Piping Materials : Threaded Fittings

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Threaded fittings are used in non critical applications and when service fluid is at ambient temperatures such was instrument air, plant air, cooling water, potable water etc. As they do not require welding, they are used at places where welding is not permitted. Though ASME B16.11 provides dimensions for 1/8″ to 4″ size threaded fittings, normally in process plant, 1/2″ to 1-1/2″ fittings are used.

Threaded Piping Fittings

Threaded Piping Fittings

Ratings for Threaded Fittings are Class 2000, 3000, 6000. Choice of Class depends on thickness schedule of pipe, as given in ASME B16.11.

  1. Class 2000 for Sch80 and XS,
  2. Class 3000:Sch 160, 6000:XXS

Size range as per ASME B16.11 is 1/8″ to 4″.

Dimensional Standards

ASME B16.11 : Forged Fittings, Socket Welding and Threaded.

MSS-SP-83 : Class 3000 Steel Pipe Unions, Socket-Welding and Threaded

Available Fittings

Threaded 90 Degree Elbow
Used for 90 degree turn of piping in threaded piping systems. Available size range is from 1/8" to 4" as per ASME B16.11.

Dimensions Table

Threaded 45 Degree Elbow
Used for 45 degree change in direction of piping. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Cap
Used to close end of pipe. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Straight and Reducing Tee
Used for 90 degree branch connection of same or reducing size. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Cross
These are sparingly used to reduce inventory. Two tees used instead. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Full Coupling
Used to connect one piece of pipe to another in straight direction. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Half Coupling
Used for connecting small bore threaded branch to large bore welded pipe. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Reducing Coupling
These fittings are used as reducer in threaded piping networks. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Hex Plug
Used to close one end of threaded fitting such as Tee or Elbow etc. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Close Nipple
OD is as per standard pipe dimensions. Length is as per project requirement. Made from standard pipe piece.
Both End Threaded Nipple
Made from standard pipe piece as per project requirement. Used to connect two threaded fittings near to each other. OD is as per standard pipe dimensions.
POE TOE Nipple
Used to connect socket weld small bore piping to threaded small bore piping. OD is as per standard pipe dimensions. Length is as per project requirement.
Threaded Pipe to Tube Connector
Typical use is to connect instrumentation tubes to Air Pipes. Also used for Analyser Tubing.
Threaded Hexagon Bushing
These are used as reducers in threaded piping network by connecting smaller size pipe to bigger size female threaded fitting. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Unions
Unions permits easy installation, removal or replacement of lengths of pipe, valves or vessels in screwed piping systems. To remove a valve it must have at least one adjacent union and to remove piping from a vessel with threaded connections, each outlet from the vessel should have one union between valve and vessel. Inside Union, ground faced joints are preferred, although other facings are available.
Threaded Reducing Insert
These fittings are used to connect two female threaded fittings of different sizes to each other.
Square Head Plug
Used to close one end of female threaded fitting for future expansion. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Round Head Plug
Used to close vent and drain holes of valves, steam traps etc. Also to close end of female threaded pipe fittings. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Threaded Flush Bushing
Used to connect reduced size pipe to larger size female threaded fitting. Available size range is from 1/8″ to 4″ as per ASME B16.11.

Dimensions Table

Advantages of Threaded Fittings

  1. Threaded joints can be easily made from pipe and fittings on site.
  2. They minimize fire hazard when installing in areas where flammable gases and liquids are present.

Disadvantages of Threaded Fittings

  1. Use of threaded joints is not permitted by ANSI B31.1 if sever erosion, crevice corrosion, shock or vibration is anticipated, nor at temperatures over 925 F.
  2. Chances of leakage are high with threaded joints.
  3. Seal welding may be required in more risky situations.
  4. For threaded joints, strength of pipe is reduced as forming the screw thread reduces the wall thickness.

Materials of Construction

These fittings are forged fittings. So Materials of Construction are as follows.

  1.  A105  : Standard Specification for Carbon Steel Forgings for Piping Applications.
  2. A181 : Standard Specification for Carbon Steel Forgings, for General-Purpose Piping.
  3. A182 : Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service.
  4. A350 : Standard Specification for Carbon and Low-Alloy Steel Forgings, Requiring Notch Toughness Testing for Piping Components.

Sample Piping Material Specification

Elements : 45 Degree elbow, 90 Degree elbow, Equal Tee, Reducing Tee, Caps, Full Coupling, Reducing Coupling

  1. Material : CS : ASTM A105. Galvanised, NIC, HIC as per spec.
  2. Material : SS : ASTM A182 F304L
  3. Threaded : 2000:Sch80 and XS, 3000:Sch 160, 6000:XXS
  4. Ends : Threaded Female Ends,
  5. Dim Standard : ASME B16.11

Elements : Pipe to Tubing Adapter

  1. Material : CS:ASTM A105,
  2. Class : NA,
  3. Ends : Female threaded end / Compression twin ferrule, Dim Standard : Manufacturer.

Elements : Hex Head Bushing

  1. Material : CS : ASTM A105,
  2. Ends : Threaded Male / Threaded Female Ends.,
  3. Standard : ASME B16.11

Elements : Concentric Swage, Eccentric Swage

  1. Material : CS : Made from seamless pipe ASTM A234 Gr. WPB
  2. Material : SS : Made from seamless pipe ASTM A403 Gr. WP304LS
  3. Ends : Threaded Both Ends, Standard : BS3799

Element : Round Head Plug

  1. Material : CS : ASTM A105,
  2. Ends : Threaded Male Ends,
  3. Standard : ASME B16.11

Element : Union

  1. Material : CS : ASTM A105,
  2. Class : 3000,
  3. Ends : Compression Twin Ferrule both Ends,
  4. Standard : Manufacturer Standard

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