Essential Guide to Industrial Valve Selection

Overview

Valves are crucial components in industrial pipelines. They have many attributes that need careful consideration. These attributes include:

1. Valve Type: The kind of valve, such as gate, globe, ball, or butterfly.
2. Basic Parameters:
   • Application Standards: Standards the valve must meet.
   • Nominal Diameter: The size of the valve.
   • Nominal Pressure Rating: The pressure the valve can handle.
   • Main Materials: Materials used to make the valve.
3. Structural Parameters:
   • Body Structure: The shape and design of the valve body.
   • Internal Type: The design of the internal parts.
   • End Connection Type: How the valve connects to the pipeline.
   • Bonnet Type: The cover on the valve body.
   • Stem Support Type: How the valve stem is supported.
   • Operation Method: How the valve is operated (manually or automatically).
4. Main Component Materials:
   • Seat Sealing Surface Material: Material of the sealing surface.
   • Disc Sealing Surface Material: Material of the disc sealing surface.
   • Stem Material: Material of the valve stem.
   • Bonnet/Body Bolt and Gasket Material: Materials used for bolts and gaskets.
5. Special Requirements:
   • Inspection and Testing Requirements: Tests the valve must pass.
   • Special Structural Requirements: Any unique structural needs.
   • Special Manufacturing Requirements: Specific manufacturing needs.

Comprehensive Considerations

For valves used in harsh environments, defining the basic attributes may not be enough. You also need to control factors affecting valve quality. These factors include:

• Manufacturing Requirements: Material smelting, forming methods, heat treatment.
• Inspection and Testing Requirements: Non-destructive inspection, strength test, sealing test, corrosion test.
• Packaging Markings and Document Publication: Proper labeling and documentation.

Engineers usually compile an order specification to explain these requirements. Process engineers or a team of process and piping engineers determine the valve type based on operational needs.

Focus on Shut-off Valves

This guide primarily introduces shut-off valves and provides selection principles. Choosing the right valve body materials is complex and often considered alongside other pipeline components. Manufacturing and inspection requirements for valves are typically specified in project procurement technical specifications.

Selection Principles

Generally, valve selection refers to similar processes or draws from the experience of similar devices. For new process technologies, especially critical valves, the selection is specified in the process package or basic design by patent licensors. Modern petrochemicals continuously introduce new products and processes.

Valves are critical components in petrochemical devices, and the successful operation of any process depends on the correct choice of valve. Therefore, selecting the right valve involves considering fluid properties, operating conditions, flow conditions, external environment, economic factors, and relevant regulations, codes, and standards.

Fluid Properties, Operating Conditions, and Flow Conditions

Fluid Properties

Fluid properties are fundamental data for chemical design, fluid mechanics calculations, thermal processes, and phase change calculations. They serve as the basis for chemical safety design, process hazard analysis (PHA), and environmental evaluation.

Key Fluid Properties

1. Chemical Properties:
   • Chemical composition, molecular formula, impurity names, and content can be retrieved from relevant literature, manuals, and databases.
2. Hazard Properties:
   • Toxicity: Acute toxicity LC50, LP50, maximum allowable concentration, carcinogenicity.
   • Flammability: Fire hazard rating, explosive limits, flash point, ignition temperature, maximum experimental safe gap (MESG), minimum ignition current ratio (MICR), ignition temperature of combustible dust.
   • Corrosiveness: Uniform corrosion, localized corrosion, intergranular corrosion, stress corrosion, erosion.
3. Physical Properties:
   • Density, viscosity, rheology, compressibility, thermal expansion coefficient, specific heat ratio, thermal conductivity, surface tension, sound velocity.
   • Phase equilibrium conditions: bubble point (boiling point), dew point (condensation temperature), melting point (freezing point), crystallization temperature, vapor pressure, solubility, critical temperature, critical pressure.
   • Conductivity, permeability to fluoroplastics.

Operating Conditions and Flow Conditions

1. Operating Conditions:
   • Besides the design conditions for normal operation, consider maximum and minimum values under all operating conditions (including startup, shutdown, testing, purging, washing, catalyst heating, reduction, accident handling, maintenance).

Important Operating Conditions

• Pressure and Temperature: Must account for all possible scenarios, including rapid changes that can cause thermal shock.
• Flow Rate: Variations can impact valve performance, causing issues like jamming or cracking.

2. Flow Conditions:
   • Flow State: Turbulent flow, laminar flow, choking flow.
   • Two-Phase Flow: Gas/Steam-Liquid (flashing, cavitation, slug flow), Solid-Gas (pneumatic transport), Solid-Liquid (suspension).
   • Unstable Flow: Water hammer.

Normal valve operation typically involves turbulent flow. High-flow-speed control or throttling valves can cause vibration or noise. Safety valves and vent valves may reach choking flow conditions when discharging. High-speed gas/steam flow containing droplets or solid particles can cause erosion.

Example of Operating Conditions and Their Effects

Comprehensive Engineering Approach

Selecting the right valve involves collaboration among various engineering disciplines. This ensures the valve's optimal performance and reliability. This includes:

• Chemical process
• Process system
• Chemical safety and environmental protection
• Energy-saving
• Piping and equipment layout

You must consider fluid properties, operating conditions, external environment, economic factors, and relevant regulations, codes, and standards.

Conclusion

Choosing the right valve for industrial applications is a comprehensive process. It involves understanding fluid properties, operating conditions, and flow conditions. Careful consideration and collaboration among engineers ensure the valve's performance and reliability. This guide provides principles and insights to assist in making informed decisions for valve selection in various industrial settings.

FAQs

1. What are the key factors in selecting a valve for industrial use?
   • Key factors include the type of fluid, operating conditions (pressure, temperature, flow rate), material compatibility, valve type, and environmental considerations.
2. How does fluid property affect valve selection?
   • Fluid properties such as toxicity, flammability, corrosiveness, density, viscosity, and phase change conditions determine the appropriate valve material, sealing type, and structural requirements.
3. What is the significance of operating conditions in valve selection?
   • Operating conditions dictate the valve's pressure and temperature ratings, and the valve must be able to handle maximum and minimum values under all possible scenarios, including normal operation, startup, and shutdown.
4. Why is flow condition important for valve selection?
   • Flow conditions such as turbulent flow, two-phase flow, and unstable flow can affect valve performance, cause erosion, cavitation, and noise, and must be considered to ensure reliable valve operation.
5. How can rapid temperature changes impact valve performance?
   • Rapid temperature changes can cause thermal shock, leading to issues like valve jamming, cracking, and seal damage, and should be accounted for in the valve design and selection process.

By addressing these factors, engineers can ensure that the selected valve will perform effectively and reliably under the specified conditions.