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Piping Material Selection

The piping material selection process is a critical step in the design of any piping system . The goal is to choose materials that ensure the safe, reliable, and cost-effective transport of fluids while withstanding the operating conditions and environmental factors . Here’s a detailed explanation of the process:

  1. Define Service Requirements:
    • Fluid Type: Identify the fluid(s) to be conveyed, including their chemical composition and physical properties .
    • Operating Conditions: Determine the operating temperature, pressure, and flow rate ranges .
    • Codes and Standards: Identify applicable codes, standards, and regulations (e.g., ASME B31.3, B31.1, API standards) .
  2. Determine Material Properties Required:
    • Corrosion Resistance: Select materials resistant to internal and external corrosion based on the fluid’s corrosivity and the external environment .
    • Strength and Ductility: Ensure materials have adequate tensile strength, yield strength, and ductility to withstand operating pressures and mechanical stresses .
    • Temperature Resistance: Select materials that maintain their strength and integrity at the operating temperature range, considering creep, embrittlement, and thermal expansion .
    • Weldability: If welding is required, choose materials with good weldability to ensure sound joints .
    • Erosion Resistance: For abrasive fluids or high velocities, select materials with good erosion resistance .
    • Thermal Conductivity: Consider thermal conductivity for heat transfer applications or to prevent overheating or freezing .
    • Fatigue Resistance: For systems with cyclic loading, select materials with good fatigue resistance .
  3. Evaluate Material Options:
    • Carbon Steel: A common and cost-effective material for many applications, but susceptible to corrosion in some environments .
    • Stainless Steel: Offers excellent corrosion resistance and high-temperature strength, suitable for corrosive fluids and high-temperature services .
    • Alloy Steel: Used for high-temperature, high-pressure, or specialized applications requiring enhanced strength, creep resistance, or corrosion resistance .
    • Non-Ferrous Metals: Copper, aluminum, and nickel alloys are used for specific applications based on their unique properties (e.g., high thermal conductivity, corrosion resistance) .
    • Plastics: PVC, CPVC, PP, PVDF, and other plastics are used for corrosive fluids, low-pressure applications, and deionized water systems .
  4. Consider Fabrication and Installation Requirements:
    • Welding: Select materials that can be easily welded using standard welding procedures .
    • Formability: Consider the material’s formability for bending, threading, and other fabrication processes .
    • Availability: Ensure that the selected materials are readily available in the required sizes and forms .
  5. Assess Cost:
    • Material Cost: Compare the cost of different materials, considering both the initial cost and the long-term cost of maintenance and replacement .
    • Fabrication Cost: Consider the cost of welding, forming, and other fabrication processes .
    • Installation Cost: Evaluate the ease of installation and any special requirements (e.g., specialized welding procedures, supports) .
  6. Check Industry Standards and Regulations:
    • ASME B31.3: Specifies material requirements for process piping .
    • ASME B31.1: Specifies material requirements for power piping .
    • API Standards: Provide guidelines for material selection in the petroleum and natural gas industries .
    • Local Regulations: Ensure compliance with local building codes and environmental regulations .
  7. Make Final Selection:
    • Document the Selection Process: Document the rationale for selecting the chosen materials, including the factors considered and the alternatives evaluated .

By following these steps, engineers can select the most appropriate piping materials for a given application, ensuring the safety, reliability, and longevity of the piping system .

Articles

Valves Selection

To select a valve, follow these steps while considering the service conditions, valve functions, and cost :

  1. Determine the Valve Function: Decide if the valve will primarily be used for on/off control, throttling, preventing backflow, or specialty purposes such as pressure relief . Different valve types are better suited for specific functions .
  2. Identify Service Characteristics:
    • Fluid Type: Determine if the fluid is a liquid, gas, steam, slurry, or solid .
    • Fluid Properties: Identify if the fluid is clean, dirty, abrasive, corrosive, viscous, or hazardous .
    • Pressure and Temperature: Determine the operating pressure and temperature ranges .
  3. Consider Valve Characteristics: Evaluate application and structural characteristics to ensure proper installation, repair, and maintenance .
  4. Assess Operation and Maintenance Requirements:
    • Fire Resistance: Determine if fire-safe features are needed .
    • Operability: Consider the required speed of operation (e.g., quarter-turn, multi-turn) and actuation method (manual, electric, pneumatic, hydraulic) .
    • Leak Tightness: Determine acceptable leakage rates (internal and external) .
    • Maintainability: Consider ease of access for maintenance and replacement .
  5. Evaluate Valve Types:
    • Gate Valves: Suitable for on/off service with minimal flow restriction .
    • Globe Valves: Used for throttling and on/off service, but with higher flow restriction .
    • Ball Valves: Provide quarter-turn on/off operation with low-pressure drop .
    • Butterfly Valves: Compact and lightweight, suitable for on/off and throttling of large flows .
    • Plug Valves: Offer quarter-turn on/off operation, often used for diverting flow .
    • Diaphragm Valves: Suitable for corrosive or contaminated fluids .
    • Check Valves: Prevent backflow in a piping system .
  6. Consider the Cost: Evaluate not only the initial cost of the valve but also the installation, maintenance, and lifecycle costs .
  7. Check the valve size: Proper valve sizing is crucial for optimal performance. Use valve flow coefficient (Cv) calculations and consult valve manufacturers’ data to determine the correct size .

Articles

Types of Gate valves

Gate valves are classified based on the type of disc, body-bonnet joint, and stem movement . Here’s a breakdown:

I. Based on Disc Type:

  • Solid Wedge Gate Valve: This is the most common and basic type, known for its simplicity and strength . It’s a single, solid piece and suitable for most fluids and turbulent flow .
  • Flexible Wedge Gate Valve: This has a one-piece disc with a cut around the perimeter to provide flexibility . This design is better for thermal expansion and prevents thermal binding, often used in steam systems .
  • Split Wedge (Parallel Disc) Gate Valve: It has two solid pieces held together by a mechanism . This allows each disc to adjust to the seating surface and is suitable for noncondensing gasses and liquids .

II. Based on Body-Bonnet Joint:

  • Screwed Bonnet: This is a simple, inexpensive design .
  • Bolted Bonnet: This is the most common type, using a gasket to seal the joint .
  • Welded Bonnet: It’s a design where disassembly is not required, and it’s lighter than bolted bonnets .
  • Pressure-Seal Bonnet: Used for high-pressure and high-temperature applications, where increased pressure improves the seal .

III. Based on Stem Movement:

  • Rising Stem (Outside Screw and Yoke – OS&Y): The stem rises when the valve is opened, giving a visual indication of the valve position . The stem threads are outside the valve, protecting them from the fluid .
  • Non-Rising Stem (Inside Screw): The stem does not rise or lower; instead, it rotates, making it suitable for tight spaces . The stem threads are exposed to the fluid .

Additional Types:

  • Knife Gate Valve: This is designed with a sharp edge to cut through thick fluids and slurries, often used in industries like mining and paper .
  • Through-Conduit Gate Valve: This type has a gate that’s fully enclosed when open, which is designed to maintain a smooth, uninterrupted flow path. It’s commonly used in pipelines where pigging is required .

Articles

Globe Valves

Globe Valve Types based on Body Bonnet Connection


Screwed bonnet: This is the simplest design available and it is used for inexpensive valves.
Bolted-bonnet: This is the most popular design and used in a large number of globe valves. This requires a gasket to seal the joint between the body and bonnet.
Welded-Bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
Pressure-Seal Bonnet: This type is used extensively for high-pressure high-temperature applications. The higher the body cavity pressure, the greater the force on the
gasket in a pressure -seal valve.

Application of Globe valve
Globe Valves are used in the systems where flow control is required and leak tightness is also important.
It used in high-point vents and low-point drains when leak tightness and safety are major concerns. Otherwise, you can use a gate valve for drain and vent.
It can be used in Feed-water, chemical, air, lube oil and almost all services where pressure drop is not an issue
This valve is also used as an automatic control valve, but in that case, the stem of the valve is a smooth stem rather than threaded and is opened and closed by lifting action of an actuator assembly.

Advantages
Better shut off as compared to gate valve
Good for frequent operation as no fear of wear of seat and disk
Easy to repair, as seat and disk can be accessed from the valve top
Fast operation compares to gate valve due to shorter stroke length
Usually operated by an automatic actuator

Disadvantages
High head loss from two or more right-angle turns of flowing fluid within the valve body.
Obstructions and discontinuities in the flow path lead to a high head loss.
In a large high-pressure line, pulsations and impacts can damage internal trim parts.
A large valve require considerable power to open and create noise while in operation.
It is heavier than other valves of the same pressure rating.
Costlier compared to the gate valve

Articles

Types of Globe Valve

Depending on the type of body there are three types of globe valves;

  • Z types
  • Y types
  • Angle Types

Z types Globe Valve

The simplest design and most common type is a Z-body. The Z-shaped partition inside the globular body contains the seat. The horizontal seating arrangement of the
seat allows the stem and disk to travel at a perpendicular to the pipe axis resulting in a very high-pressure loss.
The valve seat is easily accessible through the bonnet which is attached to a large opening at the top of the valve body. Stem passes through the bonnet like a gate
valve.
This design simplifies manufacturing, installation, and repair. This type of valve is used where pressure drop is not a concern and throttling is required.

Y types Globe Valve

The Y-type design is a solution for the high-pressure drop problem in Z-type valves. In this type, seat and stem are angled at approximately 45° to the pipe axis. Y-body valves are used in high pressure and other critical services where pressure drop is concerned.

Angle types Globe Valve

Angle globe valve turns the flow direction by 90 degrees without using an elbow and one extra pipe weld. Disk open against the flow. This type of globe valve can be
used in the fluctuating flow condition also, as they are capable of handling the slugging effect.

Articles

Gasket Selection (based on ASME)

1. Identify Application Requirements

    • Service Conditions: Determine the operating temperature, pressure, and medium (e.g., gas, liquid, corrosive chemicals) the gasket will be exposed to.
    • Flange Type: Identify the flange design (e.g., raised face, flat face, ring-type joint) per standards like ASME B16.5 or B16.47.
    • Piping or Vessel Code: Confirm the applicable ASME code (e.g., ASME B31.3 for process piping or ASME Section VIII for pressure vessels).

2. Select Gasket Material

    • Compatibility: Choose a material compatible with the process fluid to avoid degradation (e.g., rubber, PTFE, graphite, or metallic materials like stainless steel).
    • Temperature and Pressure Limits: Ensure the material can withstand the maximum temperature and pressure of the system. ASME standards provide guidance on material performance under these conditions.
    • Corrosion Resistance: Consider the environment and potential galvanic corrosion between the gasket and flange materials.

3. Determine Gasket Type

    • Non-Metallic Gaskets (ASME B16.21): Soft gaskets (e.g., rubber, PTFE, compressed fiber) for low-pressure, non-critical applications.
    • Metallic Gaskets (ASME B16.20): Spiral-wound, ring-type joint (RTJ), or solid metal gaskets for high-pressure, high-temperature, or critical services.
    • Semi-Metallic Gaskets: Combination of metal and filler (e.g., spiral-wound with graphite) for versatility in moderate to severe conditions.

4. Size and Dimensions

    • Match the gasket dimensions to the flange size, adhering to ASME B16.20 (metallic gaskets) or B16.21 (non-metallic gaskets). This includes inner diameter (ID), outer diameter (OD), and thickness.
    • Ensure proper fit to avoid overhang or insufficient coverage of the sealing surface.

5. Evaluate Gasket Performance Factors

    • Seating Stress: Calculate the minimum and maximum seating stress required to achieve a seal, using ASME Section VIII, Division 1, Appendix 2. This involves gasket factors “m” (maintenance factor) and “y” (yield factor).
        • m: Ensures the gasket maintains a seal under operating pressure.
        • y: Ensures sufficient initial compression during bolt tightening.
    • Bolt Load: Confirm the bolt load is adequate to compress the gasket without exceeding flange or gasket limits.

6. Consider Design and Installation

  • Flange Surface Finish: Verify the flange surface roughness aligns with gasket type (e.g., smoother finish for soft gaskets, specific serrations for spiral-wound).

Articles

Screw Thread Series

Coarse Thread Series, UNC/UNRC: The coarse thread series UNC/UNRC is the most commonly used thread system used in the majority of screws, bolts, and nuts. It is used for producing threads in low strength materials such as cast iron, mild steel, and softer copper alloys, aluminum etc. The coarse thread is also used for rapid assembly or disassembly.

Fine Thread Series, UNF/UNRF: This is used for applications that require a higher tensile strength than the coarse thread series and where a thin wall is required.

Extra-Fine Thread Series, UNEF/UNREF: This is used when the length of engagement is smaller than the fine-thread series. It is also applicable in all applications where the fine thread can be used.

Unified Standard Series and Selected Combinations, Unified Standard Series: The preferred threads to be used are either the coarse thread series or the fine thread series described above. The fit of screws threads (class 2A/2B and class 3A/3B), as well as the allowances, max and min. major/minor, pitch diameters are described in this table for all the threads, including UNC, UNF, UNEF, UN, UNR series.

Fine Threads for Thin Wall Tubing in the 27 thread series are used for thin wall tubing in the ¼ to 1 inch nominal size. The minimum recommended length of thread is 1/3 of the nominal diameter + 5 threads (+ 0.185 inch). These are included in the Unified Standard Series.

Special Combinations: Thread data are tabulated for certain special combinations of diameter and pitch, with pitch diameter tolerances based on a thread engagement length of 9 x Pitch. The pitch diameter limits are applicable for a length of engagement of 5 to 15 times the pitch. (The length of thread on mating parts, however, may exceed the length of engagement by a large amount) These threads are designated by UNS and UNRS. These are included in the Unified Standard Series.

Articles

Basic Hydrotest requirements

1- Filling pump (high flow rate )

2- Pressure Pump (high head)

3- Manual pump (for small loops)

4- High pressure hose 150 bar

5- Non asbestos sheets

6- Small Fitting ½” ¾”

7- Ball, check & safety valves

8- Pressure gauges

9- Compressor 10 bar

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