Screw caps - Pipe thread G 1 to G 6
1Key Takeaways
This standard applies to screw caps for covering, for example, filling and direction finding tubes and other pipe ends on ships.
2Expert Interpretation
An in-depth interpretation of the German DIN 86121:2018 marine screw cap standard, covering key technical parameters such as dimensional specifications, material requirements, and vent hole design for G1 to G6 threaded caps, suitable for sealing and protection applications in ship piping systems.
Standard Overview and Technical Background
DIN 86121:2018 is the technical standard for marine screw caps published by the German Institute for Standardization, replacing the 1984 version. This standard specifically regulates screw caps for G1 to G6 pipe threads. It is primarily used for end sealing protection in marine piping systems, particularly in critical areas such as filling and measuring pipes.
Analysis of main technical parameters
| Nominal size | Thread specification | Outer diameter d2(mm) | Height h(mm) | Mass (kg) |
|---|---|---|---|---|
| 1 | G1 | ⌀42 | 21 | 0.20 |
| 1¼ | G1¼ | ⌀52 | 21 | 0.28 |
| 1½ | G1½ | ⌀58 | 22 | 0.34 |
| 2 | G2 | ⌀70 | 22 | 0.43 |
| 2½ | G2½ | ⌀90 | 23 | 0.71 |
| 3 | G3 | ⌀105 | 23 | 0.97 |
Structural Design and Functional Characteristics
The standard defines the complete structural configuration of Type A screw cap, including:
- Main body cap: Made of copper-tin alloy (CuSn10-C) or copper-zinc alloy (CuZn37Pb2Ni1AlFe-C)
- Flat washer: Resistant to seawater and fuel oil, with a temperature resistance of up to 80°C
- Safety chain: Utilizes a 2.5mm node chain in accordance with DIN 5686
- S-hook: Made of stainless steel X5CrNi18-10 for corrosion resistance
The key vent design is a significant improvement over the 2018 standard. The 5mm diameter side vent effectively eliminates pressure buildup in the pipes while preventing seawater from entering the piping system when closed.
Comparative Analysis of Material Specifications
| Part Number | Part Name | Material Brand | Material Standard | Technical Characteristics |
|---|---|---|---|---|
| 1 | Cap | CuSn10-C/CuZn37Pb2Ni1AlFe-C | DIN EN 1982 | Seawater Corrosion Resistance |
| 2 | Gasket | Elastomeric Sealing Material | ISO 7619-1 | Shore A Hardness 75±5 |
Standard Evolution and Technical Updates
Compared with the 1984 version, DIN 86121:2018 has four major updates:
- Material Identification Update: Adopting a modern material naming system to align with international standards
- Normative Reference Update: Citation of the latest DIN EN ISO and DIN 5686 standards ISO standard
- Graphic revisions: Optimize technical drawings to improve readability and accuracy
- Structural adjustments: Follow current standard compilation rules to improve ease of use
The historical evolution of the standard can be traced back to the HNA Sr 12 standard in 1921. It has undergone multiple revisions in 1972 and 1984, reflecting the continuous development of German ship engineering technical standards.
Application Scenarios and Implementation Recommendations
DIN 86121:2018 screw caps are mainly used in the following scenarios:
- Ship fuel tank systems: End sealing of filling and measuring tubes
- Temporary pipeline closures: Pipeline protection during construction and maintenance
- Pressure balancing systems: Used in conjunction with DIN 86110 standards
Implementation Recommendations: When selecting screw caps, the thread specifications should be accurately matched according to the nominal size of the pipe, ensuring the compatibility of the gasket material with the medium. The integrity of the safety chain should be checked regularly to prevent the cap from falling off in severe sea conditions.
Key points of quality control and inspection
The standard requires manufacturers to ensure the following quality control points:
- Thread dimensions comply with DIN EN ISO 228-1
- Washer hardness is controlled within Shore A 75±5
- Material certificates comply with relevant DIN EN standards
- Ventilation hole position and size precisely meet drawing requirements
Through strict quality control, the long-term and reliable operation of the screw cap in the harsh environment of ships is ensured.