blog about Guide to Pressure Vessel Head Selection Shapes Materials Uses

Pressure vessels are indispensable components in modern industrial systems, widely used in petroleum refining, energy production, pharmaceuticals, food processing, and numerous other sectors. These critical containers play vital roles in storing, transporting, and processing various media. However, the immense internal pressures they withstand create potential hazards—any failure could lead to catastrophic accidents resulting in casualties and significant property damage. Therefore, ensuring the safe and reliable operation of pressure vessels is paramount.

The vessel head, serving as the pressure vessel's end closure component, performs essential functions including sealing the container, withstanding pressure, and facilitating pipeline connections. Much like a pressure cooker's lid, the head must reliably contain internal pressures, prevent media leakage, and maintain structural integrity. This report provides comprehensive technical guidance for pressure vessel designers, thoroughly analyzing various head types, their characteristics, application scenarios, and selection criteria to support informed decision-making that enhances both safety and efficiency.

Pressure vessel heads, also called end closures or domes, are components that seal the ends of cylindrical or spherical pressure vessels. They typically form the top and bottom closures (for vertical vessels) or connect to piping and other equipment. Primary functions include:

• Container sealing: Effectively seals the pressure vessel to prevent media leakage.
• Pressure containment: Withstands internal pressures and transfers loads to the vessel walls.
• Pipeline connections: Facilitates connections to piping systems for media transfer and processing.
• Structural support: Provides stability and support for vertical vessel configurations.

Heads are categorized by shape, manufacturing process, and material composition.

• Spherical heads: Ideal geometry with uniform stress distribution across the material.
• Ellipsoidal heads: Cost-effective option with height typically much smaller than diameter.
• Torispherical heads: Feature fixed crown radius determined by head type.
• Flat heads: Comprise flat plates connected by toroidal knuckle transitions.
• Reverse torispherical heads: Inverted torispherical configuration.
• Conical heads: Tapered conical geometry.

• Monolithic heads: Formed from single material pieces.
• Segmented heads: Fabricated by welding multiple sections.

• Carbon steel: Excellent strength and weldability for non-corrosive media.
• Stainless steel: Superior corrosion resistance for aggressive media.
• Alloy steel: Enhanced strength and high-temperature performance.
• Aluminum: Lightweight with good corrosion resistance.

Head fabrication typically involves two primary stages:

• Press forming: Raw materials (steel plates, stainless sheets) are pressed using dies to create curved dished or spherical shapes.
• Edge treatment: Formed heads undergo edge trimming, flanging, or welding preparation for vessel attachment.

Large or complex heads may require segmented construction with welded joints.

Characteristics:

• Uniform stress distribution maximizes material strength utilization
• Exceptional pressure containment capability
• High material efficiency reduces costs

Applications: High-pressure vessels, storage tanks, reactors—particularly for extreme pressure/temperature conditions. Examples include nuclear reactor pressure vessels, deep-sea submersibles, and high-pressure gas storage.

Characteristics:

• Cost-effective with shallow depth-to-diameter ratio
• Balanced strength between spherical and torispherical designs
• Optimal space utilization

Applications: Storage tanks (petroleum, chemicals), reactors (chemical, pharmaceutical), heat exchangers (steam, cooling systems).

Types:

• ASME Torispherical: Crown radius equals external diameter (r1 = Do); knuckle radius 6% of diameter (r2 = 0.06Do)
• Standard 80/10: Crown radius equals diameter (r1 = Do); knuckle radius 10% (r2 = 0.1Do)
• DIN 28013 (80%): Crown radius 80% of diameter (r1 = 0.8Do); knuckle radius 15.4% (r2 = 0.154Do)

Applications: Similar to ellipsoidal heads in storage, reactors, and heat exchange systems.

Critical factors for material selection include:

• Operating pressure and temperature requirements
• Media corrosiveness
• Material strength and ductility
• Weldability
• Cost considerations

• Carbon steels (Q235, Q345): General-purpose applications
• Stainless steels (304, 316L): Corrosive environments
• Alloy steels (16MnR, 15CrMoR): High-temperature/pressure service
• Aluminum alloys (5052, 6061): Lightweight requirements
• Titanium alloys: Extreme conditions

Cold-formed heads may require stress-relieving heat treatments, while hot-formed heads typically do not.

Purposes:

• Residual stress relief
• Mechanical property enhancement
• Grain refinement

Methods: Annealing, normalizing, tempering—selected based on material and service requirements.

Key considerations for head selection:

• Compliance with design codes (ASME, EN, etc.)
• Operating conditions (pressure, temperature, media)
• Head geometry optimization
• Material compatibility
• Dimensional matching
• Cost-effectiveness

Quality assurance protocols include:

• Visual and dimensional inspections
• Material verification
• Hydrostatic/pneumatic pressure testing
• Non-destructive examination (UT, RT)

Essential maintenance includes:

• Regular visual inspections
• Surface cleaning
• Connection lubrication
• Timely replacement of compromised components

Emerging developments include:

• Advanced material applications
• Computational design optimization (CAD/FEA)
• Automated manufacturing techniques
• Environmentally sustainable practices