Titanium Sheet

• A Guide To Commercial Titanium Alloys And Their Forms
• Attractive Mechanical Properties
• Corrosion and Erosion Resistance
• Heat Transfer Characteristics

A Guide To Commercial Titanium Alloys And Their Forms

Attractive Mechanical Properties

The family of titanium alloys offers a wide spectrum of strength and combinations of strength and fracture toughness as shown in Figure 3. This permits optimized alloy selection which can be tailored for a critical component based on whether it is controlled by strength and S-N fatigue, or toughness and crack growth (i.e., critical flaw size) in service. Titanium alloys also exhibit excellent S-N fatigue strength and life in air, which remains relatively unaffected by seawater and other environments. Most titanium alloys can be processed to provide high fracture toughness with minimal environmental degradation (i.e., good SCC resistance) if required. In fact, the lower strength titanium alloys are generally resistant to stress corrosion cracking and corrosion-fatigue in aqueous chloride media.

For pressure-critical components and vessels for industrial applications, titanium alloys are qualified under numerous design codes and offer attractive design allowables up to 315°C (600°F).. Some common pressure design codes include the ASME Boiler and Pressure Vessel Code (Sections I, III, and VIII), the ANSI (ASME) B31.3 Pressure Code, the BS-5500, CODAP, Stoomwezen and Merkblatt European Codes, and the Australian AS 1210 and Japanese JIS codes.

• Exceptional erosion and erosion-corrosion resistance
• High fatigue strength in air and chloride environments
• High fracture toughness in air and chloride environments
• Low modulus of elasticity
• Low thermal expansion coefficient
• High melting point
• Essentially nonmagnetic
• High intrinsic shock resistance
• High ballistic resistance-to-density ratio
• Nontoxic, nonallergenic and fully biocompatible
• Very short radioactive half-life
• Excellent cryogenic properties

Corrosion and Erosion Resistance

Titanium alloys exhibit exceptional resistance to a vast range of chemical environments and conditions provided by a thin, invisible but extremely protective surface oxide film. This film, which is primarily TiO2, is highly tenacious, adherent, and chemically stable, and can spontaneously and instantaneously reheal itself if mechanically damaged if the least traces of oxygen or water (moisture) are present in the environment. This metal protection extends from mildly reducing to severely oxidizing, and from highly acidic to moderately alkaline environmental conditions; even at high temperatures. Titanium is especially known for its elevated resistance to localized attack and stress corrosion in aqueous chlorides (e.g., brines, seawater) and other halides and wet halogens (e.g., wet Cl2 or Cl2-sat. brines), and to hot, highly-oxidizing, acidic solutions (e.g., FeCl3 and nitric acid solutions) where most steels, stainless steels and copper- and nickel-based alloys can experience severe attack. Titanium alloys are also recognized for their superior resistance to erosion, erosion-corrosion, cavitation, and impingement in flowing, turbulent fluids. This exceptional wrought metal corrosion and erosion resistance can be expected in corresponding weldments, heat-affected zones and castings for most titanium alloys, since the same protective oxide surface film is formed.

The useful resistance of titanium alloys is limited in strong, highly-reducing acid media, such as moderately or highly concentrated solutions of HCl, HBr, H2SO4, and H3PO4, and in HF solutions at all concentrations, particularly as temperature increases. However, the presence of common background or contaminating oxidizing species (e.g., air, oxygen, ferrous alloy metallic corrosion products and other metallic ions and/or oxidizing compounds), even in concentrations as low as 20-100 ppm, can often maintain or dramatically extend the useful performance limits of titanium in dilute-to-moderate strength reducing acid media.

Where enhanced resistance to dilute reducing acids and/or crevice corrosion in hot (75°C) chloride/halide solutions is required, titanium alloys containing minor levels of palladium (Pd), ruthenium (Ru), nickel (Ni), and/or higher molybdenum (>3.5 wt.% Mo) should be considered. Some examples of these more corrosion-resistant titanium alloys include ASTM Grades 7, 11, 12, 16, 17, 18, 19, 20, 26, 27, 28, and 29. These minor alloy additions also inhibit susceptibility to stress corrosion cracking in high strength titanium alloys exposed to hot, sweet or sour brines.

Therefore, titanium alloys generally offer useful resistance to significantly larger ranges of chemical environments (i.e., pH and redox potential) and temperatures compared to steels, stainless steels and aluminum-, copper- and nickel-based alloys. Table 3 (see page 5) provides an overview of a myriad of chemical environments where titanium alloys have been successfully utilized in the chemical process and energy industries. More detailed corrosion data and application guidelines for utilizing and testing titanium alloys in these and other environments can be found in the reference section in the back of this booklet.

Heat Transfer Characteristics

Titanium has been a very attractive and well-established heat transfer material in shell/tube, plate/frame, and other types of heat exchangers for process fluid heating or cooling, especially in seawater coolers. Exchanger heat transfer efficiency can be optimized because of the following beneficial attributes of titanium:

• Exceptional resistance to corrosion and fluid erosion
• An extremely thin, conductive oxide surface film
• A hard, smooth, difficult-to-adhere-to surface
• A surface that promotes condensation
• Reasonably good thermal conductivity
• Good strength

Although unalloyed titanium possesses an inherent thermal conductivity below that of copper or aluminum, its conductivity is still approximately 10-20% higher than typical stainless steel alloys. With its good strength and ability to fully withstand corrosion and erosion from flowing, turbulent fluids (i.e., zero corrosion allowance), titanium walls can be thinned down dramatically to minimize heat transfer resistance (and cost). Titanium's smooth, non-corroding, hard-to-adhere to surfaces maintains high cleanliness factors over time. This surface promotes drop-wise condensation from aqueous vapors, thereby enhancing condensation rates in cooler/condensers compared to other metals as indicated in Figure 6. The ability to design and operate with high process or cooling water side flow rates and/or turbulence further enhances overall heat transfer efficiency.

All of these attributes permit titanium heat exchanger size, material requirements and overall initial life cycle costs to be reduced, making titanium heat exchangers more efficient and cost-effective than those designed with other common engineering alloys.

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