Dished ends – find manufacturers and suppliers

Dished ends are curved metal components that serve as a pressure-resistant closure for containers and boilers and are one of the most frequently used bottom shapes in pressure vessel construction due to their good stress distribution.

Dished ends are curved, egg-shaped ends of pressure vessels, tanks and pipelines that belong to the family of curved molded ends. The shape was invented by Georg Kloppsch (1874-1951).

Below you will find the mode of operation, characteristic shapes, the manufacture of dished ends, their use, their advantages and their limitations:

How dished ends work:

The central task of a dished end is to safely absorb and dissipate compressive forces.

1. Stress distribution:
   The curvature distributes the stress in the floor more evenly. The spherical cap absorbs the main forces, while the transition arch creates a gentle flow of force to the cylindrical shell.
2. Avoidance of stress peaks:
   The rounding between the spherical segment and the cylinder reduces stress concentrations that could otherwise lead to material fatigue or breakage.
3. Strength:
   Dished ends are stronger than flat or conical ends for the same amount of material. They can therefore be designed for higher pressures.
4. Efficiency:
   Thanks to the shape, wall thicknesses and weight can be reduced without compromising safety.

Characteristic shapes of dished ends:

The characteristic shape of dished ends with three zones is therefore the result of mechanical and manufacturing requirements for pressure-bearing components. The zones are:

1. The spherical segment (calotte) as the curved middle section.
2. The transition bend (torus radius) as the connection between the spherical segment and the cylinder.
3. A cylindrical attachment (straight edge) for the connection to the cylinder of the container.

This shape ensures a more even distribution of stress under pressure load than with flat heads.

Manufacture of dished ends:

Dished ends are usually cold or hot formed. Large dished ends are often hot-pressed or forged, smaller ones can also be cold-pressed. They are then mechanically processed (e.g. trimmed) and often heat-treated to relieve stresses.

Use of dished ends:

Dished ends are widely used in the pressure vessel and apparatus engineering industry. Typical applications are:

1. Pressure vessels:
Chemical industry, petrochemical industry, food technology - wherever pressure vessels are required.

2. Storage tanks:
Especially for liquids and gases under pressure.

3. Boilers and heat exchangers:
For vessels that are under overpressure or have to withstand high temperatures.

4. Pipes with end caps:
Pipe systems that need to be sealed at the ends.

5. Autoclaves and reactors:
In the chemical and pharmaceutical industries where pressure and temperature need to be controlled.

6. Boiler construction:
In power plant construction, where steam pressure vessels need to be securely sealed.

Advantages of dished ends:

• High mechanical strength
• Favorable stress distribution
• Weight saving compared to flat heads at the same pressure
• Cost-efficient production for series production
• Simple connection to cylinder segments

Limits of dished heads:

• More complex to manufacture than simple flat heads
• More expensive than conical heads in certain size ranges
• At extremely high pressure, alternative shapes such as hemispherical heads can be even more advantageous

Dished ends are curved bottom shapes for pressure vessels that offer ideal stress distribution under internal pressure thanks to their shape. They combine good mechanical properties with economical production. Their most important function is to safely absorb the internal pressure and dissipate it into the cylindrical vessel shell. They are used wherever pressure vessels, tanks or pipes need to be securely sealed - especially in the chemical industry, power plant construction and food technology.

Below you will find an overview of the most important criteria that you should pay attention to when purchasing dished ends:

The purchase of dished ends requires precise technical specifications and a clear understanding of the application conditions. The selection of the right material, compliance with relevant standards and approvals, careful definition of the geometry and pressure requirements and precise welding preparation are crucial.

• The choice of material is one of the most important points. Dished ends are manufactured from various steels such as carbon steel, stainless steel, alloy steels or aluminum. The decisive factors are:
• Corrosion resistance - depending on the medium and operating environment.
• Pressure and temperature resistance - e.g. for steam applications or low-temperature tanks
• Weldability - the base often has to be welded to a jacket
• Conformity to standards - e.g. EN 10028 (flat products for pressure vessels) or ASME/ASTM standards
• The material must be suitable for the medium, process and regulations. Buyers should always clarify which approvals or test certificates are required.
• Professional procurement requires clarification of applicable standards:
• EN 13445 for pressurized unfired containers in Europe.
• AD 2000 German regulations for pressure vessels and piping.
• ASME Section VIII is a section of the ASME Boiler & Pressure Vessel Code (BPVC) that deals with pressure vessels.
• PED (Pressure Equipment Directive), Directive 2014/68/EU for EU-compliant pressure equipment.
• The heads must be manufactured, tested and documented in accordance with the relevant standard. An acceptance test certificate in accordance with EN 10204 is often required here, e.g. 3.1 or 3.2.
• Important parameters for geometry and dimensions are
• Inner diameter
• Wall thickness (nominal thickness)
• Height and calotte radius
• Transition bend (torus radius)
• Straight shoulder (weld edge length)
• The dimensions must match the casing pipes or tanks. Manufacturing tolerances must also be specified. Tight tolerances often apply to pressure vessels in accordance with the standard.
• Dished ends are calculated for certain pressure levels. This must be clarified when purchasing:
• Design pressure
• Operating temperature range
• Safety coefficient (in accordance with standard specifications)
• The supplier requires this data for design and verification purposes.
• The heads can be hot or cold formed. Hot forming is used for thicker heads (high pressures) or large diameters. Points that should be specified when purchasing:
• Forming process (hot/cold)
• Post-processing such as heat treatment
• Final machining
• Deburring and surface finish
• Sometimes solution annealing or normalizing is prescribed to eliminate forming stresses.
• For welding preparation, it is necessary to clarify how the approach should be executed. Please note
• Weld edge length
• Chamfer or blunt
• Weld seam preparation according to standard
• This influences assembly costs and weldability. Suppliers can offer different standard joints.
• For hygienic or corrosion-critical applications, e.g. food, pharmaceuticals, the surface can be decisive:
• Roughness specifications (e.g. Ra values)
• Pickling, passivation, polishing
• Coatings or paintwork
• These requirements should be specified precisely in the inquiry.
• Pressure vessels are subject to high safety requirements. Buyers must clarify:
• Material certificates (EN 10204 3.1/3.2)
• Dimensional inspection reports
• Ultrasonic testing, X-ray inspection
• Visual inspection
• Acceptance by independent inspectors (e.g. TÜV, Notified Body)
• The desired scope of testing should be specified in the contract.
• Dished heads are often large and heavy. Important points for delivery conditions and logistics are
• Packaging - protection against corrosion and damage
• Transportation - truck, container, crane logistics
• Delivery time - large dished ends often have long production times
• Incoterms - e.g. EXW, FOB, DAP
• Insurance and customs formalities are also relevant for international procurement.

When purchasing dished ends, it is important to keep an eye on the surface requirements and the scope of testing in order to guarantee safety and quality in subsequent operation. Logistical aspects such as packaging, transportation and delivery conditions should also be clarified at an early stage. An experienced, certified supplier with transparent processes and complete documentation is essential. Ultimately, the more precise and complete the requirements are defined in advance, the smoother and safer the procurement process will be - and the better quality, cost control and operational reliability can be guaranteed in the long term.

Dished ends can be sourced from various suppliers. You will find comprehensive information on manufacturers and suppliers of Dished ends around the world on Exportpages.