Pipe Fittings

Butt-Weld (BW) Fittings: The pipe and fitting ends are both bevelled and joined by a full-penetration groove weld. This creates the strongest, most reliable joint — with no crevice, no stress concentration, and weld quality verifiable by RT or UT. Used for 2" NPS and above in high-pressure and high-temperature process piping.

Socket Weld (SW) Fittings: The pipe is inserted into a socket bore in the fitting and fillet-welded externally. The socket provides a gap (approximately 1.5mm) between the pipe end and the socket bore bottom — this is critical to allow for weld shrinkage. No internal weld penetration. Used for small-bore (½"–2") high-pressure piping where the crevice is acceptable.

Threaded Fittings: Male and female NPT (National Pipe Thread) threads provide a mechanical connection without welding. Used for low-to-medium pressure utility and instrument connections where welding is impractical. Cannot be used in NACE sour service or where vibration is significant without additional sealant/locking measures.

All three are self-reinforcing branch connection fittings (olets) to MSS SP-97, but they differ in their branch pipe connection method:

• Weldolet: Branch connection is by butt-weld (BW) — the branch pipe bevelled end is welded into the weldolet with a groove weld. Used for 2" NPS and above branch connections in high-pressure process piping.
• Sockolet: Branch connection is by socket weld (SW) — the branch pipe is inserted into the sockolet socket bore and fillet-welded. Used for ½" to 2" NPS branches in high-pressure service.
• Threadolet: Branch connection is by NPT thread — the branch pipe or fitting is screwed into the threadolet's female NPT thread. Used for instrument take-offs, drain/vent connections, and low-pressure utility branch outlets.

The run-pipe side of all three types is set-on (fillet) welded to the main pipe in the same way. The only difference is the branch connection end.

ASME B16.9 is the American Society of Mechanical Engineers' standard covering the dimensional requirements, wall thickness, tolerances, material requirements, testing, and marking for factory-made wrought butt-welding fittings for all pressure-temperature ratings commonly used in process piping.

It specifies the centre-to-face and end-to-end dimensions for elbows (90° LR, 90° SR, 45°, 180°), tees (equal and reducing), reducers (concentric and eccentric), and end caps in sizes NPS ½" to 48". It also specifies the minimum wall thickness at the mid-section of elbows and tees, which must be at least equal to the ordered wall thickness of the matching pipe minus the applicable pipe mill tolerance.

ASME B16.9 fittings are used globally in ASME B31.3 (Process Piping), ASME B31.4 (Liquid Pipelines), and ASME B31.8 (Gas Transmission Piping) design code systems.

Forged fittings to ASME B16.11 are available in three pressure classes: Class 2000, 3000, and 6000. The class designation refers to the fitting's rated pressure capacity, which must then be derated for temperature per ASME B31.3 Table A-1 (or the applicable code table).

• Class 2000: Available in threaded (NPT) only. Used for low-to-medium pressure utility services.
• Class 3000: Available in both socket weld and threaded configurations. Most common class for process piping small-bore connections.
• Class 6000: Available in both socket weld and threaded. Used for high-pressure instrument and process connections — chemical injection, hydraulic control, high-pressure test connections.

For ASTM A105N carbon steel: Class 3000 SW is rated approximately 5,000 psi at ambient temperature; Class 6000 is approximately 10,000 psi. Always verify for your specific service temperature and fluid using the applicable ASME B31 code allowable stress tables.

Yes. Naftaar can supply pipe fittings compliant with NACE MR0175 / ISO 15156 for hydrogen sulphide (H₂S) sour service. Key requirements for carbon steel fittings in sour service include:

• ASTM A105N (normalised) for forged fittings — max. hardness 22 HRC / 250 HBW after any heat treatment
• ASTM A234 WPB for butt-weld fittings, manufactured from NACE-compliant hot-formed or normalized plate/pipe
• Carbon equivalent (CE) within NACE limits for weldability without cracking
• Hardness survey on representative fitting samples
• Supplementary HIC and SSC testing where specified by the project
• Restriction on certain alloy contents (e.g. max. 1% Ni for NACE Part 1 carbon steel)

Please specify NACE MR0175 compliance, H₂S partial pressure, and any additional project-specific requirements in your RFQ.

For butt-weld fittings, the "schedule" refers to the wall thickness of the fitting at the bevel end — which must match the wall thickness of the connecting pipe. You should always specify the schedule (e.g. Sch 40, Sch 80, Sch 160, XXS) so the fitting's bevel end matches the pipe end for a correct groove weld preparation.

For forged fittings (socket weld and threaded), the "schedule" is not specified in the same way — instead, the pressure Class (2000, 3000, or 6000) determines the fitting's wall thickness and pressure capacity. The socket bore size is fixed per NPS and will accept the standard OD pipe for that NPS.

When submitting an RFQ for butt-weld fittings, always specify: NPS, schedule (e.g. Sch 40, Sch 80), fitting type (e.g. 90° LR elbow), material/grade (e.g. ASTM A234 WPB), and standard (ASME B16.9).

Yes. Naftaar can supply duplex stainless (UNS S31803 / ASTM A815) and super duplex (UNS S32750) butt-weld fittings to ASME B16.9 and forged fittings to ASME B16.11 for offshore and FPSO topside applications. For class-society approved projects, we can co-ordinate third-party inspection by Bureau Veritas, DNV-GL, Lloyd's Register, ABS, or Bureau Veritas — providing the class-accepted inspection certificates required by FPSO vessel specifications.

Additional requirements for offshore duplex/super duplex fittings typically include: ferrite content measurement (FN number), delta-ferrite content by magnetic balancing or ASTM A923 intermetallic phase test, NACE MR0175 compliance (if sour service), impact testing at specified temperature, and PMI confirmation. Please provide your project specification in your RFQ.

PWHT (Post-Weld Heat Treatment) is a controlled heating and cooling process applied to welded piping joints after welding to relieve residual stresses, temper any undesirable hard microstructures in the heat-affected zone (HAZ), and restore ductility. It is required by ASME B31.3 for certain material grades and thicknesses.

PWHT is mandatory after welding for the following pipe fitting material grades (check ASME B31.3 Table 331.1.1 for full requirements):

• ASTM A234 WP91 and WP92 — always requires PWHT (760°C ± 10°C)
• ASTM A234 WP22 — required for wall thickness above 19mm or if hardness exceeds 200 HBW after welding
• ASTM A234 WP11 — required for wall thickness above 19mm at temperatures above 343°C
• High-carbon carbon steel fittings above certain wall thicknesses

Naftaar can provide fittings with the applicable mill heat treatment applied. For WP91 and WP92, we supply fittings in the normalised-and-tempered condition as required for PWHT-compatible weld repair.