Sunk Multi-Bolt Oval Manhole Hatch Cover | JIS F 2304 Type C for Ship Tanks

Product Specification

Sunk Multi-Bolt Oval Manhole Hatch Cover | JIS F 2304 Type C for Ship Tanks

Product Overview

The JIS F 2304 Type C sunk multi-bolt oval manhole hatch cover is a recessed ship tank access cover used where the deck, tank top, or access surface needs to remain as flat as possible after installation. Its oval opening, multi-bolt fastening arrangement, gasket sealing surface, and sunk cover layout make it suitable for water ballast tanks, oil tanks, and other marine compartments where watertight or oiltight access closure is required by the vessel design.

For this Type C configuration, the manhole ring can be supplied as a one-piece cut ring rather than several butt-welded segments. This improves continuity of the sealing land and helps maintain a smoother gasket contact surface. Material, gasket compound, bolt and nut material, coating, pressure test method, and certificate scope should be confirmed according to the tank medium, installation position, class requirement, and project drawing.

Quick Specifications

• Product type: Sunk oval manhole hatch cover → recessed access cover for ship tanks and deck / tank-top arrangements.
• Standard and type: JIS F 2304 Type C → multi-bolt sunk configuration with four nominal numbers: 4535, 5040, 6040, and 6045.
• Opening size range: 450 × 350 mm to 600 × 450 mm → used for personnel access and inspection opening selection.
• Bolt quantity: 20 to 24 bolts → multi-point compression for gasket sealing around the oval cover.
• Reference weight: 56.3 to 79.1 kg → useful for handling, packing, installation planning, and freight estimation.
• Material options: mild steel or stainless steel → final material grade should follow JIS / project drawing / class requirement.
• Gasket options: Buna A, neoprene, oil-resistant or ageing-resistant rubber → gasket selection depends on water, oil, temperature, and chemical exposure.
• Surface treatment: Sa 2.5 blasting + epoxy shop primer, galvanized, polished, or specified finish → selected according to steel material, compartment medium, and coating specification.

Main Technical Parameters

Selection & Inquiry Guide

Step 1: Confirm JIS F 2304 Type C and nominal number 4535, 5040, 6040, or 6045 according to the tank access opening, vessel drawing, and available installation space.

Step 2: Confirm application type: watertight, oiltight, or project-specific gas-tight requirement. Gas-tight use should be stated only with confirmed gasket, test pressure, and approval requirement.

Step 3: Confirm material: mild steel, stainless steel, or specified steel grade; confirm bolt and nut material such as stainless steel, bronze, brass, or project-specified material.

Step 4: Confirm gasket material, gasket thickness, medium exposure, temperature condition, and whether oil-resistant, ageing-resistant, Buna A, neoprene, or customized gasket is required.

Step 5: Confirm surface treatment: Sa 2.5 blasting with epoxy shop primer, galvanized finish, polished stainless steel, or coating system according to the tank and vessel painting specification.

Step 6: Confirm test and certificate scope before quotation: hydraulic pressure test, leak test, maker certificate, material certificate, mill certificate, class witness inspection, or other project requirement.

Step 7: Provide quantity, delivery destination, required delivery time, installation drawing, tank medium, and reference photos if replacement matching is required.

Structure

Sunk oval cover | One-piece cut manhole ring | Multi-bolt fastening | Gasket sealing surface | Seat / coaming interface | Optional stainless / bronze / brass fasteners | Recessed deck or tank-top arrangement | Shop primer or specified surface treatment

Sealing, Installation & Engineering Advantages

• Sunk Type C design keeps the cover lower than a raised arrangement, helping reduce deck or tank-top obstruction and reducing the risk of stud or cover damage during cargo handling or maintenance movement.
• The oval opening provides practical access while keeping a compact footprint around the tank structure, which is useful for ballast tanks, oil tanks, and confined shipboard spaces.
• Multi-bolt compression distributes gasket load around the oval sealing surface. Bolt tightening sequence, gasket condition, and surface flatness should be controlled during installation and after maintenance.
• A one-piece cut ring avoids butt welds across the sealing land, supporting smoother gasket contact and reducing local discontinuities that may affect watertight or oiltight sealing.
• The gasket surface should be cleaned, dressed, and protected before installation because coating build-up, weld spatter, corrosion, or handling marks can affect tightness.
• Mild steel construction with shop primer is suitable for normal shipbuilding supply; stainless steel or alternative fastener materials can be discussed where corrosion exposure or maintenance practice requires it.
• Hydraulic pressure testing or leak testing should follow the project specification and class survey requirement rather than being assumed as the same for every tank or installation position.
• Replacement orders should check the old cover dimensions, bolt pattern, gasket seat, recess depth, and marking carefully because similar oval covers may differ by standard, type, or nominal number.

Custom Attributes

• Standard: JIS F 2304 Type C → use when the vessel drawing specifies a sunk multi-bolt oval manhole arrangement.
• Nominal No.: 4535 / 5040 / 6040 / 6045 → selected by opening size and standard drawing dimensions.
• Application Type: Watertight / oiltight / gas-tight by project confirmation → sealing class depends on gasket, fastening, test pressure, and approval scope.
• Main Material: Mild steel or stainless steel → exact grade should be confirmed before production.
• Ring Workmanship: One-piece cut ring → avoids multiple butt-welded ring segments and supports a continuous sealing surface.
• Gasket Material: Buna A / neoprene / customized rubber → selected according to tank medium and service condition.
• Bolt & Nut Material: Stainless steel / bronze / brass / specified material → selected according to corrosion exposure and project requirement.
• Surface Treatment: Sa 2.5 blasting + epoxy shop primer / galvanized / polished / customized → final finish should match material and vessel coating specification.
• Test Requirement: Hydraulic pressure test or leak test according to project → pressure value and witnessing scope must be confirmed before quotation.
• Certificate Requirement: Available according to order scope → class certificate and witness inspection are subject to class approval and project requirement.

How It Works

Tank opening is prepared according to the drawing → Sunk ring / seat is installed into the deck or tank top → Gasket is placed on the sealing land → Oval cover is fitted and bolts are tightened in sequence → Tightness test and coating repair are completed according to project requirement

Applications

Water ballast tanks | Oil tanks | Ship deck access openings | Tank-top manholes | Cargo hold access areas where a flush arrangement is required | Newbuilding projects | Repair and replacement of JIS Type C manholes

Certifications & Advantages

Certificates can be arranged according to project requirement, inspection scope, material traceability, test method, and class society approval procedure.

Certification: CCS, NK, BV, ABS, DNV, LR, KR, IRS, RS, RINA, CRS, Makers Test Certificate — available upon request and subject to project confirmation.

Drawing & Photos

FAQ

Q1: What is the main difference between JIS F 2304 Type C and raised manhole cover types?

A1: Type C is a sunk or recessed multi-bolt oval cover. It is selected when the deck or tank top should remain less obstructed and when exposed studs or raised cover edges may interfere with cargo handling, maintenance movement, or working access.

Q2: Can this manhole cover be supplied as watertight, oiltight, or gas-tight?

A2: Watertight or oiltight use is normally based on the cover structure, gasket material, bolt compression, installation quality, and required test. Gas-tight use should be confirmed separately because it depends on gasket selection, test pressure, medium, and approval requirement.

Q3: What information is needed for replacement orders?

A3: Please confirm the standard and type, nominal number, opening size, bolt quantity and pitch, cover and seat dimensions, gasket material, material grade, surface treatment, tank medium, certificate requirement, and photos or drawings of the existing manhole.