Why? Why? Why? 316Ti – UNS S31635

It is common to find a connection to a German equipment manufacturer or design. However, 316Ti is practically non-existent in North American inventory, and usually requires a mill production run.

Titanium is used as a stabilizing element in austenitic stainless steels with higher carbon contents, and will reduce the formation of chromium carbides. It can improve the aqueous corrosion resistance of welds made in higher carbon grades. Actually, 316Ti is a derivative of 316 in the same way that 321 is related to 304. In fact, 321 is the titanium stabilized version of 304, but while 321 is common in the petrochemical and aerospace industries, 316Ti is not.

Chemical Composition Comparison – Weight %

Carbon - Max

Chromium

Nickel

Molybdenum

Titanium

304/304L

0.030

18.0 – 20.0

8.0 – 10.5

-

-

321

0.08

17.0 – 19.0

9.0 – 12.0

-

5 * C Min

316/316L

0.030

16.0 – 18.0

10.0 – 14.0

2.0 – 3.0

-

316Ti

0.08

16.0 – 18.0

10.0 – 14.0

2.0 – 3.0

5*C+N Min

The reason for the popularity of 316Ti in Europe is really an historical one. 316Ti exists as the preferred material in many specifications that have not been changed in years – it is basically Germany and the Eastern European countries that keep the grade alive. Regions to the west, south and north of Germany have since long changed to mainly using 316/316L for chemical process and aqueous corrosion applications.

DAVs ASME Sec VIII Div 1

500° F

850° F

1200° F

1500° F

316L

10.9

9.4

NP

NP

316

13.3

11.6

7.4

1.3

316Ti

13.2

11.7

7.4

1.3

316H

13.3

11.6

7.4

1.3

Although it can have a higher carbon content, there seems to be no mechanical property advantage to 316Ti since there is no difference in minimum yield stress for the three variations 316/1.4401, 316L/1.4404, 316Ti/1.4571 in any of the basic EN standards, EN 10088-2 (General application), EN 10088-4 (Structural application) and 10028-7 (Pressure vessel application). In all three Euronorms, the Rp0.2 (YS) is listed as minimum 220 MPa (32 KSI) for plate. In ASTM standards there is a slightly lower YS for 316L (25 KSI) versus 316 and 316Ti (30 KSI), but since nearly all 316L is dual certified as 316, there is no practical difference. The ASME Section VIII Design Allowable Values (DAV) for 316, 316H and 316Ti are the same all the way through the maximum permitted temperature of 1500° F. Note that this is due, in part, to the requirement that any austenitic stainless used at 1000° F or higher must have 0.04% minimum carbon.

In the final analysis, for typical aqueous corrosion applications, there is no advantage to 316Ti over dual certified 316/316L. For high temperature service (above 1000° F), there is no advantage in using 316Ti compared to 316H. There may be a few situations where equipment can see both elevated temperature service and occasional aqueous corrosion issues where a stabilized grade is warranted. Processes in the petroleum refining industry that can encounter these conditions include catalytic cracking and hyrdodesulfurization. In these areas, the corrosion resistance of 321 is adequate. If the anticipated aqueous corrosion is too severe for 321, it is more common to consider alloys like Alloy 20 or 825, which are much more readily available in North America.