Effect of Ruthenium

Ruthenium additions to Titanium act essentially the same as palladium additions from both a metallurgical and corrosion standpoint. As fellow platinum group metals (PGM), ruthenium and palladium are both beta stabilizers in Titanium, and stabilize a very small volume fraction of second (beta) phase in alpha Titanium. Since these PGM additions are so minimal (<0.15 wt. %), these Pd and Ru alloy additions do not affect the basic metallurgy and mechanical and physical properties of the unalloyed Titanium base grade to which they are added. Therefore, these simple, lean Ti-Ru and Ti-Pd binary alloys will exhibit the same tensile and creep properties as their unalloyed Ti base alloys (i.e. Titanium Grades 2 and 1) and, hence, equivalent design allowable stress values as proposed (and as already accepted for all Ti-Pd alloys in the ASME Code). The fabricability of these alloys (forming, machining, welding) also remains the same.

Both palladium and ruthenium act in a similar manner to enhance Titanium corrosion resistance by providing sites of low hydrogen overvoltage that shift alloy potential in the noble (positive) direction, thereby stabilizing and maintaining the protective TiO₂ surface oxide film. This results in a substantial increase in corrosion resistance under mildly reducing acidic conditions, and when crevice corrosion in hot halide media (e.g. hot seawater, brines, chlorinated solutions, wet chlorine) is possible with unalloyed Titanium.

In general, Grade 26 , which corresponds to unalloyed Titanium Grade 2 for mechanical properties, will be the workhorse alloy used for process equipment applications such as shells, heads, tubesheets, tubing, etc.   Lower strength, higher ductility Grade 27, which corresponds to unalloyed Titanium Grade 1 for mechanical properties, will likely be utilized as a lining material (for loose lined and explosive clad vessels), for applications requiring better formability, and for some applications of welded tube and pipe. 

Welding Wire

Grade 26 or Grade 27 can be welded with either AWS 5.16-90, ER Ti-7 (Titanium-palladium grade) or with (proposed) ER Ti-27 (UNS Composition R52255, a matching ruthenium chemistry) and retain the same mechanical, physical, and enhanced corrosion resistant properties.

A Code Case request which will allow UNS R52255 Titanium-ruthenium welding wire to be in the F-52 Grouping along with the corresponding Titanium-palladium alloys has been submitted.

Cost

The cost for the ruthenium alloys is favorable compared to the palladium enhanced alloys, although recent volatility in precious metal prices has somewhat reduced the advantage of Ti Ru compared to the lean palladium alloys. The comparison below assumes the Titanium portion of each grade costs about the same as unalloyed Titanium and adds the value of the precious metal contained, allowing for 70% yield from ingot to mill product plate. These figures are approximately correct at July 1, 2000. .

Unfortunately, precious metal prices became quite volatile in early 2000, so costs relative to unalloyed grades have escalated sharply, the cost advantage of the ruthenium alloys compared to the palladium alloys is even greater.

ASME Code Status

Code Case 2235 was adopted by ASME on February 7, 2000. Copies of the Code Case are available from ASME in New York.

TABLE 1
CHEMICAL REQUIREMENTS

The Code Case references the ASTM Specifications for Grade 7 and 11, except with the chemistry shown in Table 1, so all product forms available in Grade 7 and 11 listed in Table 2 will be usable under the Code Case.

TABLE 2
PRODUCT SPECIFICATIONS

The Code Case also anchors the allowable stresses for Grade 26 to Titanium-palladium Grade 7 and for Grade 27 to Titanium-palladium Grade 11, so the stress values will be the same as for the corresponding Ti Pd Product Forms as listed in Table 3.

TABLE 3
MAXIMUM ALLOWABLE STRESS VALUES
(All Product Forms)*

* 0.85 reduction shall be made for weld efficiency in welded tube, pipe, and fittings.

Welding Procedures

Welding procedures utilizing standard techniques and the manual Gas Tungsten Arc process were qualified under Section IX, using welding wire identical to AWS 5.16-90 ER Ti-7, except for substitution of ruthenium for the palladium.  No difficulties were encountered. 

Use Titanium-Ruthenium Now

The Ti-0.1 Ru alloys can be used for ASME Code applications immediately. 

Titanium ruthenium alloys can be used for gasket surfaces to extend the range of operating conditions of unalloyed Titanium that might be subject to crevice corrosion.  Ti-0.1 Ru (Grade 27) can be specified for explosive clad or loose lined construction.  Ti-0.1 Ru can be used for internals and mechanical equipment.  Ti-0.1 Ru can be used for tubesheet lining and for tubing under some circumstances.

Users interested in the Ti-0.1 Ru alloy are encouraged to contact Titanium Fabrication Corporation for more detailed information on available product forms and pricing.