Stainless Steel Elliptical Head
Stainless Steel Elliptical Head Manufacturer
Stainless steel elliptical heads, also called ellipsoidal heads or elliptical dished ends, are formed vessel ends used on pressure vessels, tanks, reactors and process equipment.
The common 2:1 ellipsoidal head is based on an ellipse whose full major axis is twice its full minor axis. For an ideal 2:1 geometry, the internal crown depth from tangent line to apex is approximately one-quarter of the inside diameter, excluding the straight flange.
Stainless Steel Elliptical Head: Quick Specifications
| Specification Item | LYH Published / Project Capability | What the Buyer Should Define |
|---|---|---|
| Head Type | Elliptical / ellipsoidal head | 2:1 geometry or project-specific geometry |
| Diameter | 100–6000 mm published range | State whether dimension is ID, OD or vessel-shell basis |
| Thickness | 3–150 mm published range | State starting plate thickness and/or required minimum finished thickness |
| Common Stainless Grades | 304, 316L | Exact ASTM / ASME / EN grade and specification |
| Other Stainless Grades | Subject to material and forming feasibility | 304L, 316, 321, 316Ti, duplex or project grade as applicable |
| Forming | Hot pressing, cold pressing, cold spinning | Process may depend on diameter, material and thickness |
| Straight Flange | Custom by drawing / feasibility | Required straight length and final diameter |
| Edge Preparation | Plain, bevel or project requirement | Bevel angle, root face and weld-joint detail |
| Head-to-Shell Connection | Normally prepared for welded assembly | Approved shell-to-head weld detail |
| Inspection | By PO / project requirement | MTC, dimensions, PT, UT/RT, PMI or third-party inspection when required |
2:1 Ellipsoidal Head Dimensions
A true 2:1 ellipsoidal head is generated from half of an ellipse. The full ellipse has a major axis twice its minor axis.
If Di is the head inside diameter at the tangent line / straight-flange region, the theoretical inside crown depth of an ideal 2:1 head is:
| Inside Diameter Di | Theoretical Crown Depth hi | Plus |
|---|---|---|
| 1000 mm | 250 mm | Specified straight flange |
| 2000 mm | 500 mm | Specified straight flange |
| 3000 mm | 750 mm | Specified straight flange |
| 4000 mm | 1000 mm | Specified straight flange |
| 6000 mm | 1500 mm | Specified straight flange |
Dimensions to Put on an Elliptical Head Drawing
Diameter
State clearly whether the project controls inside diameter (ID), outside diameter (OD) or finished shell-fit diameter.
Crown Depth
For ideal 2:1 geometry, inside crown depth is approximately ID / 4, excluding straight flange.
Straight Flange
Specify the cylindrical straight length between the tangent region and trimmed edge.
Finished Thickness
Define required minimum thickness after forming, especially where thinning is design-critical.
Edge Preparation
Specify plain edge, bevel geometry, root face and final trim dimensions.
Tolerance
Define dimensional tolerances using the governing code, approved drawing and project specification.
Ellipsoidal vs Hemispherical vs Torispherical Head
These head types should not be compared using a universal percentage such as “half the material” or “90% of the strength.” Pressure design depends on geometry, diameter, material, allowable stress, joint efficiency, thickness and the applicable code.
| Head Type | Geometry | General Engineering Characteristic | Procurement Consideration |
|---|---|---|---|
| 2:1 Ellipsoidal | Semi-ellipsoidal profile | Common balance between depth, pressure efficiency and fabrication | Widely used for pressure vessels and tanks |
| Hemispherical | Half sphere | Structurally efficient pressure geometry | Greater depth and more demanding fabrication |
| Torispherical / F&D | Spherical crown plus toroidal knuckle | Shallower geometry with different stress distribution | Often selected where fabrication depth / cost matters |
Stainless Steel Grades for Elliptical Heads
Material selection should follow corrosion environment, forming requirements, welding, operating temperature and the pressure-vessel code.
| Grade | Typical Reason to Evaluate It | Forming / Procurement Note |
|---|---|---|
| 304 / 304L | General stainless pressure-vessel and tank service | 304L is often preferred when extensive welding is involved |
| 316 / 316L | Higher chloride / process-corrosion margin than 304 family | 316L is widely used for welded process and sanitary equipment |
| 321 / 316Ti | Stabilized grades for specific thermal-service requirements | Confirm forming route, heat treatment and code requirement |
| 2205 Duplex | Higher strength and chloride resistance where justified | Requires material-specific forming and fabrication control |
| Other Stainless / Alloy | Special corrosion or temperature service | Subject to material availability and forming feasibility |
Grade references: 304 , 304L , 316L , 321 and 2205 Duplex .
Material & Pressure Vessel Standards
The material specification and the pressure-vessel construction code perform different functions.
ASTM A240 / ASME Material Specification
ASTM A240/A240M covers chromium, chromium-nickel and related stainless plate, sheet and strip for pressure-vessel and general applications.
Use the project-required ASTM / ASME material specification and exact grade designation.
ASME BPVC Section VIII
ASME Section VIII provides pressure-vessel construction rules covering design, fabrication, inspection, testing and certification.
The purchaser should specify the required Division, edition, code stamp / certification scope and inspection requirements where applicable.
Manufacturing: Pressing, Spinning & Forming
Cold Pressing
Suitable for selected combinations of diameter, thickness and stainless grade.
Cold work, springback and local thinning must be considered.
Hot Pressing
May be selected for heavier sections or forming conditions where hot forming improves manufacturability.
Heat treatment and final material condition must follow the applicable specification.
Spinning
Rotary forming can be suitable for selected diameters, thicknesses and production requirements.
Final geometry and minimum wall thickness still require inspection.
Seamless Forming, Welded Blanks & Large-Diameter Heads
A head can be formed from a single plate blank when plate size and forming capacity permit.
For larger diameters, thicker sections or restricted plate widths, the manufacturing route may require a welded blank or another approved fabrication method before forming.
If the head contains a weld seam, the purchase specification should define joint category, welding procedure, required NDE, joint efficiency where applicable, traceability and acceptance criteria under the governing code.
Straight Flange & Weld Edge Preparation
The straight flange is the cylindrical section between the ellipsoidal tangent region and the trimmed edge.
It provides geometry for fit-up to the vessel shell and should be stated explicitly on the approved drawing.
| RFQ Dimension | Why It Matters |
|---|---|
| Straight Flange Length | Controls shell fit-up and total head height |
| Finished Diameter | Must match shell fabrication basis and tolerance |
| Bevel Angle | Part of the shell-to-head weld preparation |
| Root Face / Land | Must match the qualified welding detail |
| Edge Squareness | Affects fit-up and weld consistency |
Elliptical Head Inspection & Quality Control
Inspection scope should be agreed before production, especially for code pressure-vessel work.
| Inspection Item | Typical Check | When Required |
|---|---|---|
| Material Traceability | Heat number and MTC correlation | As required by PO / code |
| PMI | Alloy verification | When specified |
| Diameter | ID / OD / circumference | Each project drawing |
| Head Depth | Tangent line to apex / total height | Dimensional inspection |
| Minimum Thickness | UT thickness mapping or agreed method | Where required after forming |
| Surface Examination | Visual and PT where specified | Project / code dependent |
| Weld NDE | RT / UT / PT as applicable | For welded construction when required |
| Bevel / Edge | Angle, root face and dimensional fit | Before shipment |
See: Quality Inspection .
Surface Condition for Stainless Elliptical Heads
Forming, welding and handling can change stainless surface condition. Final treatment should match the service environment and project specification.
Industrial Finish
Suitable surface cleaning and scale removal may be specified after forming.
Pickling / Passivation
Can be specified where fabrication oxides or contamination must be removed.
Polished Surface
Food, pharmaceutical and appearance-sensitive projects may require defined finishing criteria.
Related service: Surface Finishing .
Common Stainless Steel Elliptical Head Applications
Pressure Vessels
Process vessels, receivers, reactors and pressure-containing equipment.
Storage & Process Tanks
Chemical, pharmaceutical, food, beverage and industrial storage systems.
Heat & Process Equipment
Equipment requiring formed stainless vessel ends under customer-approved design.
Stainless Steel Elliptical Head Production Examples
Stainless Steel Elliptical Head RFQ Checklist
For an accurate quote, send a drawing whenever possible. At minimum, define the following information.
- Head type: 2:1 ellipsoidal or other specified geometry.
- Governing code: ASME BPVC, EN 13445, GB or project specification.
- Material: exact grade and material specification.
- Diameter basis: ID, OD or shell-fit diameter.
- Finished thickness: minimum required thickness after forming.
- Corrosion allowance: if applicable to vessel design.
- Straight flange: required length.
- Total head height: if controlled by assembly layout.
- Edge preparation: plain / bevel plus bevel angle and root face.
- Forming route: if specifically controlled by the project.
- Heat treatment: when required by material, forming procedure or governing code.
- Surface treatment: pickled, passivated, polished or project-specific finish.
- NDE: PT, UT, RT or other examination when required.
- Documentation: MTC, traceability, inspection report and third-party inspection if required.
- Quantity: number of heads.
- Destination: delivery port, packing and Incoterm.
Related Stainless Steel Resources
Technical Reference Notes
ASME BPVC Section VIII Division 1
ASME Section VIII Division 1 covers pressure-vessel design, fabrication, inspection, testing and certification requirements.
ASTM A240/A240M
ASTM A240/A240M covers stainless plate, sheet and strip used for pressure vessels and general applications.
Stainless Steel Elliptical Head FAQ
1. What is a stainless steel elliptical head?
It is a formed stainless steel vessel end used to close pressure vessels, tanks and process equipment. A common configuration is the 2:1 ellipsoidal head.
2. What does 2:1 ellipsoidal head mean?
It refers to the geometry of the generating ellipse: the full major axis is twice the full minor axis. For ideal 2:1 geometry, the inside crown depth is approximately one-quarter of the inside diameter.
3. What is the depth of a 2:1 elliptical head?
The theoretical internal crown depth from the tangent line to the inside apex is approximately D/4, where D is the inside diameter. Straight-flange length is additional.
4. Is an elliptical head stronger than a torispherical head?
The two geometries have different pressure-design equations and stress distributions. The appropriate head should be selected using the applicable pressure-vessel code rather than a universal strength percentage.
5. Is a hemispherical head stronger than an elliptical head?
A hemispherical shape is structurally efficient under pressure, but it is deeper and can be more demanding to fabricate. Final selection depends on pressure design, vessel layout, fabrication and cost.
6. What stainless grades can be used for elliptical heads?
Common choices include 304 / 304L and 316 / 316L. Stabilized, duplex or higher-alloy grades may also be considered when material properties, forming and project requirements permit.
7. Are elliptical heads seamless?
A head may be formed from one plate blank where plate size and manufacturing capacity permit. Large or special heads may use an approved welded-blank or other fabrication route under the governing code.
8. Are elliptical heads threaded to the vessel?
Pressure-vessel heads are normally prepared for welded attachment to the shell. Edge bevel and weld preparation should match the approved joint design.
9. What inspection should be specified?
Depending on the project, inspection may include MTC review, traceability, dimensional inspection, minimum-thickness checks, PMI, PT, UT / RT and third-party inspection.
10. What information is needed for a quotation?
Send the head type, code, grade, diameter basis, finished thickness, straight flange, edge preparation, surface requirement, inspection scope, quantity and destination. A drawing is strongly preferred.
Order Elliptical Heads by Finished Geometry—not Diameter Alone
A complete elliptical-head specification should define more than “316L + 2000 mm diameter.”
The supplier needs: geometry + diameter basis + minimum finished thickness + straight flange + material specification + weld preparation + inspection + governing code.