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Views: 0 Author: Site Editor Publish Time: 2026-08-25 Origin: Site
Pressure vessel heads—also known as tank ends or dished heads—are critical pressure-retaining closures used in industrial boilers, chemical reactors, oil and gas storage tanks, pharmaceutical vessels, and cryogenic containers. Metal spinning, often combined with cold or hot dishing, provides a highly efficient, seamless method for forming thick-plate circular metal blanks into heavy-duty hemispherical, ellipsoidal, and torispherical profiles. Spinning produces a uniform, seamless structure with enhanced grain flow alignment and high structural integrity, eliminating the longitudinal weld seams inherent in segmented fabrication. As a specialized OEM manufacturer, we design and produce pressure vessel heads that comply strictly with international pressure vessel codes, including ASME Section VIII Division 1 and 2, PED 2014/68/EU, and GB 150.
Different dished head profiles offer unique balances between pressure-containment capability, internal fluid volume, and manufacturing complexity.
Geometry: Major-to-minor axis ratio of 2:1, providing an optimal stress distribution profile under internal fluid pressure.
Code Standard: The standard shape for medium- to high-pressure storage tanks under ASME Boiler and Pressure Vessel Code (BPVC).
Pressure Efficiency: Wall thickness required is approximately equal to that of a seamless cylindrical shell of the same diameter and design pressure.
Geometry: Composed of a central spherical dish region tied to a cylindrical straight flange via a toroidal knuckle radius.
Application: Widely used in low- to medium-pressure storage vessels, food processing tanks, and atmospheric silos.
Formability: Easier to spin and shape than deep ellipsoidal profiles, resulting in lower manufacturing tooling costs for large diameters.
Geometry: Pure half-sphere profile offering the highest theoretical pressure containment for a given wall thickness.
Application: Extreme pressure applications, high-pressure gas storage spheres, and deep-sea submersible hulls.
Thickness Advantage: Requires approximately half the wall thickness of a torispherical head operating under identical design pressure, reducing overall material weight.
Geometry: Conical transitions with spun knuckle radii or flat bottom discs featuring formed perimeter lips.
Application: Bottom hopper outlets, conical settlers, and atmospheric process tanks requiring easy gravity drainage.
Forming heavy plate into dished heads depends on plate thickness, material ductility, and machine tonnage capacity.
Process executed at room temperature using high-tonnage hydraulic dishing presses followed by heavy-duty CNC crown-and-flange spinning machines.
Typically used for carbon steel up to 25 mm and stainless steel up to 20 mm, depending on diameter.
Cold working increases yield strength and ultimate tensile strength through strain hardening, though it slightly reduces elongation.
Produces clean, oxide-free surfaces requiring minimal post-forming scale removal.
The circular blank is preheated in a gas-fired furnace to the material's forging temperature range (typically 900°C to 1150°C for carbon steels) before high-speed dishing and spinning.
Required for heavy wall plates (exceeding 25 mm up to 100 mm or more) and large diameters exceeding 4000 mm.
Drastically reduces required machine roller forces and eliminates internal stress cracking in low-ductility or heavy alloy steels.
Requires mechanical shot blasting or acid pickling to remove furnace scale before non-destructive testing.
Pressure vessel materials must balance high tensile strength, notch toughness, weldability, and resistance to chemical corrosion or hydrogen embrittlement.
SA-516 Grade 60 / 70, SA-285 Grade C, P265GH, P355GH.
SA-516 Gr. 70 is the industry standard for moderate- and lower-temperature pressure vessel applications, offering superior notch toughness and formability.
SA-240 Type 304/304L, 316/316L, 2205 Duplex Stainless Steel.
Outstanding corrosion resistance for pharmaceutical, food processing, and chemical processing tanks. Duplex grades provide double the yield strength of standard austenitic grades, enabling thinner, lighter head designs.
Nickel alloys (Inconel, Monel, Hastelloy), Titanium Grade 2, and Aluminum alloys (5083 / 6061).
Specified for extreme chemical environments, offshore desalination, and cryogenic LNG storage vessels.
Ensuring compliance with ASME Section VIII Division 1 rules requires addressing forming tolerances, wall thinning allowances, and post-forming heat treatment.
During the dishing and flanging operations, the material undergoes localized stretching, primarily in the knuckle zone.
Out-of-roundness (difference between maximum and minimum inside diameters) must not exceed 1% of the nominal diameter.
The internal or external profile must conform smoothly to the specified shape, with local crown-to-knuckle deviations held within ASME Code limits to avoid localized stress peaks under pressure.
Carbon steel heads formed by cold spinning may require Post-Weld / Post-Forming Heat Treatment (PWHT) if the cold strain exceeds code thresholds (typically 5% strain according to ASME UCS-79).
Stainless steel dished heads subjected to cold forming are often solution annealed at 1050°C followed by rapid water quenching to restore full corrosion resistance and eliminate work-hardened stresses.
Because pressure vessel heads operate under dangerous internal pressure, strict inspection protocols verify structural integrity prior to vessel assembly.
Checks starting plate raw material and finished heads for internal laminations, inclusions, and wall thickness uniformity across the crown and knuckle.
Conducted on central blank weld seams (if the starting circular plate was constructed from two welded sheets) prior to and after spinning.
Inspects the high-stress knuckle region and trimmed edge profiles for surface micro-cracks caused by forming strain.
Laser profiling verifies crown radius, knuckle radius, straight flange length, and overall dish depth against approved engineering drawings.
Seamless pressure vessel head spinning combines advanced heavy-plate metal forming with strict mechanical engineering standards. By optimizing head geometry, selecting the appropriate cold or hot forming process, accounting for wall thinning, and completing full NDT inspection, manufacturers provide safe, code-compliant dished heads for critical energy, chemical, and industrial applications worldwide.
