The manhole cover ring is the welded-in or bolted interface on the top of a tank or silo semi-trailer that carries the inspection hatch, fill opening and safety vent hardware. It must seal under internal pressure, vibration and thermal cycling while resisting product corrosion. Ningbo Ruican supplies these rings investment cast in stainless or carbon steel with machined sealing faces and true bolt circles, solving the chronic problems of ovalised rings, misaligned hinge lugs and gasket creep that cause leaks in bulk and food-grade haulage.
Specifications
| Item | Detail |
|---|---|
| Casting process | Silica sol investment casting (water glass option for large diameter rings) |
| Material options | Stainless steel 304 / 304L / 316 / 316L; carbon steel 1020, 1045; ductile iron EN-GJS-450-10 |
| Dimensional tolerance (ISO 8062-3 CT grade) | CT6–CT7 as cast, CT5 on machined sealing face and bolt circle |
| Machining | Vertical turning and 4-axis machining: sealing face, bolt circle drilling and tapping, hinge lug milling, weld-prep bevel |
| Surface finish (Ra) | Ra 6.3 µm as cast; Ra 1.6–3.2 µm machined; Ra 0.8 µm polish and electropolish for food-grade |
| Weight range | 3.0 kg – 22.0 kg |
| Typical lead time | Tooling 5–7 weeks; samples 6–8 weeks; production 5–7 weeks |
Scope and options
Key features
- Near-net-shape ring casting minimises weld length on the tank shell, reducing distortion during shell welding.
- Machined flat sealing face with controlled Ra holds gasket compression evenly around the full circumference.
- Moreover, Integral hinge lugs, clamp seats and earthing bosses cast in, eliminating separate welded brackets.
- Generally, Accurate bolt circle and true roundness remove the fit-up rework common with rolled or flame-cut rings.
- 316L and electropolished finishes available for food-grade, milk, beverage and chemical tank service.
- Full penetration weld-prep bevel machined to your welding procedure specification for repeatable shell welding.
Applications
- Bulk powder and pneumatic dry-bulk silo semi-trailers
- Food-grade milk, juice and edible-oil tank trailers
- Chemical and corrosive liquid tank containers
- Fuel and petroleum product road tankers
- Bitumen and asphalt insulated tank trailers
- Static storage tanks and mobile processing vessels
Quality & compliance
Ningbo Ruican produces manhole cover rings under an IATF 16949 certified system, with APQP documentation and PPAP submission at level 3 or 4 for OEM tank builders. Material certification with heat-lot traceability and EN 10204 3.1 documentation is standard, and positive material identification can be added for stainless grades. Moreover, dimensional reports cover roundness, sealing face flatness and bolt circle position from CMM inspection. Weld procedure support, dye penetrant testing of the weld prep, hydrostatic and pressure testing, and salt-spray validation to ASTM B117 are available on request.
FAQ
Can you supply 316L rings for food-grade tank trailers?
Yes. We cast 316L routinely and can deliver machined plus electropolished surfaces down to Ra 0.8 µm. We control carbon content, supply mill certification with heat-lot traceability, and can add ferrite checks and positive material identification where your hygiene specification or customer audit requires it.
Do you machine the weld-prep bevel?
We do. The bevel geometry is machined to your welding procedure specification so your shell fit-up and weld penetration are consistent from the first tank to the thousandth. Consistent bevels also reduce weld metal consumption and the post-weld grinding that follows an inconsistent flame-cut ring.
How flat is the sealing face you can hold?
We typically hold sealing face flatness within 0.10 mm across the ring, tighter where the gasket specification demands it, and verify by CMM or dial indicator per your control plan. Achievable flatness depends on ring diameter and section, so send the drawing and we will confirm during feasibility review.
Can you cast our existing ring design with lugs and bosses?
Yes, that is exactly the value of investment casting. Hinge lugs, clamp seats, earthing bosses and nameplate pads are cast integrally, which removes bracket welds and the fit-up and inspection time they carry. Send the model and we will review draft, section thickness and machinability before tooling.
What testing do you offer to prove the ring seals?
We can arrange hydrostatic or pneumatic pressure testing of the assembled hatch, dye penetrant inspection of the weld prep and finished machined surfaces, and salt-spray testing to ASTM B117. Generally, test plans and results are documented and included in the PPAP submission package for your approval.
CTA
Send your manhole cover ring drawing, material grade, diameter and annual volume to Wendy She at sales@cnsandcasting.com, or reach Wendy She on WhatsApp at +86-13777124360. You will receive a feasibility review, casting and machining proposal, and budgetary tooling and piece pricing from Ningbo Ruican, so you can move your tank programme forward with confidence.
