Piping Materials : Socket Weld Fittings

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Pros

  1. They are easier to use on small-size pipelines and ends of the pipes need not be bevelled since the pipe end slips into the socket of the joint.
  2. With socket welded fittings, there is no danger of the weld protrusion into the pipeline and restricting flow or creating turbulence.
  3. No tack welding is necessary for alignment since joint and the pipe are self-aligning.
  4. It can be used in place of threaded fittings, therefore, reducing the likelihood of leaks, which usually accompany the use of threaded fittings.
  5. It is less expensive and easier to construct than other welded systems. Joints will not leak when properly made.

Cons

  1. With socket weld fittings, there is a possibility of a mismatch inside the fitting where improperly aligned or mated parts may create a recess where corrosion could start.
  2. The 1/16 inch recess in joint for thermal expansion pockets liquid and also can cause corrosion, is case of highly corrosive liquids.
  3. Not used in Hydrogen Service. (All fittings are Buttwelding including small bore for hydrogen service).
  4. Use not permitted by ANSI B31.1 if severe vibration or crevice corrosion is anticipated.

Applications

  1. For lines conveying flammable, toxic or expensive material, where no leakage can be permitted.
  2. For steam: 300 to 600 PSI, and sometimes 150 PSI steam.

Fittings

Available fittings as per B16.11 are

  1. 90 deg. LR Elbow,
  2. 45 deg. LR Elbow,
  3. Caps,
  4. Straight and Reducing Tees,
  5. Straight Cross,
  6. Full Coupling,
  7. Half Coupling,
  8. Reducing Coupling
  9. No Such Fittings : Shot Radius elbows, returns, bends and reducers.

Dimensional Standards

  1. ASME B16.11 : Forged fittings, Socket welding and threaded.
  2. MSS-SP-79 : Socket Welding Reducing Insert
  3. MSS-SP-83 : Steel Pipe Unions, Socket welding and threaded.
  4. MSS-SP-95 : Swaged Nipples and Bull Plug.

90 Deg LR Elbow

Available for size range 1/8″ to 4″ as per ASME B16.11.

45 deg. LR Elbow

Available for size range 1/8″ to 4″ as per ASME B16.11.

Caps

Available for size range 1/8″ to 4″ as per ASME B16.11. They are used for closing dead end of plain end small bore pipe.

Straight and Reducing Tees

Available for size range 1/8″ to 4″ as per ASME B16.11. They are straight as well as reducing.

Straight Cross

Available for size range 1/8″ to 4″ as per ASME B16.11. They are used sparingly, as it is better to use 2 Tees for procurement point of view.

Full Coupling

Available for size range 1/8″ to 4″ as per ASME B16.11. These are used to connect two small bore plane end pipes.

Half Coupling

Available for size range 1/8″ to 4″ as per ASME B16.11. They are used as small bore branch on big bore lines.

Reducing Coupling

Available for size range 1/8″ to 4″ as per ASME B16.11. These are used to connect pipes of different dimeters. They basically function as reducers.

Unions

SW Union should be screwed tight before the ends are welded, to minimize warping of seat.  Inside Union, ground faced joints are preferred, although other facings are available.

As per Dimensional Standard  : MSS-SP-83, available sizes are 1/8″ to 3″.

Reducing Inserts

Reducing insert is used for connecting a small pipe to a larger fitting. They are available for size range 3/8″ x 1/4″ to 1 1/2″ x 1 1/4″ as per MSS-SP-79. Available ratings are 3000 and  6000 (3M or 6M).

Fittings Classes

Ratings for Socket Welded Fittings are Class 3000, 6000 and 9000.
Choice of Class depends on thickness schedule of pipe, as given in ASME B16.11. Socket welded : 3000:Sch 80 and XS, 6000: Sch 160, 9000:XXS

Materials of Construction

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

Materials of Construction for Forged Piping Fittings

Sample Piping Material Specification

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

  1. Carbon Steel  : ASTM A105. Galvanised, NIC, HIC as per spec.
  2.  Stainless Steel : ASTM A182 F304L
  3. Class SW : 3000:Sch 80 and XS, 6000: Sch 160, 9000:XXS
  4. Ends : Socket Weld Ends, Threaded Female Ends, Dim 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 : Both Ends Plain, Bevelled larger end-Plain Small End (if large size 2” and above).

Elements : Reducer Insert

  1.  Material : CS : ASTM A105,
  2. Class : 3000,
  3. Ends : Socket Weld Ends,
  4. Dim Standard : MSS-SP-79

 

 

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