Stainless Steel 347 Pipes: Properties, Manufacturing

Some stainless steel pipes spend their working life in heat that would ruin ordinary grades. In refineries, power plants and chemical units, pipes can run for years at temperatures where standard austenitic steels become vulnerable to cracking and corrosion. Grade 347 was developed for exactly these conditions. This guide explains what makes it special, how the pipes are made and what to check when you contact a stainless steel 347 pipes manufacturer or supplier.

What is grade 347 stainless steel?

Grade 347 (UNS S34700) is an austenitic stainless steel stabilised with niobium, also called columbium. Its base composition is similar to 304, with roughly 17 to 19 percent chromium and 9 to 13 percent nickel, but the added niobium changes how it behaves at high temperature.

Without stabilisation, austenitic stainless steels can form chromium carbides when held between about 425 and 815 degrees Celsius, or when welded. These carbides form at grain boundaries and deplete the surrounding steel of chromium, causing a weakness known as sensitisation. This leaves the steel prone to intergranular corrosion. Niobium bonds with carbon first, forming niobium carbides and leaving chromium free to protect the metal.

347 versus 347H

There is also grade 347H (UNS S34709), which has a higher carbon range of about 0.04 to 0.10 percent. The extra carbon improves creep strength and high-temperature performance, so 347H is often chosen for long-term service at elevated temperatures. Standard 347 has a lower carbon limit and is common where welding and corrosion resistance matter most. The right choice depends on temperature, pressure and expected service life.

Key properties

• Resistance to intergranular corrosion after welding or exposure to sensitising temperatures
• Good high-temperature strength and oxidation resistance
• Excellent weldability without the need for post-weld annealing in many cases
• General corrosion resistance comparable to 304
• Good toughness across a wide temperature range

Grade 321 is a similar stabilised steel that uses titanium instead of niobium. Many engineers prefer 347 for welded structures, since niobium is more stable through the welding process than titanium.

Common applications

Stainless steel 347 pipes are found where heat and corrosion meet:

• Oil refineries and petrochemical plants
• Power generation and boiler systems
• Heat exchangers and process heaters
• Exhaust and furnace components
• Chemical processing and high-temperature piping
• Aerospace and industrial gas turbines

How seamless 347 pipes are manufactured

Understanding the process helps you ask better questions of any supplier. Seamless pipe manufacturing generally follows these steps:

1. Billet selection. Solid round billets of grade 347 are produced with carefully controlled chemistry, including the niobium content.
2. Heating and piercing. The billet is heated and pierced over a mandrel to form a hollow shell.
3. Hot working or extrusion. The shell is rolled or extruded to approximate size.
4. Cold drawing or pilgering. For tighter tolerances and better surface quality, the pipe is cold finished.
5. Solution annealing. The pipe is heated to a high temperature and cooled quickly, dissolving carbides and restoring corrosion resistance and ductility.
6. Pickling and cleaning. Acid cleaning removes scale and gives a clean, uniform surface.
7. Straightening and cutting. Pipes are straightened and cut to the required length.
8. Testing and inspection. Dimensional checks, hydrostatic or non-destructive tests and chemical analysis confirm quality.
9. Marking and packing. Each pipe is marked with grade, size, standard and heat number before packing.

Standards and specifications

Common specifications for 347 pipes and tubes include:

• ASTM A312 / ASME SA312 for seamless and welded austenitic pipes
• ASTM A213 / ASME SA213 for seamless boiler, superheater and heat exchanger tubes
• ASTM A269 / ASME SA269 for general service tubing

Always state the grade (347 or 347H), the standard, outside diameter, wall thickness or schedule, length and finish when requesting a quotation. The principle reason for disputes between buyers and suppliers is an incomplete specification, so be precise.

What to ask a stainless steel 347 pipes supplier

Before you place an order, ask these questions:

• Can you supply mill test certificates to EN 10204 3.1?
• What testing is included, such as PMI, hydrostatic testing or intergranular corrosion tests?
• Do you hold ready stock, and what is the lead time for non-standard sizes?
• Which standards and sizes can you supply?
• How do you pack pipes for export?
• Can you provide third-party inspection if required?

Why choose Yash Impex?

Yash Impex is a Government of India recognised export house and an ISO 9001:2015 certified company, with around 50 years of experience in engineering products. Its stainless steel range comprises of grades 304, 316, 317, 321, 347 and 904L, in standards such as ASTM A312, A213 and A269. Its clients span more than 15 countries, including markets in Africa and the Middle East, and it can also supply flanges and fittings alongside pipes, which simplifies sourcing.

Request a quote

If you are looking for stainless steel 347 pipes, share your specification, quantity and delivery location with the team at Yash Impex for a prompt quotation.