Dished Head

Dished head(also called dished end,tank head,or vessel closure)is a curved,concave-shaped component that seals the open ends of cylindrical pressure vessels,tanks,boilers,reactors,and industrial containers.It is the most widely used end-closure type,engineered to withstand internal/external pressure while efficiently distributing stress across its surface.Dished heads replace flat heads to minimize stress concentrations,reduce required material thickness,and enhance structural safety.

Core Structure

A standard dished head(typically torispherical)consists of three key parts:

Crown(Central Dish):The main spherical or curved central section.

Knuckle(Toroidal Transition):The curved radius connecting the crown to the straight flange.

Straight Flange:A short cylindrical edge for welding to the vessel shell.

Common Types&Specifications

1.Torispherical Head(Flanged&Dished,F&D Head)

Geometry:Spherical crown+toroidal knuckle+straight flange.

Standard ASME Dimensions:Crown radius=vessel diameter(Ri=Di);knuckle radius=6%–10%of diameter(r=0.06Di or 0.1Di).

Pros:Low cost,easy to fabricate,shallow profile.

Cons:Higher stress concentration at knuckle.

Applications:Low-to-medium pressure vessels,storage tanks,atmospheric containers.

2.2:1 Ellipsoidal(Elliptical)Head

Geometry:Semi-ellipse with 2:1 axis ratio(major axis=2×minor axis).

Pros:Smooth stress distribution,stronger than torispherical heads,balanced cost and strength.

Applications:Mid-to-high pressure vessels,boilers,heat exchangers.

3.Hemispherical Head

Geometry:Half-sphere with uniform radius.

Pros:Optimal stress distribution,ideal pressure resistance,minimal thickness.

Cons:High fabrication cost,deep profile.

Applications:High-pressure reactors,gas storage,cryogenic tanks.

4.Conical Head

Geometry:Conical profile(with/without knuckle).

Pros:Improves material flow and drainage.

Applications:Hopper bottoms,silos,mixing vessels.

Materials

Carbon Steel:SA-516 Gr.60/70,Q245R,P265GH(general pressure service).

Stainless Steel:304,316L,321,904L(corrosive/hygienic applications).

Alloys:Alloy steel,titanium,nickel alloys(high-temperature/extreme corrosion).

Manufacturing Process

Forming:Hot/cold pressing,spinning,or forging.

Heat Treatment:Stress relieving post-forming.

Inspection:Dimensional checks,NDT(UT/RT/MT),pressure testing.

Finishing:Machining,bevelling,surface polishing.

Key Standards

ASME Section VIII(U.S.)

EN 13445(EU)

GB/T 25198(China)

DIN 28011/28013(Germany)

BS 5500(UK)

Advantages

Superior Pressure Resistance:Curved design distributes stress evenly vs.flat heads.

Cost Efficiency:Balances material usage and fabrication complexity.

Space Saving:Shallower profile than hemispherical heads.

Easy Installation:Straight flange simplifies welding to vessel shells.