economical, high strength, suitable for general water, oil, gas and other non-corrosive media.

2. Stainless steel

304, 316, 316L, etc. Excellent corrosion resistance, suitable for corrosive environments such as chemicals, food, medicine, seawater, or situations with high cleanliness requirements. 316/L has better corrosion resistance than 304, especially chloride resistance.

3. Alloy steel

Such as A182 F11, F22, etc. With higher strength and high temperature resistance, it is suitable for high pressure and high temperature systems (such as boiler feed water, steam).

4. Brass

Good corrosion resistance (especially to water), often used in low pressure water systems, instrument connections.

5. Other alloys

Such as Monel, Hastelloy, etc., used in extremely corrosive environments.

Determine the pressure rating and standard

The rated working pressure of the threaded pup joint must be equal to or higher than the design pressure of the pipeline system.

The material and manufacturing standard determine its pressure rating. Common standards:

1. American standard

ASME/ANSI B16.11 (socket welding and threaded forging pipe fittings), pressure ratings are Class 2000, 3000, 6000, etc.

2. European standard

EN 10241 or DIN standard.

3. Others

JIS, GOST, etc.

Consider the end form and sealing method

Both ends of the threaded pup joint are usually the same type and size of thread.

Sealing method

1. Tapered thread (NPT, BSPT)

Sealing is mainly achieved by thread engagement and the sealant (raw tape, thread sealant) filled between the threads. Tightening torque is critical.

2. Straight thread (BSPP)

Sealing is mainly achieved by the gasket (flat gasket, O-ring) compressed by the end face, and the thread itself mainly serves as a connection.

Consider installation space and direction

Make sure the length and shape of the selected short section (straight type is the most common) are suitable for the space limitations of the installation location.

If the space is very narrow, a shorter model may be required or other connection methods may be considered (such as welding short sections plus threaded joints).

Confirm whether the direction of the connection at both ends of the short section meets the requirements.

Special requirements

1. Surface treatment

Such as galvanizing (rust prevention), coating, etc.

2. Special working conditions

Such as low temperature, severe vibration, high purity requirements, etc., may require special designs or materials.

3. Comply with specific industry specifications

Such as API specifications for the oil and gas industry, specifications for the shipbuilding industry, etc.