Metinox overseas is the supplier and manufacturer of SS 347 Pipe Fittings in India with a complete set of ASTM A403 WP347 and WP347H fittings which are used in industrial demanding applications. Our SS 347 / 347H Pipe Fittings are columbium (niobium) and tantalum stabilized austenitic stainless steel fittings that are produced as per high international standards and are used in petroleum refineries, aerospace applications, power generation plants, nuclear facilities and chemical processing units all over the world.
In contrast to SS 321 which has titanium as a stabilizing element, SS 347 has columbium (niobium) and tantalum as stabilizers. This is the major distinction that makes SS 347 Pipe Fittings much better than SS 321 in the conditions that are likely to experience polythionic acid stress corrosion cracking (SCC) and intergranular corrosion that is the most important design consideration in petroleum refinery piping systems. SS 347 also exhibits better performance in creep and stress rupture when compared to SS 304 and SS 304L and in aqueous and low-temperature corrosive environments when compared to SS 321.
We supply SS 347 Buttweld Fittings and SS 347H Pipe Fittings conforming to UNS S34700 / S34709, DIN 1.4550 / 1.4961, and WERKSTOFF 1.4550 / 1.4961, with material test certificates as per EN 10204 3.1 / 3.2. We have export inventory of 1/2" -48" NB fittings in schedule 5S to XXS.
Request a quote now!The following table summarizes the primary specification details for SS 347 Pipe Fittings supplied by Metinox Overseas:
| Grade | UNS No. | DIN / Werkstoff | Carbon (C%) |
|---|---|---|---|
| WP347 | S34700 | DIN 1.4550 / W. 1.4550 | 0.08 max |
| WP347H | S34709 | DIN 1.4961 / W. 1.4961 | 0.04 to 0.10 |
All SS 347 Buttweld Fittings and Stainless Steel 347 Buttweld Fittings are manufactured to ASTM A403 and ASME B16.9 dimensional standards. Available forms include seamless and welded construction, with 100% X-Ray testing available on request for critical service applications
| Spec | Grade | UNS No. | Finish | Test Cert | Delivery |
|---|---|---|---|---|---|
| ASTM A403 | WP347 / WP347H | S34700 / S34709 | As Per Order | EN 10204 3.1 / 3.2 | Seamless and Welded |
Understanding the difference between SS 347 and SS 347H is critical when selecting the right SS 347 / 347H Pipe Fittings for your application. Both grades are columbium (niobium) and tantalum stabilized, but their carbon content and high-temperature performance differ significantly:
| Property | SS 347 | SS 347H |
|---|---|---|
| UNS Number | S34700 | S34709 |
| DIN / Werkstoff | 1.4550 | 1.4961 |
| Carbon Content | 0.08% max | 0.04% to 0.10% |
| Niobium + Tantalum | 10x C min (Nb+Ta) | 8x C min (Nb+Ta) |
| Max Service Temp | Up to 900°C | Above 538°C (creep service) |
| Key Advantage | General high-temp and aqueous service | Superior creep and stress rupture strength |
| Typical Applications | Refinery piping, chemical plants | Aerospace exhaust, steam service, bitumen upgraders |
SS 347H (UNS S34709 / DIN 1.4961) has a higher carbon content of 0.04% to 0.10%, which results in significantly superior creep strength and stress rupture properties above 538 degrees Celsius. This makes SS 347H Pipe Fittings the preferred choice for aerospace exhaust systems, petroleum refining steam services, and bitumen upgrader piping, where long-term elevated-temperature strength is a non-negotiable requirement.
The most common decision engineers face when specifying stabilized austenitic stainless fittings is the choice between SS 321 and SS 347. The table below provides a definitive comparison for engineers specifying refinery and industrial fittings:
| Property | SS 321 Fittings | SS 347 Fittings |
|---|---|---|
| Stabilizing Element | Titanium (Ti) | Columbium / Niobium + Tantalum (Nb + Ta) |
| UNS Number | S32100 | S34700 |
| Polythionic Acid SCC Resistance | Poor | Excellent (preferred for refineries) |
| Aqueous Corrosion Resistance | Moderate | Superior |
| Low-Temp Corrosion Resistance | Moderate | Superior |
| Weldability (Ti loss) | Ti loss in weld pool possible | No Nb loss; weld integrity maintained |
| Creep Strength (base grade) | Good | Comparable; 347H is significantly superior |
| Typical Use Case | General high-temp service | Petroleum refining, polythionic acid environments |
| Price Level | Moderate | Moderate to slightly higher |
For petroleum refinery piping where the process gas or condensate contains sulfur compounds that form polythionic acid during shutdowns, SS 347 Pipe Fittings are the only stabilized-grade fittings that provide reliable protection against polythionic acid SCC. Specifying SS 321 in such environments introduces an unacceptable risk of stress corrosion cracking at sensitized weld heat-affected zones.
Polythionic acid stress corrosion cracking (SCC) is a failure mechanism that affects sensitized austenitic stainless steel in refinery environments. During plant shutdowns, when moist air contacts sulfide deposits on the internal surface of piping, polythionic acids (H2SxO6) form. These acids attack sensitized weld heat-affected zones, leading to intergranular cracking that can cause catastrophic failures.
Refinery engineers in hydrodesulfurization, fluid catalytic cracking, and atmospheric distillation units routinely specify ASTM A403 WP347 fittings as the mandatory material of construction wherever polythionic acid SCC risk has been identified. Metinox Overseas supplies these fittings with full ASTM A403 compliance, complete material traceability, and EN 10204 3.1 certification.
Metinox Overseas manufactures and supplies the complete range of SS 347 / 347H Pipe Fittings in all standard types as per ASME B16.9, ASME B16.28, and MSS SP-43 / SP-75:
All SS 347 Buttweld Fittings are available in both seamless and welded construction, with or without 100% radiographic examination. Custom fabricated fittings and special end preparations are available on request.
The chemical composition of ASTM A403 WP347 and WP347H pipe fittings, including the critical columbium (niobium) and tantalum stabilizer content, is given below:
| Grade | C% | Mn% | Si% | Cr% | Ni% | Nb+Ta% | P% max |
|---|---|---|---|---|---|---|---|
| WP347 | 0.08 max | 2.00 max | 0.75 max | 17.0 to 19.0 | 9.0 to 13.0 | 10xC min | 0.045 |
| WP347H | 0.04 to 0.10 | 2.00 max | 0.75 max | 17.0 to 19.0 | 9.0 to 13.0 | 8xC min | 0.045 |
The key feature of the chemical composition of SS 347 Pipe Fittings is the Nb+Ta content, which is a minimum of 10 times the carbon content for WP347 and 8 times the carbon content for WP347H. This stabilizer-to-carbon ratio is what ensures effective grain boundary stabilization and resistance to intergranular corrosion and polythionic acid SCC.
The mechanical properties of SS 347 / 347H Pipe Fittings per ASTM A403 at room temperature are as follows:
| Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation % | Hardness (HRB max) |
|---|---|---|---|---|
| WP347 | 515 min | 205 min | 35 min | 92 |
| WP347H | 515 min | 205 min | 35 min | 92 |
SS 347H offers significantly higher creep and stress rupture strength above 538 degrees Celsius compared to standard SS 347. This is due to the higher carbon content in SS 347H (UNS S34709 / DIN 1.4961), which contributes to a more stable microstructure at elevated temperatures and superior resistance to time-dependent deformation under sustained load.
When specifying SS 347 / 347H Pipe Fittings for international projects, engineers often work with multiple designation systems. The following table provides the full equivalent grade cross-reference covering UNS, DIN 1.4550 / 1.4961, WERKSTOFF 1.4550 / 1.4961, and EN designations:
| Grade | UNS No. | DIN | Werkstoff No. | EN | AISI |
|---|---|---|---|---|---|
| SS 347 | S34700 | DIN 1.4550 | 1.4550 | X6CrNiNb18-10 | 347 |
| SS 347H | S34709 | DIN 1.4961 | 1.4961 | X8CrNiNb16-13 | 347H |
Metinox Overseas can supply SS 347 Pipe Fittings with material test certificates referencing any of the above equivalent designation systems, enabling compliance with European (PED), North American (ASME), and international project specifications simultaneously.
| Type | Size Range (NB) | Wall Thickness | Schedule |
|---|---|---|---|
| Seamless Fittings | 1/2" to 10" NB | As per ASME B16.9 | SCH 5S to XXS |
| Welded Fittings | 1/2" to 48" NB | As per ASME B16.9 | SCH 5S to XXS |
| Custom / Special | Up to 72" NB on request | Per customer drawing | As required |
Our SS 347 Buttweld Fittings are available across a comprehensive wall thickness range from Schedule 5S through to Double Extra Strong (XXS), covering all standard ASME B36.19M pipe schedules for stainless steel. For sizes beyond 10" NB, welded construction fittings per ASME B16.9 are supplied.
ASTM A403 uses the WP-S, WP-W, and WP-WX suffix designations to indicate the method of construction and level of examination applied to SS 347 / 347H Pipe Fittings. Understanding these designations is important for correct specification:
| Designation | Description | Application |
|---|---|---|
| WP-S (Seamless) | No welds; seamless tube or pipe used | High-pressure, high-temp critical service |
| WP-W (Welded) | Fittings contain weld seam; radiographically tested | General process piping |
| WP-WX (Welded Examined) | Full radiographic examination of entire fitting surface | Critical service where weld integrity is paramount |
For critical petroleum refinery and nuclear service applications, WP-S (seamless) or WP-WX (fully examined welded) SS 347 Pipe Fittings are recommended. Metinox Overseas can supply any of the three construction types based on the project specification requirement.
The following reference table provides wall thickness data for SS 347 Pipe Fittings across common nominal sizes and schedules per ASME B36.19M:
| Nominal Size | OD (mm) | SCH 40 WT (mm) | SCH 80 WT (mm) | SCH 160 WT (mm) | XXS WT (mm) |
|---|---|---|---|---|---|
| 1/2" | 21.3 | 2.77 | 3.73 | 4.78 | 7.47 |
| 1" | 33.4 | 3.38 | 4.55 | 6.35 | 9.09 |
| 2" | 60.3 | 3.91 | 5.54 | 8.74 | 11.07 |
| 4" | 114.3 | 6.02 | 8.56 | 13.49 | 17.12 |
| 6" | 168.3 | 7.11 | 10.97 | 18.26 | 21.95 |
| 8" | 219.1 | 8.18 | 12.70 | 23.01 | 22.23 |
| 12" | 323.8 | 9.53 | 17.48 | 25.40 | 25.40 |
For detailed weight calculations, ASME B16.9 center-to-end dimensions, and custom schedule data for SS 347 / 347H Pipe Fittings, please contact our technical team or request a product datasheet.
SS 347 / 347H Pipe Fittings are specified across a wide range of high-temperature and corrosive-service industries. Key application sectors include:
The standard construction material used in refinery units on polythianic acid SCC design constraint is SS 347 Pipe Fittings. This includes hydrodesulfurization (HDS) and fluid catalytic cracking (FCC), atmospheric and vacuum distillation and amine treating units. The resistance to polythionic acid attack of ASTM A403 (WP347) fittings in the conditions of plant shutdowns is provided with the help of the columbium stabilization, and this failure mode has led to serious accidents in the case of refiners using non-stabilized and titanium-stabilized grades.
Pipe Fittings SS 347H (UNS S34709 / DIN 1.4961) are common in aircraft exhaust manifold systems, jet engine, and missile heat shield connection. The increased carbon in 347H provides the creep rupture strength needed to sustain service at temperatures up to 538 degrees Celsius, the same as needed by aerospace propulsion systems.
The SS 347 Pipe Fittings find an application in high temperature steam headers, superheater outlet pipeline and reheater connections of thermal power plants and combined heat and power (CHP) stations, where creep resistance is necessary, and stability in the weld-zone at operating temperatures are necessary. The fittings are SS 347H which are specified in the hottest superheater and reheater applications.
In non-primary-boundary, reactor support systems and auxiliary piping are detailed in the nuclear power industry using SS 347 / 347H Pipe Fittings. In India, BARC and nuclear utility specifications regularly contain SS 347 butt weld fittings approved by IBR and with 3.2 third-party inspection on EN 10204.
SS 347 Pipe Fittings are installed in chemical reactors, heat exchanger manifolds, process transfer piping in fertilizer, specialty chemical, and upgrader process plants. The high intergranular corrosion resistance of the UNS S34700 fittings is the key element that makes these fittings the choice of preference in the case of elevated-temperature process fluids or acidic condensates.
The price of SS 347 Pipe Fittings in India depends on the grade (WP347 vs WP347H), fitting type, size, schedule, and quantity. SS 347H fittings are priced slightly higher than SS 347 due to tighter chemical control requirements and the higher Nb+Ta content of the alloy.
Metinox Overseas offers competitive ex-works and FOB Mumbai pricing for both domestic and international buyers. We supply to refineries, EPC contractors, and trading houses across the Middle East, Southeast Asia, Europe, and North America.
To receive an updated SS 347 Pipe Fittings price list, contact our sales team with your size, schedule, grade, quantity, and certification requirements.
Complete your SS 347 / 347H piping system with our full range of related products:
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SS 347 Pipe Fittings are stabilized with columbium (niobium), tantalum and SS 321 Pipe Fittings are titanium. The practical difference that is considered critical is that SS 347 is better than SS 321 against polythionic acid stress corrosion cracking, which is a failure mode unique to petroleum refinery piping subjected to sulfide-containing process streams during shutdowns. The SS 347 is also better than SS 321 in the aqueous and low-temperature corrosive environment. To use as refinery service, SS 347 Pipe Fittings (ASTM A403 WP347) should be used over SS 321.
The element niobium is also known as columbium. In SS 347 Pipe Fittings, at least 10 times the carbon content of the alloy is added with the addition of columbium (niobium) and tantalum in the alloy. This is so that the niobium is used preferentially with carbon to make stable niobium carbides and keep chromium off the combination with carbon to create chromium carbides at grain boundaries. The outcome is that SS 347 Pipe Fittings are resistant to intergranular corrosion and polythionic acid SCC despite welding or long-term high-temperature service.
SS 347H Pipe Fittings (UNS S34709 / DIN 1.4961) are provided to have sustained service operating above 538 degrees Celsius where creep and stress rupture are the determining failure modes. The greater carbon content (0.04% to 0.10%) and resultant niobium carbide precipitation in SS 347H provides much higher creep rupture strength than standard SS 347 and other austenitic grades (e.g. SS 304H). The normal maximum service temperatures specified in pressure vessel and piping code of SS 347H would be 900 to 950 degrees Celsius at short term exposure.
ASTM A403 is the standard grade of the wrought austenitic stainless steel pipe fittings. The ASTM A403 designation for the given grade is SS 347 (UNS S34700), designation WP347H is the higher-carbon SS 347H grade (UNS S34709). All SS 347 Buttweld Fittings supplied by Metinox Overseas is made to ASTM A403 WP347 / WP347H and dimensionally fabricated to ASME B16.9.
Metinox Overseas delivers SS 347 / 347H Pipe Fittings with the certificates of the material tests of EN 10204 3.1 as a standard. EN 10204 3.2 third party inspection certificates (of DNV, Bureau Veritas, Lloyds Register, SGS or TUV, etc.) can be requested. Indian Boiler Regulation IBR approval documentation is also made available to projects that have to comply with the Indian Boiler Regulation. Critical service fittings can be supplied with 100 percent radiographic examination and positive material identification (PMI).
Metinox Overseas is a reputable supplier and manufacturer of SS 347 / 347H Pipe Fittings in India and has established a reputation in supplying columbium stabilized stainless steel fittings to various refineries, EPC contractors and engineering firms in 50+ countries. We have export-ready high-demand size and offer a complete documentation package to the international projects.
Send your needs in terms of size, schedule, grade, quantity, and certification requirement to our sales force to obtain a quote of ASTM A403 WP347 fittings or SS 347H Buttweld Fittings or any other related product. Our response takes place within 24 hours.
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