What this part family includes
Welded steel cylindrical shells appear in many machines: conveyor rollers, dryer drums, mixer barrels, kiln sections and pressure equipment bodies. Each one begins as plate that is rolled, welded into a tube, then machined at the ends and at bearing or sealing seats. When you send a request for quotation to a contract manufacturer, the drawing and the supporting documents decide whether the shop can price the part accurately and build it to spec.
This article walks through the inputs, tolerances, welding scope and inspection evidence that matter for cylindrical shells made to customer drawings. It is written for procurement managers, equipment designers and plant engineers who buy fabricated and machined components rather than finished machines.
Drawing and bill of materials readiness
The most useful document is the manufacturing drawing. It should show the shell diameter, wall thickness, overall length, material grade, and the location and size of every machined feature such as journals, bearing seats, flange faces and bolt circles. A bill of materials should list the plate and any bought in items, with grades and quantities.
If the drawing only shows a general arrangement, ask the design office to release a fabrication drawing before the shop quotes. A contract manufacturer can often help review the drawing, but that review is a service, not a substitute for a released design. Where the geometry is not fully defined, the quotation will carry assumptions that you must confirm later.
Wall thickness, diameter and material
State the nominal diameter and wall thickness as ranges only when the design accepts them. Cylindrical shells are sensitive to out of roundness after rolling and welding, so the drawing should define both the diameter tolerance and the allowable deviation from a true circle. Material grade drives welding consumables and heat treatment, so name the standard and grade rather than a generic description.
Consider how the shell is handled and shipped. A long thin shell distorts more easily than a short stiff one, and that affects both the welding sequence and the machining datum. These details belong in the RFQ so the quotation covers the right operations.
Welding scope and code
Most cylindrical shells are welded longitudinally and, where ends or stiffeners are added, circumferentially. The welding specification should state the code, filler metal, joint preparation and any post weld heat treatment. Common references are AWS D1.1 for structural steel welding and ISO 3834 for the quality requirements of fusion welding of metallic materials. Weld quality grades such as those in ISO 5817 help the shop and the buyer agree on what an acceptable weld surface looks like.
State who supplies the welding procedure specification and the procedure qualification record. On some projects the buyer provides them; on others the manufacturer develops and qualifies them. This division of responsibility should be written into the purchase order, because it affects both price and lead time.
Machined features and tolerances
The machined work is where cylindrical shells earn their function. Bearing seats, shaft journals and sealing faces need controlled diameters and surface finish. ISO 286 defines limits and fits for linear sizes and is a practical reference for shaft and bore seats. Where the drawing does not call out a general tolerance, ISO 2768 gives default values, and geometric controls such as runout and cylindricity are usually handled under ASME Y14.5 or ISO 1101.
Tell the manufacturer the fit you need rather than only a diameter. A seat that must carry a bearing needs a different tolerance than a clearance used only for alignment. Over tightening every dimension raises cost without improving the part.
Balance and rotating behaviour
Shells that rotate at speed need dynamic balance. ISO 1940-1 sets balance quality grades for rigid rotating bodies and is the usual reference when a drawing calls for balancing. The required grade depends on the service speed and the consequence of vibration, so state the maximum operating speed and the acceptable residual unbalance.
Where the shell is long or thin, welding distortion can move the centreline before machining. A sensible sequence machines reference diameters after final welding, then checks runout against the machined datum. Discuss this sequence in the RFQ so the quotation covers the right operations.
Material certificates and traceability
Specify the material certificate you require. EN 10204 describes inspection documents, and a 3.1 certificate is common for welded and machined parts where traceability matters. The certificate should identify the heat or batch and the tested properties. Keep this requirement in the RFQ, because adding it after production usually means re testing or extra paperwork.
Inspection, finishing and handover
Agree on the dimensional and visual checks before the order is placed. For first articles, a measured report against the drawing, including diameters, lengths and runout, gives both sides a record to work from. Surface treatment, coating and protective packaging for export are also scope decisions: state whether the manufacturer applies them or whether they are handled downstream.
Typical production flow
A typical sequence rolls the plate, welds the longitudinal seam, stress relieves or straightens as needed, then machines the ends and seats, balances if required, inspects and packages. The order of welding and machining matters because each step can shift the geometry. Define the acceptance steps you want signed off, and the quotation will reflect that scope.
Where to look next
If your enquiry covers structural welding, the note on welding procedure and NDT requirements explains what to include in the welding section of an RFQ. For the wider scope, the contract manufacturing services page lists the part types and processes supported.