Design Guide for Titanium Pressure Vessels

Titanium pressure vessels are widely used in industries such as chemical processing, petroleum, and pharmaceuticals due to their exceptional corrosion resistance, high strength, and lightweight properties. However, the unique characteristics of titanium require adherence to specific design and manufacturing guidelines to ensure optimal performance, cost-effectiveness, and long-term stability. Below is a comprehensive guide for designing titanium pressure vessels.

Design Structure and Welding Requirements

 
The design of titanium pressure vessels should focus on structural simplicity and welding quality to facilitate cleaning and maintenance while meeting the unique welding requirements of titanium. Proper design and welding methods will directly impact the vessel's performance and durability.

1. Structural Simplicity

 
The design of titanium pressure vessels should be as simple as possible to facilitate the cleaning of weld seams and surrounding surfaces. Complex structures should be avoided to ensure that inert gas shields can effectively protect welds and their heat-affected zones during welding, preventing contamination or damage.

2. Welding Requirements

 
Titanium and its alloys can be welded to each other but cannot be fusion-welded with other metals. When joining with other metals is necessary, methods such as adhesive bonding, brazing, explosive welding, or bolting can be used. To ensure high welding quality, inert gas shielded welding is recommended to minimize oxidation and contamination.

Characteristics and Processing of Titanium

 
Titanium's unique physical properties significantly impact its processing methods. Understanding titanium's cold creep, impact toughness, and work hardening characteristics helps optimize design and processing techniques to ensure vessel reliability and durability.

1. Cold Creep Characteristics

 
Titanium materials exhibit significant cold creep, necessitating the avoidance of high-stress areas in the design. Cold creep can cause material shape changes under long-term loads, so this characteristic should be considered during the design phase to ensure the vessel maintains stable shape during use.

2. Impact Toughness

 
Titanium has low impact toughness, requiring the avoidance of stress concentrations in structural designs. Weld joints should be designed for smooth transitions to minimize stress concentrations that could lead to cracks or failures. Additionally, the design should ensure structural continuity to enhance overall toughness and durability.

3. Plastic Deformation and Work Hardening

 
Titanium materials have a narrow range of plastic deformation and are prone to work hardening during processing. Therefore, larger bending radii are recommended during bending and flanging operations to prevent material cracking. During expansion processes, smaller expansion ratios should be used to reduce the risk of material deformation.

Handling Corrosive Media

 
Titanium's excellent corrosion resistance is crucial when handling corrosive media. Special attention should be given to avoiding crevice corrosion and erosion corrosion to ensure long-term stability and reliability of the equipment.

1. Crevice Corrosion

 
Titanium materials can be susceptible to crevice corrosion in certain media. When designing equipment for these media, avoid gaps and stagnation areas. Welding can be used instead of bolted, riveted, or adhesive connections to reduce the risk of crevice corrosion. Additionally, titanium alloys or coatings resistant to crevice corrosion can be used at flange connections to enhance corrosion resistance.

2. Electrically Conductive Corrosive Media

For equipment handling electrically conductive corrosive media, consider the contact between titanium and other metals. Assess titanium's suitability for contact with other metals based on the media's electrochemical properties, material electrode potentials, anode-to-cathode area ratios, and potential hydrogen absorption. If contact with other metals is unavoidable, protective measures such as using a third material as a transition layer or employing sacrificial anodes should be implemented to reduce corrosion risk.

3. Erosion Corrosion and Flow Control

 
Titanium is prone to erosion corrosion and impact corrosion in high-velocity or rapidly changing flow media. Design systems with low flow velocities and avoid sudden changes in flow speed or direction. Protective baffles or sleeves can be installed in areas prone to erosion corrosion and impact corrosion to safeguard the material.

Economics and Material Usage

 
The high cost of titanium necessitates careful consideration of cost-effectiveness and material optimization in design. Properly selecting titanium application areas and combining with other cost-effective materials can significantly reduce overall costs.

1. Cost of Titanium

 
Titanium is typically more than three times the cost of stainless steel, so it should be used judiciously in the design of titanium equipment. Titanium should be primarily used in areas that come into contact with corrosive media, while supporting components and non-corrosive parts can be made from less expensive carbon steel. External supports (such as skirt-type, saddle-type, suspended, and leg-type) as well as flanges and flange covers should be made of carbon steel to lower overall costs.

2. Wall Thickness and Material Selection

 
For pressure vessels with wall thicknesses exceeding 12mm, titanium-lined copper vessels or titanium-steel composite plates can be used. This approach effectively controls costs while maintaining good corrosion resistance. Titanium-lined vessels provide excellent corrosion resistance in the core area, while composite plates ensure strength and reduce titanium usage.

Flange and Cover Design

 
In titanium pressure vessels, the design of flanges and covers affects overall strength, sealing performance, and cost control. Selecting appropriate flange types and cover materials can ensure performance while reducing costs.

1. Flange Design

 
For all-titanium pressure vessels, flanges and connection flanges typically use loose flanges, unless the connection port structure is complex or the nominal diameter is less than 25mm. Loose flanges effectively save titanium material and reduce equipment costs. However, plate-type loose flanges are generally suitable for pressures up to 1.6MPa. Flat-weld ring loose flanges are unsuitable for environments with severe pressure or temperature fluctuations, whereas flanged ring types are suitable for such environments.

2. Cover Design

 
For all-titanium pressure vessels, flat covers, manholes, handholes, and flange covers usually use titanium-lined steel covers or titanium-steel composite covers. This design ensures corrosion resistance while effectively lowering equipment costs. Using titanium-steel composite materials retains the excellent performance of titanium while reducing the amount of titanium used, thereby lowering overall costs.

Conclusion

 
Designing titanium pressure vessels requires a comprehensive consideration of titanium's characteristics, operating environment, and cost-effectiveness. Through precise design and material selection, the advantages of titanium can be fully utilized while effectively controlling manufacturing and operational costs. Adhering to the design principles outlined above will ensure that titanium pressure vessels meet high-performance requirements while maintaining cost-effectiveness and long-term stability.