ASTM A312 TP347H Seamless Pipe

ASTM A312 TP347H Stainless Steel Seamless Pipe 

Stainless steel alloy 347/347H is a stabilized, austenitic, chromium steel containing columbium which allows for the elimination of carbide precipitation, intergranualr corrosion. 347 is stabilized by the additions of chromium and tantalum and offers higher creep and stress rupture properties than alloy 304 and 304L which may also be used for exposures where sensitization and intergranualr corrosion are of concern. The addition of columbium also allows Alloy 347 to have excellent corrosion resistance, even superior to that of alloy 321.  347H is the higher carbon composition form of Alloy 347 and demonstrates improved high temperature and creep properties. 

Benefits of 347 Stainless Steel

-Higher creep stress and rupture properties when compared with 304

-Ideal for high temperature service

-Overcomes sensitization and intergranular corrosion concerns

-Can be used in elevated temperature applications for ASME Boiler and Pressure Vessel Code applications

-Due to stabilisation the material offers better overall corrosion resistance when compared to 304/304L

-Excellent mechanical properties

-A high carbon version (347H) is also available

Typical Uses

-Heat exchangers

-High temperature steam service

-High temperature chemical process

-Both 347/347H are used primarily in elevated temperature applications.

Chemical Composition of 347 Stainless Steel Pipes and Tubes
Represented by ASTM A240 and ASME SA-240 specifications.

 Physical Properties of 347 Stainless Steel Pipes and Tubes

 The physical properties of Types 321 and 347 are quite similar and, for all practical purposes, may be considered to be the same. The values given in the table may be used to apply to both steels.

When properly annealed, the Alloys 321 and 347 stainless steels consist principally of austenite and carbides of titanium or columbium. Small amounts of ferrite may or may not be present in the microstructure. Small amounts of sigma phase may form during long time exposure in the 10000F to 15000F (5930C to 8160C) temperature range.

The stabilized Alloys 321 and 347 stainless steels are not hardenable by heat treatment.

The overall heat transfer coefficient of metals is determined by factors in addition to thermal conductivity of the metal. In most cases, film coefficients, scaling, and surface conditions are such that not more than 10 to 15% more surface area is required for stainless steels than for other metals having higher thermal conductivity. The ability of stainless steels to maintain clean surfaces often allows better heat transfer than other metals having higher thermal conductivity.

Mechanical Properties of 347 Stainless Steel Pipes and Tubes

Room Temperature Tensile Properties

Minimum mechanical properties of the stabilized Alloys 321 and 347 chromium-nickel grades in the annealed condition (20000F [10930C], air cooled) are shown in the table.

Elevated Temperature Tensile Properties

Typical elevated temperature mechanical properties for Alloys 321 and 347 sheet / strip are shown below. Strength of these stabilized alloys is distinctly higher than that of non-stabilized 304 alloys at temperatures of 10000F (5380C) and above.

High carbon Alloys 321H and 347H (UNS32109 and S34700, respectively) have higher strength at temperatures above 10000F (5370C). ASME maximum allowable design stress data for Alloy 347H reflects the higher strength of this grade in comparison to the lower carbon Alloy 347 grade. The Alloy 321H is not permitted for Section VIII applications and is limited to 8000F (4270C) use temperatures for Section III code applications.

Heat Treatment of 347 Stainless Steel Pipes and Tubes

 The annealing temperature range for Alloys 321 and 347 is 1800 to 20000F (928 to 10930C). While the primary purpose of annealing is to obtain softness and high ductility, these steels may also be stress relief annealed within the carbide precipitation range 800 to 15000F (427 to 8160C), without any danger of subsequent intergranular corrosion. Relieving strains by annealing for only a few hours in the 800 to 15000F (427 to 8160C) range will not cause any noticeable lowering in the general corrosion resistance, although prolonged heating within this range does tend to lower the general corrosion resistance to some extent. As emphasized, however, annealing in the 800 to 15000F (427 to 8160C) temperature range does not result in a susceptibility to intergranular attack.For maximum ductility, the higher annealing range of 1800 to 20000F (928 to 10930C) is recommended.