Butt-Welding Fitting

Butt-weld fittings or wrought fittings are the most common type of steel fittings used for pipelines mostly above 4 inches in diameter. Pipe fittings change the pathway of the pipeline (elbows with 45, 90 and 180 degrees angle curve), reduce/increase its flow conveyance capacity (concentric and eccentric reducers), branch (tees, cross) or blind it (butt weld cap). These fittings are supplied with ends chamfered for connection to pipe by means of butt welding.

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Elbow
LR, SR, Reducing and Mitered

Tee
Straight, Reducing, Cross

Reducer
Concentric, Eccentric

Lateral
For Low-pressure applications

Cap
To block off the end of a line

Lap Joint Stub-End
It is mated with a lap joint flange

Highlights of the Butt-Welding Fittings

Specification

• ASME B16.9, ASME B16.28 and, MSS SP43 are the key specifications covering the dimensions and the manufacturing tolerances of butt weld fittings. ASME B16.25 covers the preparation of butt weld connections between pipes and fittings. ASME B16.49 covers the marking details.

• The wrought ﬁtting materials conform to ASTM A234, A403, or A420, the grades of which have chemical and physical properties equivalent to that of the mating pipe.

Pressure Test

• Pressure testing of the ﬁttings is not required by either standard. However, the ﬁttings are required to be capable of withstanding, without leakage, a test pressure equal to that prescribed in the speciﬁcation of the pipe with which the ﬁtting is recommended to be used.

Disadvantage

• One of the major disadvantages of butt-welded systems is that they are not easy to dismantle.

Cost

• Material costs are low, but labor costs are moderate to high due to the need for specialized welders and ﬁtters.

Size

• Most butt-welded piping installations are limited to NPS 2¹⁄₂ (DN65) or larger. There is no practical upper size limit in butt-welded construction.

• Butt-welding ﬁttings and pipe system accessories are available down to NPS ¹⁄₂ (DN15). However, economic penalties associated with pipe end preparation and ﬁt-up, and special weld procedure qualiﬁcations normally preclude the use of butt-welded

Other Properties

• The interior surface of a butt-welded piping system is smooth and continuous which results in low pressure drop.

• The system can be assembled with internal weld backing rings to reduce ﬁt-up and welding costs, but backing rings create internal crevices, which can trap corrosion products. In the case of nuclear piping systems, these crevices can cause a concentration of radioactive solids at the joints, which can lead to operating and maintenance problems. Backing rings can also lead to stress concentration effects, which may promote fatigue cracks under vibratory or other cyclic loading conditions. Butt-welded joints made up without backing rings are more expensive to construct, but the absence of interior crevices will effectively minimize ‘‘crud’’ buildup and will also enhance the piping system’s resistance to fatigue failures.

Materials

ASTM A403 WP (Gr. 304, 304H, 304L, 309, 310, 316, 316L, 317L, 321, 347, 904L)

ASTM A420 WPL3 , A420 WPL6

ASTM A234 WPB , WPBW, WPHY 42, WPHY 46, WPHY 52, WPH 60, WPHY 65 and WPHY 70

ASTM A234 (Gr. WP1, WP5, WP9, WP11, WP12, WP22, WP91)

ASTM A860 (WPHY 42 - WPHY 46 - WPHY 52 - WPHY 56 - WPHY 60 - WPHY 65 - WPHY 70 - WPHY 80 only as per MSS-SP75)

ASTM A815 (UNS S31803, S32205, S32760, S32750)

Standard

ASME B16.9, ASME B16.28 and, MSS SP43 are the key specifications covering the dimensions and the manufacturing tolerances of butt weld fittings. ASME B16.25 covers the preparation of butt weld connections between pipes and fittings and ASME B16.49 covers the marking details.

ASME B16.9 and B16.28

This Standard covers overall dimensions, tolerances, ratings, testing, and markings for wrought carbon and alloy steel factory-made butt-welding fittings of NPS 1/2 through 48. It covers fittings of any producible wall thickness. This standard does not cover low pressure corrosion resistant butt-welding fittings. See MSS SP-43, Wrought Stainless Steel Butt-Welding Fittings. Short radius elbows and returns, which were previously included in ASME B16.28-1994, are included in this standard. B16.9 is to be used in conjunction with equipment described in other volumes of the ASME B16 series of standards as well as with other ASME standards, such as the Boiler and Pressure Vessel Code and the B31 Piping Codes”. (source: ASME)

MSS SP 43

The MSS SP 43 sets the dimensions, tolerances, and markings for butt weld fittings for low pressure, corrosion resistant applications. It covers only fittings for use with Schedule 5S or 10S pipe, for all NPS sizes listed in ASME B36.19M, except that for short pattern stub ends suitable for use with Schedule 40S are also shown. Essentially, MSS SP 43 is the reference standard for lightweight corrosion resistant butt weld fittings (stainless steel, duplex).

ASME B16.25

ASME B16.25 sets standards for the preparation of the ends of components that need to be welded together. As stated in the ASME website: “This Standard covers the preparation of butt-welding ends of piping components to be joined into a piping system by welding. It includes requirements for welding bevels, for external and internal shaping of heavy-wall components, and for preparation of internal ends (including dimensions and tolerances). Coverage includes preparation for joints with the following: no backing rings; split or non-continuous backing rings; solid or continuous backing rings; consumable insert rings; gas tungsten arc welding (GTAW) of the root pass” (source: ASME).

ASME B16.49

The ASME B16.49 Norm covers the manufacturing, marking, design, material, testing, and inspection requirements for factory-made bends of carbon steel materials having controlled chemistry and mechanical properties, produced by the induction bending process, with or without tangents. This standard covers induction bends for transportation and distribution piping applications (e.g., ASME B31.4, B31.8, and B31.11).