GB 11628 Type C Flush Multi-Bolt Marine Manhole Cover | 450 & 600 mm Cleanout Access

GB 11628 Type C Flush Multi-Bolt Marine Manhole Cover | 450 & 600 mm Cleanout Access

Product Overview

The GB 11628 Type C flush multi-bolt marine manhole cover is a round, low-profile bolted access closure for watertight or oiltight openings in steel ship structures. It may be arranged on tank tops, decks, bulkheads, hatch-cover panels, void-space boundaries, or designated cleanout openings where the approved vessel drawing calls for a removable cover rather than a hinged access hatch.

The assembly consists of a cover plate, welded mounting or seat ring, continuous gasket, studs or bolts, washers, and nuts. Multiple M20 fasteners distribute gasket compression around the circular sealing face. Correct selection requires confirmation of the legacy Type C dimensions, installation boundary, design liquid head or pressure, plate thickness, gasket compatibility, fastener material, surrounding reinforcement, and required inspection scope.

Quick Specifications

• Product type: Type C round flush multi-bolt manhole cover → provides removable cleanout or inspection access with a low-profile deck or bulkhead arrangement.
• Legacy standard: GB 11628-1989 → suitable for replacement, repair, or project drawings that specifically identify the former Chinese Type C designation.
• Current standard reference: GB/T 43383-2023 / ISO 5894:2018 → should be checked for new projects; dimensional interchangeability with the legacy Type C design is not assumed.
• Nominal opening sizes: 450 mm and 600 mm → select according to access purpose, personnel or cleaning-tool clearance, and vessel arrangement.
• Mounting-ring outside diameter D1: 620 mm or 770 mm → determines required structural space, weld perimeter, and nearby stiffener clearance.
• Cover plate thickness s: 4-12 mm for D450 and 6-14 mm for D600 → final thickness follows the standard designation and approved boundary loading.
• Fastening arrangement: M20 with 20 bolts for D450 or 26 bolts for D600 → provides distributed gasket compression and requires controlled tightening.
• Reference mass: 32.03-79.192 kg → useful for handling and freight planning; actual mass depends on material, hardware, and final drawing.

Main Technical Parameters

Selection & Inquiry Guide

Step 1: Confirm whether the order is a GB 11628-1989 Type C replacement item or a new project requiring GB/T 43383-2023, ISO 5894:2018, a shipyard standard, or a classification-approved drawing.

Step 2: Confirm nominal opening D450 or D600, cover thickness, mounting-ring diameter, available installation envelope, and whether the cover must be flush, recessed, surface mounted, or only low profile.

Step 3: Provide the exact installation position: tank top, upper deck, bulkhead, main hatch-cover panel, void space, cargo-space cleanout opening, or other boundary. State the service liquid and the design liquid head or pressure where applicable.

Step 4: Confirm cover, seat-ring, stud/bolt, nut, washer, and gasket materials. For stainless hardware on carbon steel, confirm the required isolation and corrosion-control method.

Step 5: Confirm surface preparation, coating or polishing requirement, gasket compatibility, bolt-tightening procedure, leak-test method, material traceability, and class-survey scope.

Step 6: Provide quantity, vessel type, installation drawing, existing-cover photos and dimensions for replacement work, delivery destination, and required delivery time.

Structure

Round cover plate | Welded mounting or seat ring | Continuous sealing gasket | M20 studs or bolts | Nuts and washers | Optional lifting or handling feature according to drawing | Primer, galvanizing, polishing, or project coating

Sealing, Fastening & Installation Advantages

• The circular multi-bolt arrangement distributes clamping force around the gasket and reduces dependence on one or two local securing points.
• A flush or low-profile arrangement minimizes interference with cargo handling, cleaning, walking routes, or equipment above the opening; the actual projection of nuts and studs must be checked on the drawing.
• The removable cover provides full access to the nominal opening for tank cleaning, inspection, debris removal, or maintenance without adding hinge clearance.
• The sealing face, gasket groove or landing area, and mounting-ring flatness are controlled to support continuous gasket contact after welding and final tightening.
• The welded ring transfers boundary pressure and local handling loads into the surrounding deck, tank top, bulkhead, or hatch-cover structure; nearby reinforcement remains the vessel designer's responsibility.
• Individual fasteners can be inspected and replaced during service. A cross-pattern tightening sequence helps develop more uniform gasket compression and should follow the approved procedure.
• Material combinations can be selected for seawater, freshwater, oil, cargo residue, or weather exposure, subject to verified gasket compatibility and corrosion-control requirements.

Custom Attributes

• Standard: GB 11628-1989 Type C → legacy dimensional basis for specified replacement or repair projects.
• Current Reference: GB/T 43383-2023 / ISO 5894:2018 → use for new-project standard review; do not assume direct dimensional interchangeability.
• Opening Size: D450 / D600 mm → select by access duty and approved vessel arrangement.
• Mounting Ring Diameter: D1 620 / 770 mm → confirm surrounding plate area, welding access, and stiffener clearance.
• Cover Plate Thickness: 4-14 mm across the supplied range → select only from the applicable size row and approved drawing.
• Fasteners: M20, 20 or 26 pieces → material grade, thread form, stud length, washer type, and tightening requirement to be confirmed.
• Cover and Ring Material: Mild steel or stainless steel → exact grade and welding procedure according to project requirement.
• Gasket: Buna-N, neoprene, or project-specified material → selection depends on oil, seawater, freshwater, cargo residue, temperature, and cleaning chemicals.
• Surface Treatment: Sa 2½ blast cleaning + epoxy shop primer, galvanizing, polishing, or project system → compatibility with the installation weld and final vessel coating must be confirmed.
• Tightness and Certificate Scope: According to approved ITP and project requirement → available upon request and subject to class approval or survey involvement.

How It Works

Cover is positioned over the welded seat ring → Gasket contacts the continuous sealing face → M20 fasteners are tightened in a cross pattern → Distributed compression closes the water or oil leakage path → Fasteners are removed when cleanout or inspection access is required

Applications

Tank-top access | Upper-deck inspection opening | Steel bulkhead manhole | Hatch-cover cleanout opening | Grain or dry-cargo cleaning access | Void-space inspection | Ballast or service tank access subject to approved pressure | General cargo vessels | Bulk carriers | Tankers | Workboats | Repair and replacement projects

Certifications & Advantages

Material certificates, dimensional inspection, welding records, coating records, tightness-test documentation, and classification inspection can be arranged according to project requirement, approved drawing, and agreed survey scope.

Certification: CCS, NK, BV, ABS, DNV, LR, KR, IRS, RS, RINA, CRS, Makers Test Certificate.

Drawing & Photos

FAQ

Q1: Is GB 11628-1989 still the current standard for new marine manhole covers?

A1: No. It is a legacy standard and remains relevant when an existing vessel, repair drawing, or replacement order specifically calls for GB 11628 Type C. New projects should confirm the current standard or approved shipyard drawing before production.

Q2: Does “flush” mean that no bolts or nuts project above the surrounding plate?

A2: Not automatically. Type C is a low-profile or flush-mounted bolted arrangement, but the final projection depends on the seat-ring detail, cover recess, stud length, nut arrangement, and installation drawing. The required finished level should be stated in the inquiry.

Q3: Can this cover be used on any tank or pressure boundary?

A3: It is intended for shipboard watertight or oiltight manhole applications, not for boilers or pressure vessels. Tank service, liquid head, test pressure, material, gasket, plate thickness, surrounding structure, and class approval must be confirmed for the actual installation.