SS 347 & 347H Seamless Tubes Manufacturer
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Midland Alloys Inc. is a leading manufacturer and supplier of SS 347 & 347H seamless tubes, offering high-performance niobium-stabilised austenitic stainless steel tubing for high-temperature conditions. We manufacture tubes that can endure extreme temperatures where normal grades may fail due to intergranular corrosion. Our 347H type has a regulated increased carbon content, which significantly increases creep resistance and strength at temperatures above 538°C. By focusing on the seamless manufacturing procedure, we reduce the risks associated with longitudinal welds, ensuring that each tube provides excellent structural durability under high pressure. As a leading 347 seamless tube exporter, we provide precision-tested products to industries that cannot afford delays. Our products undergo extensive quality control procedures to ensure that each batch of high-temperature stainless steel seamless tubes meets international standards. We manage logistics for worldwide shipping as well as thorough documentation.
What is SS 347 & 347H Seamless Tubing?
SS 347 and 347H seamless tubing refers to niobium‑stabilised austenitic stainless steel tubes engineered for elevated temperature service. Seamless tubes form through extrusion or pilgering, without longitudinal welds, which removes weak points under pressure or thermal cycling. Niobium plays a key role here. It ties up carbon and prevents chromium carbide precipitation at grain boundaries during high‑heat exposure. That control protects corrosion resistance after welding or long service hours. SS 347H is the higher‑carbon variant, specified when greater creep strength and tensile stability are required at sustained temperatures. Both grades meet common tube standards such as ASTM A213 for heat exchangers and boilers, ASTM A269 for general service, and ASTM A312 for pressure piping. In critical service lines, SS 347 seamless tubing and SS 347H stainless steel seamless tubes provide stable performance, where heat and stress combine.
Benefits of SS 347 / 347H Seamless Tubing
Seamless SS 347 and 347H tubing delivers dependable performance in systems exposed to constant heat, pressure, and thermal movement. These grades support long service life where structural stability matters most.
- Intergranular corrosion resistance during prolonged high‑temperature exposure
- High‑temperature strength retention under sustained mechanical loads
- Creep resistance capability for continuous elevated temperature service
- Seamless structural consistency across pressure‑bearing tube sections
- Thermal fatigue stability during repeated heating and cooling cycles
- Oxidation resistance at elevated operating temperatures
- Weld‑zone integrity stability after fabrication and field welding
- Long‑term high‑heat durability in critical process environments
Engineers value the SS 347 seamless tube benefits and 347H seamless tubing advantages for systems that cannot afford distortion or early material fatigue.
Specifications of SS 347 / 347H Seamless Tubes
We provide SS 347 and 347H seamless tubes with dimensions and tolerances that exceed high-temperature pressure service requirements, complying with worldwide regulations and project specifications.
Seamless Tube OD : 1 / 2" NB - 16" NB
ASTM A213, A269, A249, A511, A554 / ASME SA213, SA269, SA249, SA511, SA554
Seamless
Round, Square, Rectangular, Hydraulic Etc
Single Random, Double Random, Standard & Cut length
Plain Ends (PE), Threaded Ends (TE), Bevelled Ends (BW), Grooved Mechanical Joints or Grooved Ends, TBE (Treaded Both Ends)
SCH 5, SCH10, SCH 40, SCH 80, SCH 80S, SCH 160, SCH XXS, SCH XS
2B, No.4, No.1, No.8 Mirror Finish for Stainless Steel Tubes, Finish as per customer Requirements
Types of Stainless Steel 347 & 347H Seamless Tubing
Industrial systems require various shapes to handle different stress loads and fluid dynamics, especially in heat-intensive zones. We manufacture various SS 347 seamless tube types to fit these specific mechanical requirements.
Pipe Forms
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Round TubeIdeal for high-temperature fluid, and gas transfer in refineries.
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Square TubeProvides structural support near heat-affected zones in heavy machinery.
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Rectangular TubeFrequently used for furnace frameworks and equipment support structures.
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Boiler TubeSpecifically engineered for high-pressure steam and superheater applications.
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Heat Exchanger TubeDesigned for effective heat transmission in high-temperature applications.
Each of these 347H seamless tube forms is meticulously measured to ensure a correct fit into existing headers or manifolds.
Contact us today to discuss how Stainless Steel 347/347H Seamless Tubes can benefit your application. Whether you need guidance in selecting the right Tubes or have specific requirements, our team of experts is here to help you find the optimal solution.
Technical Details & Delivery Condition
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N | |
| 347 | min. | – | – | – | – | – | 17.0 | 2.00 | 9.0 | – |
| max. | 0.08 | 2.0 | 1.00 | 0.045 | 0.030 | 20.0 | 3.00 | 13.0 | – | |
| 347H | min. | 0.04 | – | – | – | – | 17.0 | 3.00 | 9.0 | – |
| max. | 0.10 | 2.0 | 1.00 | 0.045 | 0.030 | 19.0 | 4.00 | 13.0 | – | |
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N | |
| 347 | min. | – | – | – | – | – | 17.0 | 2.00 | 9.0 | – |
| max. | 0.08 | 2.0 | 1.00 | 0.045 | 0.030 | 20.0 | 3.00 | 13.0 | – | |
| 347H | min. | 0.04 | – | – | – | – | 17.0 | 3.00 | 9.0 | – |
| max. | 0.10 | 2.0 | 1.00 | 0.045 | 0.030 | 19.0 | 4.00 | 13.0 | – | |
Stainless Steel Seamless Tubes Grades We Offer
Round Bar
Analytic
Cut to Length
Centering
Heating
Perforation
Inspection of Size
Pickling
Inspection of Surface
Lubricating
Cold Drawing (Cold Rolling)
Degreasing
Annealing
Straightening
Cut
Pickling / Passivating
Inspection
Analytic
Marking
Packing & Shipping
Industrial Applications of SS 347 / 347H Seamless Tubes
The unique chemical composition of these tubes makes them indispensable across several high-pressure industries. In the power generation industry, they serve as the primary conduits in boilers and superheaters where steam temperatures are punishing. Petrochemical plants rely on SS 347 seamless tube applications for high-temperature catalytic cracking units and hydrodealkylation systems. Because the material doesn’t lose its strength easily, it is also found in heat exchangers and condensers handling corrosive exhaust gases. Many furnace operators use these for thermal processing equipment and radiant tubes. Even the aerospace sector uses them for exhaust manifolds and engine parts where vibration meets high heat. For these reasons, 347H stainless steel tubing uses are common in any facility where the temperature exceeds the safety limits of basic stainless steels. Reliability is non-negotiable in these fields.
Why Choose SS 347 / 347H Seamless Tubes from Midland Alloys Inc.
Midland Alloys Inc. provides seamless tube with stringent metallurgical control for high-temperature grades where carbon balancing and niobium stability have a direct impact on durability. Precision cold drawing and regulated heat treatment ensure uniform wall thickness, and a stable grain structure under prolonged heat stress. Before shipping each tube is examined for dimensional checks, chemical analysis, mechanical testing, and nondestructive inspection to ensure that it meets ASTM and ASME requirements. In critical refinery and power plant zones, regular monitoring of the niobium-to-carbon ratio reduces the risk of carbide-related issues. Complete documentation, including MTCs and ultrasonic test reports, ensures full traceability. Export-ready packing, including hardwood crates, and protective end caps, ensures surface quality during shipment. This systematic methodology ensures material reliability and logistical assurance for projects carried out globally, with no delays or compliance gaps.
FAQs – SS 317/317H Seamless Tubes
SS 347 / 347H seamless tubes are used in high‑temperature pressure systems such as boilers, heat exchangers, furnaces, and power plant piping where creep resistance and oxidation control are critical.
Niobium stabilises carbon, preventing carbide precipitation at grain boundaries during high‑temperature exposure and post‑weld service.
SS 347H suits applications requiring higher strength retention and creep resistance at sustained elevated temperatures.
