When selecting valves for shipbuilding and marine applications, it is important to first establish the operating conditions that do not exist in land-based equipment: salt damage, vibration, inclination, and limited maintenance opportunities. There are three broad axes for selection. First is corrosion resistance (material and surface treatment); second is a structure that withstands vibration and shock along with seat reliability; and third is conformity to the applicable classification society rules and standards. Because the required performance differs by application (seawater systems, fresh water systems, fuel oil systems, steam systems, and air systems), the basic approach is to start from the three conditions of fluid, temperature, and pressure, then narrow down the choice by overlaying environmental load and maintainability. The following sections organize the criteria for making these decisions in order.
Key points of this article
- For marine use, “salt damage, vibration, inclination, and maintenance constraints” become the prerequisites for selection
- Narrow down along the three axes of material, structure, and standard conformity, then apply the conditions by application
- Material selection and standard conformity are where confusion most often arises. Early technical consultation prevents rework
Conditions required of marine valves in harsh environments
The environment to which marine valves are exposed differs in its premises from land-based plant piping. Understanding the representative load conditions in advance helps keep material and structure selection from wavering.
Resistance to salt damage and corrosion
At sea, valves are constantly exposed to salt-laden air, and in seawater piping systems the internal surfaces are also placed in a corrosive environment. In general, for direct seawater systems, materials with high seawater corrosion resistance such as aluminum bronze or certain stainless steel grades are candidates, and the external surfaces are protected with coatings or surface treatment. For systems with milder fluid conditions, such as fresh water systems and air systems, standard materials such as bronze or gray cast iron may be sufficient. The starting point is to differentiate the material by “which system and what kind of fluid.”
Strength against vibration, shock, and inclination
Because vibration and shock from the main engine, auxiliary machinery, and wave action are applied continuously, loosening of threads, wear of seat faces, and deterioration of seals tend to progress faster than on land. In addition, reliable opening, closing, and shut-off are required even under rolling and inclination. It is reassuring to confirm the support rigidity of the handle and stem, the reliability of the seat structure, and provisions against loosening, together with the static pressure and temperature performance.
Conformity to classification society rules and standards
For marine equipment, approval by a classification society or conformity to related standards may be required depending on the application and the compartment in which the equipment is installed. Since the conformity requirements vary by ship type, compartment, and fluid, determining “which approvals and standards this system requires” at the early stage of selection makes it easier to avoid replacements and rework in later processes.
How to narrow down the selection starting from the application
Once the conditions are established, the actual selection is easier to organize when it proceeds starting from the application.
Fix the three conditions of fluid, temperature, and pressure first
First, clarify the fluid type of the target system (seawater, fresh water, fuel oil, lubricating oil, steam, compressed air, and so on), the operating temperature, and the operating pressure. These three conditions serve as the primary screening for the material, seat material, and valve type. For example, in steam systems, heat resistance and seat material are high-priority decision axes, while in seawater systems, corrosion resistance is the key axis.
Factor in maintainability and space
At sea, opportunities for parts procurement and large-scale overhaul are limited. Ease of disassembly and inspection, availability of consumable parts, installation space, and piping interfaces are elements to value on a par with performance. In confined areas, confirming even the operating direction and handle position helps reduce the maintenance burden after the vessel enters service.
Make a final check of the bore size and connection specifications
Once the valve type and material are decided, compare the bore size, connection method (flanged, threaded, etc.), and face-to-face dimensions against the piping specifications. Especially when selecting an equivalent to an existing product, confirming that the dimensions and connection standards match is essential. Because a mistake here directly leads to rework at the installation stage, we recommend verifying against drawings.
Frequently asked questions
Q1. Should the material be differentiated between seawater systems and fresh water systems?
A1. In general, it is basic to consider them separately. Select according to the fluid conditions: highly corrosion-resistant materials for direct seawater systems, and standard materials for systems with low corrosion load.
Q2. What is the difference between marine valves and land-use valves?
A2. The main differences are the consideration of salt damage, vibration, and inclination, and whether classification society and standard conformity is required. Even though the basic principles are the same, the prerequisites for selection differ.
Q3. Is classification society approval always required?
A3. It depends on the application, compartment, and fluid. Since there are systems for which approval is required and systems for which it is not, we recommend confirming the requirements at the early stage of selection.
Q4. What should be checked as a measure against vibration?
A4. The reliability of the seat structure, the support of the stem and handle, and provisions against loosening are useful guides. Confirming these together with the static performance is reassuring.
Q5. How should an equivalent to an existing valve be selected?
A5. In addition to fluid, temperature, and pressure, cross-check the bore size, connection method, and face-to-face dimensions against the drawings. If the specifications are unknown, please consult us based on information from the actual product.
Q6. What is the minimum information that should be prepared for selection?
A6. The fluid type of the system, operating temperature, operating pressure, bore size, and connection specifications are the basics. With these, a primary narrowing-down is possible.
Summary
The basic approach to selecting marine valves is to establish the prerequisites of salt damage, vibration, inclination, and maintenance constraints, then narrow down along the three axes of corrosion resistance (material), structural reliability, and standard conformity, starting from the application. By fixing the three conditions of fluid, temperature, and pressure first, and factoring in maintainability and connection specifications, you can more easily reduce rework and trouble after the vessel enters service.
If you find yourself uncertain at a stage such as “I cannot judge which material is suitable for a seawater system,” “I understand the operating conditions but cannot identify the applicable classification society rules or standards,” or “I want to select an equivalent to an existing valve based on its dimensions,” you are welcome to consult us from the stage of organizing the conditions. Whatever you can share about the fluid, temperature, pressure, bore size, and connection specifications of the system is fine, so please feel free to contact Yoshitake for technical and selection consultation. We will propose a selection suited to your application.