Comprehensive Guide to Pipe Fittings

Pipe fittings refer to general‑purpose components within pipeline systems for connection, control, flow redirection, branching, sealing and support.

Product Introduction

Pipe fittings are components used to join individual pipes to build a complete pipeline system. According to processing technology, pipe fittings fall into butt‑welded fittings, threaded fittings and flange fittings.

‑ Fittings for pipe connection: flexible fittings, pipe clamps, tubing fittings

‑ Fittings for flow direction change & branching: elbows, bent pipes, tees, crosses

‑ Fittings for pipe diameter transition: reducers, branch supports, reinforcing pipes

‑ Fittings for pipeline fixation: snap‑ring fittings, drag‑hook fittings, lifting‑ring fittings, bracket fittings

Product Classification

Pipe fittings can be categorized by function, connection type, material and manufacturing method.

Classified by Function

1. Pipe‑connecting fittings: flanges, unions, pipe clamps, sleeves, hose clamps

2. Direction‑changing fittings: elbows, bent pipes

3. Diameter‑changing fittings: reducers (reducing pipes), reducing elbows, branch pipe platforms, reinforcing pipes

4. Branch‑outlet fittings: tees, crosses

5. Sealing fittings: gaskets, PTFE tape, hemp packing, flange blind plates, pipe plugs, blind plates, heads, welding plugs

6. Pipeline‑fixing fittings: snap rings, drag hooks, lifting rings, brackets, pipe clamps

Classified by Connection Type

1. Welded pipe fittings

2. Threaded pipe fittings

3. Compression sleeve fittings

4. Clamp‑on fittings

5. Socket‑joint fittings

6. Adhesive‑bonded fittings

7. Hot‑melt fittings

8. Curved double‑fusion fittings

9. Rubber‑ring sealed fittings

Classified by Material

1. Cast‑steel pipe fittings

2. Cast‑iron pipe fittings

3. Stainless‑steel pipe fittings

4. Plastic pipe fittings

5. PVC pipe fittings

6. Rubber pipe fittings

7. Graphite pipe fittings

8. Forged‑steel pipe fittings

9. PPR pipe fittings

10. Alloy pipe fittings

11. PE pipe fittings

12. ABS pipe fittings

Chemical Composition

For chemical‑composition verification of pipe fittings, please refer to ASTM / ASME / GB material specifications for each material grade.

Common international test standards for chemical analysis include GB223, JIS G1211‑1215, BS 1837, BS Manual 19, GOST 22536, etc.

Standard Systems for Pipe Flanges

Two major internationally‑recognized pipe‑flange standard systems exist:

1. European system: represented by German DIN standards (including former Soviet‑Union specifications)

2. American system: represented by ASME/ANSI B16.5 and ASME B16.47

Japanese JIS flange standards are also available but are mostly applied for on‑site utility works within petrochemical plants and have limited global influence.

The European and American flange systems are non‑interchangeable.

ISO 7005‑1 (published 1992 by ISO) is a hybrid standard combining specifications from both European and American flange series.

Further Classification of Pipe Fittings

1. By Material Grade

‑ Carbon steel: ASTM/ASME A234 WPB, WPC

‑ Alloy steel: ASTM/ASME A234 WP1‑WP12‑WP11‑WP22‑WP5‑WP91‑WP911, 15Mo3, 15CrMoV, 35CrMoV

‑ Stainless steel:

ASTM/ASME A403 WP 304‑304L‑304H‑304LN‑304N

ASTM/ASME A403 WP 316‑316L‑316H‑316LN‑316N‑316Ti

ASTM/ASME A403 WP 321‑321H, ASTM/ASME A403 WP 347‑347H

‑ Low‑temperature steel: ASTM/ASME A402 WPL3‑WPL6

‑ High‑strength steel: ASTM/ASME A860 WPHY 42‑46‑52‑60‑65‑70

‑ Other materials: cast steel, alloy steel, stainless steel, copper, aluminum alloy, plastic, PVC, PPR, RFPP (reinforced polypropylene), etc.

2. By Production Method

Extruded, pressed, forged, cast.

3. By Manufacturing Standard

Chinese national standard (GB), electric‑power standard (DL), ship‑building standard (CB), petrochemical standard (SH/HG), water‑works standard, American standard, German standard, Japanese standard, Russian standard, etc.

4. By Radius of Curvature (Elbows)

‑ Long‑radius elbow: Curvature radius R = 1.5 × pipe outer diameter D (R=1.5D)

‑ Short‑radius elbow: Curvature radius R = 1.0 × pipe outer diameter D (R=1.0D)

D = elbow nominal outer diameter; R = radius of curvature.

5. By Pressure Schedule

Seventeen schedule designations consistent with US pipe standards:

Sch5s, Sch10s, Sch10, Sch20, Sch30, Sch40s, STD, Sch40, Sch60, Sch80s, XS, Sch80, SCH100, Sch120, Sch140, Sch160, XXS.

STD and XS are the most widely used.

Relevant Standards

Chinese National Standards (GB / GB/T)

‑ GB/T 10752‑1995, Marine steel pipe butt‑welded joints

‑ GB/T 8803‑2001, Injection‑molded rigid polyvinyl chloride (PVC‑U), chlorinated polyvinyl chloride (PVC‑C), ABS and ASA fittings — Hot‑oven test

‑ GB/T 8802‑2001, Thermoplastic pipes and fittings — Determination of Vicat softening temperature

‑ GB/T 18251‑2000, Determination of pigment or carbon‑black dispersion in polyolefin pipes, fittings and compounds

‑ GB/T 18474‑2001, Test method for cross‑linking degree of cross‑linked polyethylene (PE‑X) pipes and fittings

‑ GB/T 18475‑2001, Classification and nomenclature of materials for thermoplastic pressure pipes and fittings — General service factors

‑ GB/T 18742.3‑2002, Polypropylene piping systems for hot‑and‑cold water — Part 3: Fittings

‑ GB/T 18991‑2003, Thermoplastic pipes and fittings for hot‑and‑cold‑water systems

‑ GB/T 18993.3‑2003, Chlorinated polyvinyl chloride (PVC‑C) piping systems for hot‑and‑cold water — Part 3: Fittings

‑ GB/T 18998.3‑2003, Chlorinated polyvinyl chloride (PVC‑C) industrial piping systems — Part 3: Fittings

‑ GB/T 19228.3‑2003, Rubber O‑ring seals for stainless‑steel compression fittings

‑ GB/T 19278‑2003, Thermoplastic pipes, fittings and valves — General terms and definitions

‑ GB/T 19473.3‑2004, Polybutene (PB) hot‑and‑cold‑water piping systems — Part 3: Fittings

‑ GB/T 12459‑2005, Steel butt‑welded seamless fittings

‑ GB/T 19712‑2005, Plastic pipes and fittings — PE saddle‑bypass impact‑test method

‑ GB 15558.2‑2005, Underground PE gas‑pipeline systems — Part 2: Fittings

‑ GB/T 13663.2‑2005, PE water‑supply piping systems — Part 2: Fittings

‑ GB/T 19806‑2005, Plastic pipes and fittings — Peel test for PE electro‑fusion assemblies

‑ GB/T 19807‑2005, Plastic pipes and fittings — Preparation of composite test specimens for PE pipes and electro‑fusion fittings

‑ GB/T 19808‑2005, Plastic pipes and fittings — Tensile‑peel test for PE electro‑fusion fittings DN ≥ 90 mm

‑ GB/T 19809‑2005, Plastic pipes and fittings — Preparation of PE hot‑melt‑butt‑weld joint specimens

‑ GB/T 19810‑2005, PE pipes and fittings — Tensile‑strength and failure‑mode test for hot‑melt‑butt joints

‑ GB/T 13401‑2005, Steel plate butt‑welded pipe fittings

‑ GB/T 19993‑2005, Hot‑and‑cold‑water thermoplastic piping systems — Thermal‑cycling test for pipe‑fitting assemblies

‑ GB/T 5836.2‑2006, PVC‑U fittings for building drainage

‑ GB/T 15819‑2006, Test method and technical requirements for environmental‑stress‑cracking sensitivity of irrigation PE pipes with inserted fittings

‑ GB/T 20201‑2006, Mechanical connection fittings for irrigation PE pressure pipes

‑ GB/T 20207.2‑2006, ABS pressure piping systems — Part 2: Fittings

‑ GB/T 20674.2‑2006, Plastic pipes and fittings — PE fusion equipment — Part 2: Electro‑fusion connections

‑ GB/T 20674.1‑2006, Plastic pipes and fittings — PE fusion equipment — Part 1: Hot‑melt butt‑welding

‑ GB/T 8801‑2007, Drop‑impact test for PVC‑U pipe fittings

‑ GB/T 21300‑2007, Determination of opacity for plastic pipes and fittings

‑ GB/T 21409‑2008, General rules for inspection, installation and operation of glass process pipes and fittings

‑ GB/T 21408‑2008, Glass process pipes and fittings — Interchangeability for DN 15‑150 mm components

‑ GB/T 14383‑2008, Forged socket‑weld and threaded pipe fittings

‑ GB/T 13295‑2008, Ductile‑iron pipes, fittings and accessories for water‑gas transmission pipelines

‑ GB/T 6567.3‑2008, Technical drawings — Graphical symbols for piping systems — Fitting symbols

‑ GB/T 22051‑2008, Cross‑linked‑polyethylene (PE‑X) pipes with sliding‑clamp cold‑expansion fittings

‑ GB/T 6567.5‑2008, Technical drawings — Axonometric graphical symbols for piping, fittings and valves

‑ GB/T 11618.1‑2008, Copper tube joints — Part 1: Brazed fittings

‑ GB/T 12772‑2008, Flexible‑joint cast‑iron drainage pipes, fittings and accessories

‑ GB/T 3420‑2008, Grey‑cast‑iron pipe fittings

‑ GB/T 11618.2‑2008, Copper tube joints — Part 2: Compression‑type fittings

‑ GB/T 23241‑2009, Basic parameters and technical conditions for irrigation plastic pipes and fittings

‑ GB/T 23682‑2009, Refrigeration‑system and heat‑pump hose fittings, isolators and expansion joints — Requirements, design and installation

‑ GB/T 24452‑2009, Indoor sewage‑wastewater PVC‑C pipes and fittings (high‑low temperature service)

‑ GB/T 17457‑2009, Ductile‑iron pipes and fittings with cement‑mortar lining

‑ GB/T 24596‑2009, Polyurethane‑coated ductile‑iron pipes and fittings

‑ GB/T 24672‑2009, Metal thin‑wall pipes and fittings for sprinkler irrigation

‑ GB/T 5135.19‑2010, Automatic sprinkler systems — Part 19: Plastic pipes and fittings

‑ GB/T 26002‑2010, Stainless‑steel corrugated hoses and fittings for gas transmission

‑ GB/T 26120‑2010, Low‑pressure stainless‑steel threaded pipe fittings

‑ GB/T 26081‑2010, Ductile‑iron sewage pipes, fittings and accessories

‑ GB 26255.2‑2010, Mechanical fittings for PE gas‑piping systems — Part 2: Steel‑plastic transition fittings for DN > 63 mm

‑ GB 26255.1‑2010, Mechanical fittings for PE gas‑piping systems — Part 1: Steel‑plastic transition fittings for DN ≤ 63 mm

‑ GB/T 26500‑2011, General technical requirements for fluoroplastic‑lined steel pipes and fittings

‑ GB/T 19228.2‑2011, Stainless‑steel compression‑fitting assemblies — Part 2: Thin‑wall stainless‑steel connecting pipes

‑ GB/T 19228.1‑2011, Stainless‑steel compression‑fitting assemblies — Part 1: Compression‑fitting components

‑ GB/T 27684‑2011, Titanium and titanium‑alloy seamless & welded pipe fittings

‑ GB/T 27891‑2011, Carbon‑steel compression‑type pipe fittings

Chinese Industry Standards

1. GB/T 12459‑2005, Steel butt‑welded seamless fittings

2. GB/T 13401‑2005, Steel‑plate butt‑welded pipe fittings

3. DL/T 695‑1999, Steel butt‑welded pipe fittings for power stations

4. SH 3408, Steel butt‑welded seamless pipe fittings

5. SH 3409, Steel‑plate butt‑welded pipe fittings

6. SH 3410, Forged‑steel socket‑weld pipe fittings

7. HGJ514‑87, Seamless butt‑welded carbon‑steel & low‑alloy‑steel pipe fittings

8. CJ/T 321‑2010, Aluminum‑alloy‑lined plastic composite pipes and fittings

American Pipe‑Fitting Standards

‑ ASME/ANSI B16.9, Factory‑made wrought butt‑welded steel pipe fittings

‑ ASME/ANSI B16.11, Socket‑welded and threaded forged fittings

‑ ASME/ANSI B16.28, Steel butt‑welded short‑radius elbows and return bends

‑ ASME B16.5, Pipe flanges and flange fittings

‑ MSS SP‑43, Forged stainless‑steel butt‑welded pipe fittings

‑ MSS SP‑83, Socket‑weld and threaded unions

‑ MSS SP‑97, Integrally‑reinforced socket‑end, threaded‑end and butt‑weld‑end outlets

‑ ASME B16.3‑1998, Malleable‑iron threaded pipe fittings

Characteristics and Applications

Pipe fittings are widely used in petrochemical, power generation, water supply & drainage, HVAC, shipbuilding, marine engineering, fire protection, metallurgy and new‑energy projects.