Core classification dimensions:
First. With certification vs. without certification:
With certification: refers to pipe fittings manufactured in accordance with specific, recognized international or national standards (such as API, ASME/ANSI, ISO, DIN, BS, etc.), and have passed the corresponding quality assurance system certification (such as API Q1, ISO 9001) and/or product certification (such as API Monogram, CE-PED). These pipe fittings are usually used in critical, high-pressure, high-temperature, hazardous media or regulatory mandatory applications (such as oil and gas, chemicals, power, ships, pharmaceuticals). Certification ensures that materials, dimensions, tolerances, manufacturing processes, testing (such as non-destructive testing, pressure testing) and traceability meet strict standards.
Without certification: refers to pipe fittings produced in accordance with general industrial standards or the manufacturer’s own standards, and may not have undergone strict third-party certification or conformity assessment. This type of pipe fittings is usually used in general industrial or civil applications with low pressure, low temperature, non-critical, non-hazardous media (such as general water and gas pipelines, non-pressure structures, temporary facilities). The cost is usually lower, but the consistency of quality and reliability may not be as good as that of certified products, and the traceability is also poor.
Second. American Standard Thread vs British Standard Thread:
American Standard Thread: Mainly refers to NPT and NPTF threads that follow the ASME B1.20.1 standard.
NPT: American standard taper pipe thread. The taper is 1:16. It needs to be sealed with sealants (such as raw tape, thread sealant). It is extremely widely used.
NPTF: American standard dry seal taper pipe thread. It also has a 1:16 taper, but the thread tooth shape is designed to be tighter (tooth top and tooth bottom interference). In theory, it can be sealed without the help of sealants (dry seal). It is often used in places where sealants are not allowed or as an additional sealing guarantee. In practical applications, NPTF also often uses sealants.
British standard thread: Mainly refers to threads that follow BS EN ISO 228-1 (G) and BS EN 10226-1 (R/Rp) standards (old standards are BS 2779, BS 21).
G (BSPP): British standard parallel pipe thread. The thread is cylindrical. The sealing is mainly achieved by the gasket (such as O-ring, flat gasket, composite gasket) between the planes of the connection ports. The thread itself does not provide sealing, but only serves to tighten the connection. The common code G is followed by the size (such as G1/2″).
BSPT: British standard tapered pipe thread. The taper is 1:16. Sealant (such as raw tape, thread sealant) is required to achieve sealing. External thread code R (such as R1/2″), internal thread code Rc (cone pipe internal thread) or Rp (parallel pipe internal thread – Note: Rp internal thread matched with R taper external thread is parallel, but relies on cone/flat fit and sealant to seal).
Important difference: BSPP (G) is a parallel thread, sealed by gasket; BSPT (R) is a tapered thread, sealed by thread + sealant.
Learn more:NPT Thread Fitting;BSPT Thread Fittings.
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Third. Common pipe fitting types and their thread applications:
Elbow:
- Purpose: Change the direction of the pipe (90°, 45°, 180°, etc.).
- Thread type: Both ends can be NPT/NPTF (American standard) or G/R (British standard). It can also be threaded at one end and welded or flanged at the other end.
- Certification: Certification is required for high pressure and critical occasions (API, ASME), and certification is not required for general low pressure occasions.
Tee:
- Purpose: Divide or merge fluids (equal diameter tees, reducing tees).
- Thread type: All three ports can be NPT/NPTF (American Standard) or G/R (British Standard), or a combination (such as two side ports with threads and main port welded). Reducing tees have different thread sizes at the ports.
- Certification: Same as elbow.
Cross:
- Purpose: To separate two vertical branches from the main pipe (less common).
- Thread type: Similar to tee, with four ports.
- Certification: Same as elbow.
Pipe fitting/straight connector:
- Purpose: To connect two pipes in the same straight line.
- Thread type: Both ends are internally threaded NPTF/NPT (American Standard) or G (BSPP) / Rc (BSPT). Used to connect two pipes or fittings with external threads.
- Certification: Commonly used, certification is required for high pressure critical occasions.
- Reducing joint:
- Purpose: Connect two pipes of different diameters.
- Thread type: The internal thread size at both ends is different, which can be a combination of NPT/NPTF (American Standard) or G/R (British Standard) (such as 1″ x 1/2″). There are also external thread x internal thread (Bushings) or external thread x external thread (Couplings).
- Certification: Same as straight connector.
Pipe cap:
- Purpose: Close the end of the pipe.
- Thread type: Internal thread NPTF/NPT (American Standard) or G/Rc (British Standard), used to screw on the pipe end or fitting with external thread.
- Certification: Certification is required for important occasions.
Pipe plug/thread plug:
- Purpose: Close the opening on the pipe fittings (such as tees, valves, instrument interfaces).
- Thread type: External thread NPT/NPTF (American Standard) or G/R (British Standard), used to screw into ports with internal threads.
- Certification: Certification is required for important occasions.
Union:
- Purpose: Provides a detachable connection point for easy installation and maintenance.
- Thread type: Both ends are usually internal threads NPT/NPTF (American Standard) or G/Rc (British Standard), connected in the middle by a sealing gasket with a cone or flat surface (matching washer) and a lock nut. Its own connection method is independent of the pipe thread standard, but its port thread still needs to comply with the American Standard or British Standard.
- Certification: Removable connection points usually require better quality and are more reliable with certification.