Square Semi-Flush Marine Manhole Cover | CB/T 4392 Type BC Multi-Bolt Design

Product Overview

The CB/T 4392 Type BC square marine manhole cover is a multi-bolt access closure for flat steel-ship structures such as tank tops, decks, and bulkheads. The supplied configuration uses a nominal 600 × 600 mm square opening, a semi-flush / semi-raised surrounding plate arrangement, 28 M20 fasteners, and a compressible gasket to provide watertight or oiltight sealing when the cover, seating face, gasket, fasteners, installation, and test procedure are correctly specified.

CB/T 4392-2014 is now a legacy standard: it was withdrawn on 12 December 2023. For new projects, the purchaser should confirm whether the contract requires the legacy Type BC dimensions or the current GB/T 43383-2023, effective from 1 March 2024 and identical to ISO 5894:2018. This page therefore supports replacement, repair, and project-specific supply to the stated Type BC data; final drawing, material, gasket medium compatibility, test pressure, and class scope remain subject to order confirmation.

Quick Specifications

• Product type: Square multi-bolt marine manhole cover → provides personnel access and a bolted sealing interface for designated flat areas of steel vessels.
• Standard and type: CB/T 4392-2014 Type BC → legacy Chinese marine manhole-cover configuration for projects that continue to specify this type or require replacement compatibility.
• Current-standard check: GB/T 43383-2023 / ISO 5894:2018 → confirm applicability for newbuilding projects before freezing dimensions and approval documents.
• Nominal size: 600 × 600 mm → the surrounding opening, frame, and cover dimensions should be checked against the vessel structure and supplied drawing.
• Fastening arrangement: 28 × M20 fasteners → distributed tightening is intended to compress the gasket around the square perimeter; tightening sequence and torque are project-dependent.
• Standard S range and weight: S = 10–24 mm; 67.1–124.5 kg → affects cover configuration, handling, hinge selection, and shipment weight; the exact meaning of S should be confirmed from the official Type BC drawing.
• Sealing service: Watertight and oiltight duty basis → gasket compound must match the stored medium and temperature; gastight duty is not automatic and requires separate confirmation and testing.
• Material and finish options: Mild steel or specified stainless steel, with Sa 2½ blasting plus epoxy shop primer, polishing, galvanizing, or project coating → final material grades and coating compatibility should be stated in the inquiry.

Main Technical Parameters

Selection & Inquiry Guide

Step 1: Confirm the required standard basis: legacy CB/T 4392-2014 Type BC for replacement / specified projects, or the current GB/T 43383-2023 / ISO 5894:2018 basis for a new project.

Step 2: Confirm nominal size 600 × 600, the required S value, all interface dimensions, installation location, surrounding structural thickness, and whether “semi-flush” or “semi-raised” matches the approved drawing.

Step 3: Confirm cover and surrounding-plate material grade, gasket material and service medium, fastener material / grade, welded-stud or threaded-stud arrangement, and optional hinge configuration.

Step 4: Confirm sealing duty: watertight or oiltight; for any gastight requirement, provide design pressure, leakage criterion, gasket specification, and approval requirement separately.

Step 5: Confirm surface preparation and coating system, including shop primer compatibility, stainless-steel polishing, galvanizing feasibility, final paint specification, and any insulation or dissimilar-metal control.

Step 6: Confirm test pressure, holding time, acceptance criteria, witness requirement, material traceability, maker certificate / class certificate scope, quantity, delivery destination, and required delivery time. Provide the vessel or installation drawing when available.

Structure

Square cover plate | Semi-flush / semi-raised surrounding plate | Continuous gasket seating face | Replaceable rubber gasket | 28 × M20 fasteners | Optional hinge support | Welded or threaded stud arrangement as confirmed | Steel or specified stainless-steel construction

Sealing, Installation & Quality Advantages

• The 28-fastener perimeter arrangement distributes gasket compression around the square cover, helping control local gaps when the seating faces are flat and the fasteners are tightened in a balanced cross-sequence.
• The semi-flush / semi-raised arrangement can reduce deck or bulkhead projection compared with a fully raised coaming, but the exact installation depth and structural cut-out must follow the approved drawing.
• Sealing performance depends on the complete interface—not only the gasket material. Cover flatness, seating-face finish, gasket cross-section, bolt condition, tightening procedure, coating build-up, and installation distortion should be controlled.
• Neoprene and NBR / Buna-N are common project options, but the gasket compound should be selected for the actual oil, water, temperature, weather exposure, and ageing requirements. A customized compound should be qualified before use.
• Welded studs can provide a fixed fastening arrangement, while threaded or replaceable studs may improve maintenance access. The selected method, thread engagement, corrosion protection, and replacement procedure should be confirmed before production.
• Stainless-steel fasteners or full stainless-steel construction can improve corrosion resistance in suitable environments. Material pairing, galling prevention, welding procedure, pickling / passivation, and galvanic compatibility require project-specific confirmation.
• Hydraulic pressure testing can be arranged according to the order. Test pressure, holding time, leakage acceptance, calibrated instruments, test medium, drainage, and class witness scope must be agreed before testing.

Custom Attributes

• Standard Status: CB/T 4392-2014 legacy reference → withdrawn on 12 December 2023; use only when required by contract, replacement compatibility, or approved project documentation.
• Current Reference: GB/T 43383-2023 / ISO 5894:2018 → confirm for new projects and do not assume Type BC dimensions are directly interchangeable.
• Type: BC square multi-bolt configuration → intended for a square manhole opening with the supplied semi-flush / semi-raised arrangement.
• Nominal Size: 600 × 600 mm → verify the structural opening and all L1 / B1, L2 / B2, and L3 / B3 interfaces before fabrication.
• S Range: 10 / 12 / 14 / 16 / 18 / 20 / 22 / 24 mm → select according to the official drawing or approved project specification; definition to be confirmed.
• Fasteners: M20 × 28 → material, mechanical grade, stud fixing method, nuts, washers, anti-seize, and tightening requirement should be stated.
• Gasket: Neoprene, NBR / Buna-N, or specified compound → select by medium, temperature, compression, ageing, and approval requirements.
• Material: Mild steel or specified stainless steel → exact plate grade, stainless grade, welding consumables, and material certificates are subject to order scope.
• Test: Hydraulic pressure test according to approved procedure → pressure, duration, leakage criterion, and witness requirement to be confirmed.
• Classification: Available according to project requirement → certificate type and survey scope are subject to class approval and quotation.

How It Works

Access opening is aligned with the vessel structure → Gasket is seated on a clean, flat contact face → Cover is positioned and the 28 M20 fasteners are tightened in a balanced sequence → Gasket compression forms the specified watertight or oiltight seal → The assembly is inspected and pressure-tested according to the approved procedure → Fasteners are released for maintenance access when the space is confirmed safe

Applications

Steel vessel tank tops | Flat deck access positions | Bulkhead access openings | Water tanks | Oil tanks | Void spaces | Service compartments | Newbuilding projects subject to current-standard confirmation | Legacy replacement and repair projects

Certifications & Advantages

Material certificates, maker inspection documents, hydraulic test records, and classification-society inspection can be arranged according to project requirement, order scope, material traceability, and class approval procedure. They are not assumed to be included unless stated in the quotation and purchase order.

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 standard for marine manhole covers?

A1: No. CB/T 4392-2014 was withdrawn on 12 December 2023. GB/T 43383-2023 became effective on 1 March 2024 and is identical to ISO 5894:2018. Type BC can still be quoted for legacy replacement or when the approved project documents specifically require it, but new projects should confirm the governing standard before ordering.

Q2: Does a watertight and oiltight cover automatically qualify as gastight?

A2: No. Gastight performance requires separate confirmation of design pressure, gasket material and cross-section, flange flatness, fastener loading, leakage criterion, test method, and approval scope. It should not be assumed from watertight or oiltight wording alone.

Q3: What information is required for an accurate quotation?

A3: Provide the governing standard, Type BC drawing, nominal size, S value, material grades, gasket medium and temperature, bolt material / grade and fixing method, hinge requirement, installation position, coating system, test pressure and holding time, certificate scope, quantity, destination, and delivery schedule.