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Sells Dished Heads
Buys Cold Rolled, Tubes-Pipes Seamless
Buys Cold Rolled, Tubes-Pipes Seamless
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Formed stainless steel ends that close the shell of a tank, pressure vessel, reactor or silo. The shapes and dimensions are the same as carbon steel heads; what is different is the grade, the surface — pickled, passivated, ground or polished — and, for food and pharmaceutical vessels, a hygienic finish inside.
A dished head is pressed or spun from a circular blank of plate into a shallow dome with a curved 'knuckle' and a short straight flange that is welded to the vessel shell. The deeper the dome, the better it carries pressure: a hemispherical head is the strongest and most expensive to form, a 2:1 ellipsoidal (semi-elliptical) head is the usual choice for pressure vessels, and a torispherical head — a large crown radius joined to a small knuckle — is the cheapest and most common for low-pressure and atmospheric tanks.
The geometry, the series of standard sizes and the design rules are the same for carbon and stainless heads, and are not repeated here: see the dished head dimensions on the carbon steel page, which apply equally to stainless heads. Stainless heads add their own concerns. Cold forming work-hardens austenitic plate, and design codes set strain limits beyond which a solution anneal is needed; duplex is stronger and springs back more, so it needs more press force and careful heat treatment; and every head must leave the shop free of iron contamination, weld heat tint and scale.
After forming, stainless heads are cleaned and passivated (ASTM A380 and A967 describe the methods): pickling paste or bath removes the oxide and embedded iron, and the chromium oxide film then reforms. Heads for food, beverage and pharmaceutical vessels are ground and polished inside, typically to 0.8 µm Ra or better, and sometimes electropolished; ASME BPE sets the finish classes used in biopharma, and the knuckle must be smooth and fully drainable.
In the GCC, stainless heads are used by tank and vessel fabricators serving desalination and water treatment, dairy and juice plants, chemical and petrochemical plants and the oil and gas sector. Heads are pressed by regional fabricators for common sizes and imported from specialist head makers in Europe, India and China for large diameters, thick duplex and hygienic polished ends.
A head is ordered by type, inside or outside diameter, nominal and minimum thickness after forming, straight flange length, grade and finish. The thickness thins at the knuckle during forming, so a minimum thickness after forming must be stated when the head is designed to a code.
| Region | Standard | What it covers |
|---|---|---|
| Germany | DIN 28011 DIN |
Torispherical heads (Klöpperboden) — dimensions |
| Germany | DIN 28013 DIN |
Semi-ellipsoidal heads (Korbbogenboden) — dimensions |
| Europe | EN 13445 CEN-CENELEC |
Unfired pressure vessels — design, materials and fabrication rules, including forming and heat treatment of heads |
| USA | ASME BPVC Section VIII Division 1 ASME |
Rules for construction of pressure vessels — design rules for ellipsoidal, torispherical and hemispherical heads |
| USA | ASME BPE ASME |
Bioprocessing equipment — surface finish and drainability for pharmaceutical vessels and heads |
| USA | ASTM A240/A240M ASTM |
Chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels and general applications |
| Europe | EN 10028-7 CEN-CENELEC |
Flat products made of steels for pressure purposes — stainless steels |
| USA | ASTM A380/A380M ASTM |
Cleaning, descaling and passivation of stainless steel parts, equipment and systems |
| USA | ASTM A967/A967M ASTM |
Chemical passivation treatments for stainless steel parts |
Grade equivalents and the standards bodies: Steel grades & standards
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