Oval Raised-Coaming Marine Manhole Cover | Multi-Bolt Watertight and Oiltight

Product Specification

Oval Raised-Coaming Marine Manhole Cover | Multi-Bolt Watertight and Oiltight Access (CB/T 4392 Type AA)

Product Overview

The CB/T 4392 Type AA marine manhole cover is an oval, raised-coaming, multi-bolt access closure for steel ship structures. The raised coaming is welded to the deck, tank top, or bulkhead opening, while the removable cover is compressed against a gasket by multiple fasteners to provide a controlled watertight or oiltight seal.

Type AA is mainly relevant to replacement, compatibility, and vessel projects that still specify the legacy CB/T 4392 dimensions. CB/T 4392-2014 was withdrawn on 12 December 2023. For newbuilding projects, the applicable current reference should be confirmed against GB/T 43383-2023, which is identical to ISO 5894:2018, together with the vessel specification, approved drawing, tank service, pressure direction, and classification requirements.

Quick Specifications

• Product type: Oval raised-coaming marine manhole cover → provides bolted access through ship decks, tank tops, or bulkheads while keeping the opening above the surrounding plating.
• Legacy standard and type: CB/T 4392-2014 Type AA → suitable for replacement and compatibility where the vessel drawing specifically calls for this configuration.
• Nominal opening sizes: 450 x 350 / 500 x 400 / 600 x 400 / 600 x 450 / 800 x 600 mm → covers common personnel-access and inspection-opening sizes.
• Fastening arrangement: M20 multi-bolt closure with 18 to 26 fasteners in the supplied table → distributes gasket compression around the oval sealing perimeter.
• Plate combinations: S / S1 thickness pairs from 4 / 4 mm to 24 / 22 mm → selected according to nominal size, service, pressure, and approved construction drawing.
• Calculated weight: 17.4 to 199.7 kg from the detailed supplied table → relevant to manual handling, lifting-point planning, hinge or handle requirements, and installation sequence.
• Tightness basis: Watertight and oiltight when correctly designed, assembled, gasketed, tightened, and tested → gastight service requires separate project confirmation and an approved leakage-test procedure.
• Material and finish: Mild steel or stainless steel body with project-selected fasteners and coating → gasket seat, threads, welded interface, and corrosion compatibility require specific control.

Main Technical Parameters

Selection & Inquiry Guide

Step 1: Confirm whether the requirement is a legacy CB/T 4392 Type AA replacement or a newbuilding manhole cover to the current project standard.

Step 2: Confirm nominal opening size, installation position, deck / tank-top / bulkhead orientation, available coaming height, and opening reinforcement.

Step 3: State the compartment and medium: ballast water, freshwater, fuel oil, lubricating oil, void space, cofferdam, or other service; provide design pressure, test pressure, and pressure direction.

Step 4: Confirm S / S1 thickness combination, body material, gasket material, cover handling arrangement, and whether welded studs or threaded / replaceable bolts are required.

Step 5: Confirm fastener material, washer arrangement, corrosion compatibility, coating or galvanizing scope, gasket-seat protection, and required tightening or torque procedure.

Step 6: Confirm watertight / oiltight / separately approved gastight requirement, hydraulic or air-leak test method, class society, certificate scope, quantity, destination, and required delivery time.

Structure

Oval cover plate | Raised welded coaming | Continuous gasket seat | Replaceable sealing gasket | M20 multi-bolt arrangement | Nuts and washers | Optional handle or lifting point | Deck / tank-top / bulkhead weld interface | Specified coating system

Sealing, Fastening & Fabrication Advantages

• The raised coaming lifts the sealing joint above the surrounding plating and provides a defined welded interface for the ship structure; the coaming height and opening reinforcement should follow the approved drawing.
• The oval opening provides personnel and inspection access while limiting the transverse opening width compared with a circular access opening of similar usable length.
• Multiple fasteners distribute compression around the gasket perimeter. Bolt spacing, cover flatness, gasket-seat flatness, and a cross-tightening sequence are important to avoid local leakage.
• Welded studs can simplify repeated opening where the approved design protects the threads and welds; threaded or replaceable bolts can support maintenance replacement. The selected arrangement should not be changed without drawing approval.
• Gasket material should be selected for the contained medium, temperature, ageing, compression set, and fire-safety requirement. Watertight service does not automatically confirm oil or gas compatibility.
• For carbon-steel covers, Sa 2.5 blasting and an epoxy shop primer can be used as the production reference, while sealing faces, threads, stainless components, and final ship coating require controlled masking and touch-up.
• Where stainless-steel, bronze, or brass fasteners are combined with carbon-steel structures, galvanic compatibility, anti-seize compound, washer material, and future removal should be considered.
• Hydraulic pressure testing or air-leak testing can be arranged according to the approved procedure. Test pressure, holding time, leakage acceptance, and witness requirement must be confirmed before production.

Custom Attributes

• Standard Status: CB/T 4392-2014 withdrawn → retain for legacy replacement and dimensional compatibility; confirm GB/T 43383-2023 / ISO 5894:2018 for new projects.
• Type: AA oval raised-coaming multi-bolt configuration → fixed coaming with removable bolted cover.
• Nominal Size: 450 x 350 to 800 x 600 mm → select according to access need and available structural space.
• Tightness: Watertight / oiltight according to approved design and test → gastight performance is project-specific and not assumed.
• Fastener Arrangement: Welded studs or threaded / replaceable bolts → final arrangement follows the approved fabrication drawing.
• Fastener Material: Stainless steel / bronze / brass as specified → select for strength, corrosion, galling, and compatibility with the cover material.
• Body Material: Mild steel or stainless steel → exact grade, thickness, and welding consumables to be confirmed.
• Gasket: Material and cross-section to be confirmed → select according to medium, temperature, pressure, and class requirement.
• Surface Treatment: Sa 2.5 blasting + epoxy shop primer, polished stainless steel, galvanizing, or project coating → keep gasket seats and threads suitable for assembly.
• Certificate Requirement: Available according to project scope → material traceability, dimensional inspection, leak-test record, and class witnessing should be agreed before quotation.

How It Works

Raised coaming is welded into the ship structure → Gasket is seated on the continuous sealing surface → Oval cover is positioned → M20 fasteners are tightened progressively in a cross pattern → Uniform gasket compression forms the seal → Hydraulic or air-leak testing confirms the agreed tightness requirement

Applications

Ballast tanks | Freshwater and technical-water tanks | Fuel-oil or lubricating-oil tanks subject to gasket and project approval | Cofferdams | Void spaces | Deck and tank-top access openings | Merchant vessel repair and replacement projects

Certifications & Advantages

Material certificates, gasket documentation, dimensional inspection records, hydraulic or air-leak test reports, maker documentation, and class witnessing can be arranged according to the project specification and agreed order scope. The product should not be presented as class-approved by default; approval and certification remain subject to order, inspection, and class procedure.

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

Drawing & Photos

FAQ

Q1: Is CB/T 4392-2014 still the current marine manhole-cover standard?

A1: No. The official standard-information platform lists CB/T 4392-2014 as withdrawn on 12 December 2023. It remains useful for legacy replacement and dimensional compatibility. GB/T 43383-2023, identical to ISO 5894:2018, is the current general Chinese standard for bolted marine manhole covers.

Q2: How should the S / S1 thickness combination be selected?

A2: Do not select thickness only by opening size. Confirm installation location, pressure direction, design and test pressure, surrounding structure, corrosion allowance, material grade, service medium, and approved vessel drawing. The supplied table provides standard combinations and calculated weights for initial selection.

Q3: Can the same Type AA cover be used for water, oil, and gas service?

A3: Watertight and oiltight service depend on the approved construction, gasket, bolt preload, and test. Gastight service requires a separately specified leakage criterion, compatible gasket and fasteners, an approved test procedure, and project or class acceptance.