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ALLOY 347 / 347H


Stainless Steel 347 / AMS 5512 / AMS 5646 / 347H Alloy

Applications of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :

Alloy 347 (S34700) is stabilized stainless steel plate which offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 347 stainless steel is stabilized by the addition of columbium and tantalum.

Alloy 347 stainless steel is also advantageous for high temperature service because of its good mechanical properties. Alloy 347 stainless steel offers higher creep and stress rupture properties than Alloy 304 and particularly Alloy 304L, which might also be considered for exposures where sensitization and intergranular corrosion are concerns. Alloy 347 (UNS S34700) is columbium stabilized austenitic stainless steel plate with good general corrosion resistance and somewhat better resistance in strong oxidizing conditions than 321 (UNS S32100). It also possesses good low temperature toughness.

Alloy 347H (UNS S3409) stainless steel is the higher carbon (0.04 – 0.10) version of the alloy. It was developed for enhanced creep resistance and for higher strength at temperatures above 1000°F (537°C). In most instances, the carbon content of the plate enables dual certification.Alloy 347 Stainless Steel cannot be hardened by heat treatment, only by cold working. It can be easily welded and processed by standard shop fabrication practices.347 and 347H stainless steel is common in the petroleum refining industries. Alloy 347 and 347H stainless steel is used to make radiant super heaters, boiler tubes, high pressure steam pipe, and general refinery piping. They are also used for heavy-duty exhaust systems and manifolds.


Properties of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :

Alloy 347 stainless steel is austenitic stainless steels that contain stabilizing elements. This alloy is easily welded. Annealing may not be required after welding unless stress relief is desired. 347 Stainless Steel has excellent resistance to oxidation and corrosion. With high creep strength, 347 stainless steel work best up to 1600 °F. The addition columbium plus tantalum in 347 Stainless Steel give some desired characteristics like:

  • Prevents harmful carbide precipitation in the heat affected zone (HAZ) of the weld area
  • Imparts substantial immunity to intergranular corrosion
  • Reduced embrittlement in the HAZ of the weld area


Applications of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :

  • Chemical Processing
  • Food Processing – equipment and storage
  • Petroleum Refining – fluid catalytic cracking units, polyphonic acid service
  • Pharmaceutical Production
  • Waste Heat Recovery – recuperators


Technical Data Sheet of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :

Chemical Composition Limits / Chemistry of SS 347 / 347H
Weight% C P Si Ni Mn S Cr Cb + Ta Fe Co Mo Cu
347 0.08 max 0.040 max 1.00 max 43443 2.0 max 0.030 max 17-19 10 x C min Bal

1.00 max only AMS 5646

0.75 max 0.75 max
347H 0.04-0.10 0.040 max 1.00 max 43443 2.0 max 0.030 max 17-19 10 x C min Bal      


Alloy 347 is generally used where corrosive conditions are severe, such as aircraft exhaust stacks, manifolds and ring collectors. Type 347 is also used for heavy welded assemblies which cannot be annealed after welding or where the operating conditions cause exposure within the temperature range between 800° to 1500°F.


Typical Mechanical Properties of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :  

Material Yield Strength (ksi) Tensile Strength (ksi) % Elongation Hardness HB
Alloy 347Sheet (Sol Trtd)AMS 5512 25   70-105   40   -  
Alloy 347Bar (Sol Trtd)AMS 5646 -   -   -   255 max  


Availability of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :
Alloy 347 is available in Sheet, Plates, Bars (Flat, Hex, Round, Square), Forging Stock, Tube , Welding Wire. 347 Foil (Shim) is available in various thicknesses.

Type Sizes Schedules ASTM Standards
Bar 1/2" to 12"   A276, A479
Butt Weld Fittings 1/2" to 12" Sch 10, 40, 80, 160 & XXH A403
Forgings 1/2" to 12"   A182
Pipe Welded & Seamless 1/2" to 12" Sch 10, 40, 80, 160 & XXH A312
Tube, Welded 1/2" to 12" Sch 10, 40, 80, 160 & XXH A249
Tube, Seamless 1/2" to 12" Sch 10, 40, 80, 160 & XXH A213
Plate 4mm to 100 mm   A240
Flange & Pressure Fittings All Descriptions    

Specifications of Alloy Steel AISI 347 / AISI 347H / UNS S34700 / UNS S34709 :

Stainless Steel 347 /347H Pipe Stainless Steel 347 /347H Seamless
Stainless Steel 347 /347H Tube Stainless Steel 347 /347H Welded / ERW
Stainless Steel 347 /347H Plate Stainless Steel 347 /347H Sheet
347 / 347H ASTM A240 / ASME SA240
AMS 5512 Sheet / strip / plate ASTM A167 / ASME SA167
AMS 5512 Steel, Corrosion and Heat resistant ASTM A276 / ASME SA276
AMS 5512 Sheet, Strip and Plate 18Cr 10.5Ni) ASTM A314 / ASME SA314
AMS 5556 Seamless/ welded tube ASTM A479 / ASME A479
AMS 5558 Welded /thin wall tube BS 2S130
AMS 5571 Seamless tube BS 2T66 Tube
AMS 5575 Welded tube BS T72 Tube
AMS 5646 Bars / wire / forging BS S527 Sheet
AMS 5654 Bars (aircraft quality) BS 970; 347S17
AMS 5674 Wire EN58F / EN58G
AMS 5680 Wire MSRR 6522
QQ-S-763 MSRR 6524
MIL-T-6737 WS 1.4544
MIL-T-8606 Seamless tube WS 1.4546
MIL-T-8606 Welded tube  WS 1.4550
MIL-T-8808 Seamless tube WS 1.5446*Tube
MIL-T-8808 Welded tube AFNOR Z6CNNb18-11
MIL-S-6721 UNS S30347

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