Dished Heads

Torispherical heads (also referred to as klopper or korbbogen types) are formed from a spherical crown blended into a smaller knuckle radius at the straight flange. Elliptical heads, commonly 2:1, follow an approximately elliptical profile that gives a lower overall height for the same diameter and normally allows a thinner wall than a torispherical head at the same design pressure. Selection follows the design pressure, the available headroom and the code the vessel is designed to.

Diameter and thickness ranges are set per project rather than taken from a fixed list, and depend on the head type, the material grade and the forming method involved. Heavier walls and larger diameters may call for hot forming and, in some cases, petal or segmented construction. The workable range for a given case is confirmed against the drawing and the design conditions provided with the inquiry.

Heads are formed to the geometry and tolerance requirements of the governing design code, typically ASME Section VIII Division 1, EN 13445 or AD 2000 Merkblatt. In European practice DIN 28011 and DIN 28013 describe the torispherical and elliptical geometries, while EN 10028 and EN 10029 cover the plate material and its dimensional tolerances. The applicable set is confirmed with the vessel designer, since the code follows the vessel rather than the head on its own.

Material certification can be included where the project calls for it, most commonly EN 10204 type 3.1 certificates covering chemical composition and mechanical properties of the plate. Type 3.2 certification involving a third party or notified body inspector is possible where the design code or the end user specification requires it. Certification requirements should be stated with the inquiry, since they affect material selection at the plate stage.

Common grades include carbon steels such as P265GH and P355GH, low temperature steels such as P275NL2 and the 9% nickel grades used for cryogenic duty, and austenitic stainless steels including 304/304L and 316/316L. Aluminium alloys are used in some cryogenic and transport applications. Grade selection follows the design temperature, the medium and the code requirements rather than the head geometry itself.

Heads can be covered as standalone components for vessel builders working to their own drawings, or as one item within a wider equipment configuration. Both routes reference the same dimensional, material and code requirements. Which route applies is defined by the scope of the inquiry.