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HVAC Systems: Meaning, Objectives, Components, Types, Selection

Written by Anup Kumar Dey in Mechanical,Piping Interface

The full form of HVAC is Heating, Ventilation, and Air Conditioning. Appropriate HVAC provides comfort for people & maintains an effective Environment for surroundings. Proper HVAC Allows humans to exist under adverse conditions. The requirement of HVAC Systems is a must for critical areas like Control rooms, Electronic Equipment Rooms, switchgear halls, Battery rooms, workshop areas, etc. in a petrochemical plant. HVAC systems are designed following basic principles of thermodynamics, heat transfer, and fluid mechanics. The main purpose of the HVAC system is to adjust and change the outdoor air conditions to the desired conditions of occupied buildings for achieving the thermal comfort of occupants. Outside air is drawn inside the buildings and either heated or cooled depending on the outdoor condition. The air is then distributed into the occupied spaces.

Objectives of HVAC Systems

The Primary Intent of HVAC systems is the Comfort of occupants. Other major objectives are

  • Maintaining environmental conditions (temperature and humidity) appropriate to the operating requirements.
  • Increase in Productivity.
  • Building & Equipment Durability.
  • Maintaining pressurization between hazardous and non-hazardous areas.
  • Increase Life & Health.
  • Dilution and removal of potentially hazardous concentrations of flammable/toxic gaseous mixtures in hazardous areas.
  • Filtration of dust, chemical contaminants, and odors through chemical and carbon-activated filters.
  • Inside condition of 21–24°C & 50–60% Relative Humidity is most comfortable & purity of air.
  • The isolation of individual areas and control of ventilation in emergency conditions, through interface with the shutdown logic of the fire and gas detection and alarm safety systems.

However, note that an HVAC system is not intended to prevent catastrophic events such as the release of toxic and/or hazardous gases. Also, HVAC can not compensate on its own, for the intrinsic safety design features such as structural stability, coatings, area segregation, fire protection systems, etc. It only aids the safety process.

HVAC system components

The HVAC system components that condition the air to maintain the thermal comfort of space and occupants and achieve the required indoor air quality are:

  • Air filter
  • Supply fan
  • Mixed-air plenum and outdoor air control
  • Exhaust or relief fans and an air outlet
  • Outdoor air intake
  • Ducts
  • Terminal devices
  • Heating and cooling coils
  • Self-contained heating or cooling unit
  • Return air system
  • Cooling tower
  • Boiler
  • Control
  • Humidification and dehumidification equipment
  • Water chiller

Types of HVAC Systems

There are four major types of HVAC systems available in different sizes. They are:

  • Split HVAC systems
  • Hybrid Heat Split HVAC systems,
  • Duct-free or Ductless HVAC systems, and
  • Packaged heating and air HVAC systems.

Split HVAC Systems:

A split HVAC system is the most common and classic type of HVAC system providing energy efficiency at lower costs. In this model, components are kept both outsides and inside the building and the system is split between two main units, one for heating, and one for cooling. The installation of split HVAC systems is quite complex; So must be performed under expert supervision. Typically, a split HVAC system consists of

  • An outdoor component, or a condenser, such as an air conditioner or a heat pump.
  • An indoor component that consists of an evaporator coil or fan, along with furnaces that convert refrigerant and help circulate air.
  • A system of ducts that circulate air from the HVAC unit throughout the building.
  • A programmable or non-programmable thermostat to manage the system.
  • Accessories like purifiers, air cleaners, UV lamps, or humidifiers improve indoor air quality and comfort.

Hybrid Heat Split HVAC systems:

Hybrid Heat Split HVAC systems are basically an advanced form of split system with improved energy efficiency and lower utility bills. This type of HVAC system typically consists of

  • An evaporator coil and furnaces that work to convert refrigerant and circulate air.
  • A heat pump to cool or heat refrigerant.
  • An oil or gas furnace.
  • Ducts to take the warm or cool air throughout the building.
  • Accessories to improve indoor air quality.

Duct-free or Ductless HVAC systems:

A duct-free or mini-split HVAC system is a unique ultra-efficient HVAC system with large upfront costs. It provides big benefits for certain needs and applications where conventional systems of ducts cannot be used.
Duct-free or ductless HVAC systems consist of the following components:

  • An air conditioner or heat pump to cool or heat refrigerant.
  • Wires and tubes to connect refrigerant from the outdoor unit to the fan coil.
  • A compact fan coil.
  • A thermostat to manage the system.
  • Indoor air quality accessories.

Packaged heating and air HVAC systems:

Packaged heating and air HVAC systems are best suited for buildings without enough indoor spaces for split system components. In such HVAC systems, all components come together in one single package. So, easier to install. But the packed system is outside and exposed to extreme weather conditions, so can be damaged easily. A packaged heating and air HVAC system generally consist of:

  • A heat pump, gas furnace, air conditioner, and the fan coil and evaporator reside in one unit
  • An interface/thermostat on the front of the unit controls the system.
  • Optional indoor air quality accessories.

Depending on the primary equipment location, HVAC systems can be classified as

  • Centralized HVAC Systems and
  • Decentralized or Local HVAC Systems.

The major differences between Centralized and Decentralized HVAC Systems are provided in the following table:

Centralized HVAC systemDecentralized or Local HVAC system
Visually appealing as mechanical equipment is hidden in the mechanical room.Visually not appealing.
Less Flexible.The flexibility of operating different building parts at selected times. Also, flexible to maintain the different temperatures at different building parts.
Less Energy EfficientEfficiency is more.
Higher installation and operating costLower operating and installation costs.
Easy maintenance and Lower maintenance costDifficult to maintain and the cost is higher.
Standby equipment is accommodated for troubleshooting and maintenanceNo backup or standby equipment
Long service lifeReliable equipment, but the estimated service life is normally less.
Centralized vs Decentralized HVAC System

HVAC System Selection

The selection of HVAC systems for a given building depends on various factors as mentioned below:

  • The climate.
  • The shape, size, function, architectural design, and age of the building.
  • The individual preferences of the owner/HVAC designer.
  • Occupant density.
  • The project budget (Initial cost, Operating cost, Maintenance cost, Life-cycle cost)
  • Environmental Impact, Noise, etc.
  • Performance Parameters like Heating capacity, Cooling Capacity, Humidity, Efficiency, Sustainability, Constructibility, Particulate Controls, Ventilation, etc
  • Life Span.
  • Controls.
  • Energy Consumption.
  • Time available for construction.

HVAC system requirements

An HVAC system is primarily based on the following four requirements:

  • Primary equipment
  • Space requirement,
  • Air distribution, and
  • Piping

Primary equipment includes heating equipment (steam boilers/hot water boilers), air delivery equipment (centrifugal fans, axial fans, and plug or plenum fans), and refrigeration equipment (water chillers or refrigerants).

To specify an HVAC system as per design requirements, Space is required for the following facilities:

  • Equipment rooms
  • HVAC facilities
  • Fan rooms
  • Vertical shaft.
  • Equipment access space for installation, replacement, and maintenance.

Air distribution represents the ductwork for delivering the conditioned air to the desired area in a direct, quiet, and economical way. It consists of air terminal units, fan-powered terminal units, variable air volume terminal units, all-air induction terminal units, and air-water induction terminal units. To prevent heat loss and save energy, all the ductwork and piping should be insulated. To host ductwork, buildings should have enough ceiling space.

The piping system is essential to deliver refrigerant, cooled water, steam, hot water, gas, and condensate to and from HVAC equipment in a direct, quiet, and affordable way. Piping systems in HVAC design are normally divided into two parts: the piping in the central plant equipment room and the delivery piping. Depending on the governing code requirement, HVAC piping may or may not be insulated.

How does an HVAC System Work?

Fig. 1 below shows a schematic diagram explaining the basic function of an HVAC system:

Schematic of basic HVAC system
Fig. 1: Schematic of basic HVAC system

Basic Refrigeration Cycle:

Vapour Compression Refrigeration Cycle
Fig. 2: Vapor Compression Refrigeration Cycle

Air Conditioning Capacity – The “Ton”:

  • One Ton of Refrigeration (TR) is defined as the quantity of heat removed to freeze 1 Ton (1 American short ton is 2000 pounds) of water into ice from and at 0°C in 24 hours.
  • 1 Ton of Refrigeration = 12000 Btu/hr or 3024 Kcal/hr

TR = Q x Cp x (Ti – To) / 3024

  • Q = mass flow rate of coolant in kg/hr
  • Cp = coolant specific heat in KCal /kg deg C
  • Ti = inlet, the temperature of the coolant to the evaporator (chiller) in °C
  • To = outlet temperature of coolant from the evaporator (chiller) in °C

Major Work in HVAC (Fig. 3):

  • The design of an HVAC system for plant buildings, requires specific temp., humidity, internal pressure, and cleanliness under various conditions.
  • Preparation of Heat load Calculations, System Diagram, and Duct/Piping Plan.
  • Equipment Sizing & Selection.

HVAC Work Flow:

HVAC System Design
Fig. 3: HVAC System Design

Tools and Products:

E20-II, Elite

  • System Capacity Report (Fan, Cooling, Heating, Humidification)
  • Year Simulation (Power, Operation, Cost)
  • Load Analysis by Each Room
Simulation of HVAC using tools
Fig. 4: Simulation of HVAC using tools

Scope of work:

  • Preliminary Design
  • Vendor Print Checking
  • Engineering
  • Field Engineering

Basic HVAC Equipment:

  • Fans / Blowers
  • Air Handling Units (AHU)
  • Filters
  • Compressor
  • Condensing units
  • Evaporator (cooling coil)
  • Control System
  • Air Distribution System

Common HVAC System Types:

  • Window / Split AC
  • Duct-able Splits
  • Packaged Units
  • Fan Coil Units
  • VRV Units
  • Direct Expansion System
  • Chilled Water System

Split System:

An outline diagram of a typical split system
Fig. 5: An outline diagram of a typical split system

Air Handling Unit (AHU):

Diagram showing an AHU
Fig. 6: Diagram showing an AHU

HVAC Equipment (Fig. 7):

  • Chillers
  • Heat Exchangers
  • Cooling Towers
  • Humidifiers
Diagram Showing Major equipments
Fig. 7: Diagram Showing Major equipment

Air Distribution:

  • Ductwork
  • Metal
  • Flexible
  • Duct board
  • Grilles, Louvers, & Registers
  • Dampers
  • Shut off
  • Fire
  • Smoke
  • Sealants
  • Supports

HVAC Codes and Standards

Various well-established codes and standards that are followed at different stages of HVAC system design are listed below:

  • ISO 15138, Heating, ventilation, and air-conditioning.
  • NORSOK Standard H-001, Heating Ventilation, and Air-conditioning.
  • ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy.
  • ANSI/API RP 500: Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities of Class 1 Division 1 or Division 2.
  • ASHRAE Standard 62.1 – Ventilation for Acceptable Indoor Air Quality.
  • BS 5925: Ventilation principles and designing for natural ventilation.
  • ASHRAE Standard 90.1 – Energy Standard for Buildings Except for Low-Rise Residential Buildings.
  • BS EN 60079-10: Electrical apparatus for explosive gas atmospheres, Part 10. Classification of hazardous areas.
  • IP, Model Code of Safe Practice for the Petroleum Industry: Part 15
  • IS – 12332 For Ventilation in Petrochemical Plants & Refineries.
  • IS – 3103 For Industrial Ventilation.
  • OISD – 163 Safety of Control room for the Hydrocarbon industry.

Online HVAC Courses

The below-mentioned online courses will help to upgrade your knowledge to the next level. So, click on the subject you are interested in learning, review it first, and then enroll if you feel suitable for you:

References:

Compressed Air System: A Detailed Guide

Written by Anup Kumar Dey in Mechanical

Compressed air systems are an essential component in many industrial and commercial operations. They provide a versatile and reliable source of energy that powers various tools and processes.

What is a Compressed Air System?

A compressed air system is a network of equipment designed to convert atmospheric air into a high-pressure source of energy. This system consists of several key components, including air compressors, storage tanks, air treatment equipment, and distribution piping. Compressed air can be used for a multitude of applications, ranging from powering pneumatic tools to actuating machinery and performing process operations.

Why do we need a Compressed Air System?

Compressed Air (CA) is a major prime-mover for the modern industry. Compressed Air is referred to as the fourth utility after electricity, gas, and water. A properly managed Compressed Air system can:

  • save energy
  • reduce maintenance & decrease downtime
  • increase throughput
  • improve product quality depending on its end-use

Compressed Air Quality

Compressed Air quality ranges from Plant air to Breathing air depending upon the end-user. Quality is determined by the dryness & the contaminant level. Higher the quality, the higher the cost. The following figure (Fig. 1) gives the applications of compressed air with respect to quality.

Application of Compressed Air.
Fig. 1: Application of Compressed Air.

Components of a Compressed Air system

Compressed air systems consist of:

  • a supply side which includes compressors and air treatment
  • a demand side, which includes distribution and storage systems and end-use equipment.

A Compressed Air system broadly consists of:

Air Compressor

  • The heart of the compressed air system, the air compressor is responsible for drawing in ambient air and compressing it to a higher pressure. There are several types of compressors, including:
    • Reciprocating Compressors: Utilize a piston mechanism to compress air.
    • Rotary Screw Compressors: Use two interlocking screws to compress air, providing a continuous flow.
    • Centrifugal Compressors: Use a rotating impeller to compress air, suitable for high-capacity applications.

Air Storage Tanks

  • These tanks store compressed air, helping to balance the supply and demand. They allow for peak demand management and reduce the frequency of compressor operation, leading to increased efficiency and extended equipment life.

Air Treatment Equipment

  • To ensure the quality of the compressed air, treatment equipment is necessary. This includes:
    • Filters: Remove dirt, moisture, and other contaminants.
    • Dryers: Reduce humidity in the air to prevent corrosion and other issues in pneumatic tools.
    • Regulators: Control the pressure of the air delivered to various tools and machinery.

Distribution System

  • A network of pipes and hoses transports compressed air from the compressor and storage tanks to the point of use. Proper design and maintenance of this system are critical to minimize pressure drops and energy losses.

Control Systems

  • Advanced compressed air systems may incorporate control systems that monitor and adjust the operation of the compressor, storage, and treatment equipment to optimize performance and energy efficiency.

Air Compressor Types (Fig. 2)

  • The Air compressor is the heart of any CA system.
  • There are two basic compressor types: positive-displacement and dynamic.
Basic Compressor Types
Fig. 2: Basic Compressor Types

Reciprocating Compressor (Fig. 3)

This is a very versatile type of compressor and can be used for nearly all industrial applications. These are constant-capacity machines & deliver the air in pulses.

Characteristics are:

  • High discharge pressures & relatively low to moderate volumetric flows (600-3000 cfm with a pressure range of 2000-5000 PSIG)
  • Generally more maintenance intensive due to the many wearing parts
  • It can be single-acting or double-acting, single-stage or multi-stage, air-cooled or water-cooled and lubricated or non-lubricated.
  • High efficiencies
  • Occupy larger footprint
  • Higher capital cost
  • Control is usually by Load-unload with 3 or 5 step capacity control
A typical reciprocating compressor
Fig. 3: A typical reciprocating compressor

Multi-staging

Multistage machines are used in place of single-stage ones for the following reasons:

  • Single-stage compression would generate excessive heat from compression
  • MOC would have to be of high grade and hence expensive
  • The power consumption of a single machine would be higher
  • Better efficiency

Rotary Compressor (Fig. 4)

The most common type of rotary compressor is the helical-twin, screw type. Less common types include sliding vane, liquid-ring, and lobe.

Characteristics are:

  • Not usually suited for high discharge pressures & are most efficient for moderate air flows & low pressures (3000-6000 cfm with a pressure range of 300-400 PSIG)
  • Low initial cost, compact size, low weight, and easy to maintain.
  • Dry or oil-flooded type
  • Lower efficiency
  • VSDs provide good capacity control
A typical rotary compressor
Fig. 4: A typical rotary compressor

Centrifugal Compressor (Fig. 5)

Centrifugal compressor develops pressure by increasing the velocity of the air going through the impeller & then recovering the velocity in a controlled manner to achieve the desired flow and pressure.

Best suited for continuous air flows in large quantities.

Characteristics are:

  • The heat generated & power consumption is lower.
  • The space requirement & maintenance is minimum.
  • Inherently non-lubricated.
  • Available for flows ranging from 300 to more than 100,000 cfm, but the common ones are 1200-5000 cfm with a pressure range of up to 125 PSIG.
  • Capacity control by inlet valve/guide vane throttling
  • Surge/choke phenomena
A typical Centrifugal Compressor
Fig. 5: A typical Centrifugal Compressor

Characteristic curves

The characteristic curve (Fig. 6) of a compressor plots its discharge pressure as a function of flow.

A typical characteristic curve
Fig. 6: A typical characteristic curve

Selection criteria

  • Flow rate
  • Discharge pressure
  • End-use of the air
  • Energy efficiency
  • Reliability

Compressor sizing

Estimation of Compressed air consumption:

  • Instrument air requirement
    • 5 nm3/hr per CV
    • 0 nm3/hr per ROV
  • The plant (Utility) air requirement
  • Compressed air requirement for pneumatic equipment, etc. operating in full load condition

Compressor Discharge pressure

  • end-use pressure (for instrument air, minimum 7 bar g)
  • plus all the pressure drops in the system.

Compressor Controls

Compressed air system controls serve to match compressor supply with system demand. Proper control is essential to efficient operation & high performance.

System controls include:

  • Start/Stop
  • Load/Unload
  • Dual control
  • Modulating
  • Speed variation
  • Pressure/Flow controls

Minimum Instrumentation required

Indications/alarms/trips consist of 3 major systems: Compressor, Lube oil & Cooling Water

Lube Oil system

 Minimum alarms

  • Low oil pressure
  • Low oil level in the reservoir
  • High oil filter differential pressure
  • High oil temperature
  • The high thrust bearing metal temperature

Temperature gauges

  • Oil piping to & from coolers
  • The outlet of each radial & thrust bearing

Pressure gauges

  • Discharge of the oil pump
  • On bearing header
  • On control oil line & seal oil line

Compressor

  • Pressure indicator at inlet, inter-stage & discharge
  • Pressure switch at discharge
  • Temperature indicator/alarm at inlet, inter-stage, and outlet
  • The temperature gauge on the bearings
  • Vibration switches
  • A safety valve on each stage (for reciprocating type only)
  • Flowmeter (if required)

CW System

  • Pressure & temperature gauge on CW inlet
  • The temperature gauge on CW outlet
  • The thermal relief valve on CW outlet

Contaminants in Compressed air

The 3 major contaminants in Compressed Air are:

  • Water
  • Oil
  • Dirt

Compressed Air System Components/Accessories

The standard components/accessories include:

Prime Mover

The prime mover is the main power source providing energy to drive the compressor. This power can be provided by any of the following sources:

  • Electric motors: Economic, reliable, efficient
  • Diesel/natural gas engines: Fuel availability, higher maintenance, high cost/uncertainty of power
  • Steam turbines & combustion turbines: Inexpensive steam availability

 Intercoolers/Aftercoolers

  • Air-cooled/water-cooled
  • Minimum pressure drop
  • Regular maintenance

 Moisture/oil separators

  • Separation of condensed moisture/oil
  • Types – Impingement baffle type, Centrifugal type, with Demister pads.

 Pulsation Dampeners

  • Reduce/eliminate pulsations of reciprocating machines
  • Installed at the outlet of each stage

 Receivers

  • Storage for utilization at peak load
  • Draining of condensed water
  • Reduce pulsations from reciprocating machines
  • Receiver sizing is based on hold-up for a drop in pressure level, say 10 minutes for a pressure drop of 3 bar.
  • Provided with standard accessories.

 Air filters

Suction filters or Post-compression filters.

Felt cloth filters are used for suction. Compressed air filters can be:

  • Coarse particle filters (filter media can be a ceramic candle, felt cloth, etc)
  • Coalescing & activated carbon filters
  • Microfilter (high efficiency for special uses such as breathing air, etc) Minimum pressure drop

 Drain traps

  • Manual
  • Mechanical float type
  • Electronic timer operated
  • Auto drain traps – condensate sensing
  • Regular maintenance is required to avoid CA wastage

 Lube oil coolers

  • To remove heat from the lube oil
  • Usually Shell & tube type with CW

 Air distribution piping

  • Least pressure drop in the system to reduce operating costs. The maximum pressure drop between the compressor and the farthest end of compressed air consumption should be around 0.3 bar
  • Velocities between 6-10m/s in air mains; this will limit the DP & thus energy consumption and also allow moisture to precipitate
  • Minimum bends & joints (long radius bends to be used)
  • Arrangement for draining of moisture at regular intervals, slope provision
  • Minimum expanders/reducers
  • Leakproof joints, proper piping supports
  • Gauges are to be provided at different locations to monitor the system pressure & temperature.

Compressor Cooling system

Cooling plays an important role in energy efficiency, two types are:

  • Air-cooled – In-efficient, preferred only for low-capacity compressors
  • Water-cooled – Efficient, used for high-capacity compressors

Water is circulated in a jacket around the cylinders to remove the heat resulting from compression & friction due to the sliding of pistons. Water is also required for the inter/aftercoolers and lube-oil coolers.

CW consumption for inter/aftercoolers can be estimated based on the compression ratio per stage assuming an adiabatic efficiency.

Generally, per the thumb rule,

Power Consumption

Compressed air plant layout and distribution

Plant layout:

  • Centralized layout
    • All compressors installed in a single house, cost-effectiveness as maximum plant space utilization
    • More pressure drop expected
  • Decentralized layout
    • Suitable for large industries, different levels/pressures of air
    • Compressor situated at the maximum user location, less pressure drop, max energy utilization
    • This can lead to noise and heat inside the plant

 Compressor location

  • The location should be such that compressor can induct clean, dry, and cool air
  • Interesting fact:- every 4°C reduction in air intake temp reduces power consumption by 1%
  • Points to be remembered while selecting the location of the air compressor:
    • Low humidity to reduce water entrainment
    • Adequate ventilation especially for air-cooled units
    • Minimum suction piping
    • Minimum bends

Compressed air distribution (Fig. 7)

Different compressed air layouts
Fig. 7: Different compressed air layouts

Codes

  • API 617 Centrifugal compressors
  • API 618 Reciprocating compressors
  • API 619 Rotary-type positive displacement compressors
  • API 672 Packaged integrally geared centrifugal air compressors

Applications of Compressed Air Systems

Compressed air systems have a wide range of applications across various industries. Some common uses include:

1. Manufacturing and Assembly

  • Pneumatic Tools: Tools such as drills, wrenches, and hammers are powered by compressed air, allowing for greater efficiency compared to electric counterparts.
  • Material Handling: Compressed air is used in conveyor systems and automated guided vehicles (AGVs) for transporting materials.

2. Food and Beverage Industry

  • Packaging: Compressed air is used for sealing and packaging products, ensuring hygiene and efficiency.
  • Process Control: Many processes in food and beverage production require precise control of air pressure and flow.

3. Automotive Industry

  • Paint Spraying: Compressed air systems are crucial for paint application in vehicle manufacturing, providing a smooth and even coat.
  • Assembly Line Operations: Pneumatic tools are widely used in assembly lines for tasks like fastening and lifting.

4. Healthcare

  • Medical Equipment: Compressed air is utilized in various medical devices, such as ventilators and dental chairs, ensuring reliability and safety.

5. Construction

  • Heavy Machinery: Tools like jackhammers and nail guns rely on compressed air for their operation, improving efficiency on job sites.

Benefits of Compressed Air Systems

Compressed air systems offer numerous advantages that make them a preferred choice for many industries:

1. Versatility

  • Compressed air can power a wide array of tools and equipment, making it suitable for various applications across different sectors.

2. Safety

  • Unlike electricity, compressed air poses minimal fire and explosion risks, making it a safer alternative in hazardous environments.

3. Clean Energy Source

  • When properly treated, compressed air is clean and free from contaminants, making it ideal for applications in sensitive environments, such as food production and pharmaceuticals.

4. Reliability

  • Compressed air systems can provide a consistent and uninterrupted power source, crucial for maintaining productivity in manufacturing and other operations.

5. Energy Efficiency

  • Advanced control systems and energy-saving technologies can help optimize compressed air systems, leading to significant reductions in energy consumption and operational costs.

In conclusion, the compressed air systems are a vital component of many industrial processes, offering versatility, reliability, and safety. Understanding their components, applications, and challenges is essential for optimizing performance and efficiency.

Pressure Vessels: Types, Design, Supports, Applications, Materials

Written by Anup Kumar Dey in Mechanical,Process

What is a Pressure Vessel

A pressure vessel is a closed leak-tight container (normally cylindrical or spherical) designed to hold fluids (i.e, gases, liquids, or two-phase fluids) at a pressure substantially different (higher or lower) from the ambient pressure. They are usually made from carbon steel or stainless steel and assembled from plates by welding method. However, other materials like Aluminium, copper, non-metals, etc also find usage as pressure vessel material in some specific situations. Even though most pressure vessels are basically long cylinders with two heads at both ends, they can take the shape of a sphere or cone.

Examples of some widely used pressure vessels are columns, boilers, separators, knock-out drums, Towers, Bullet Tanks, Reactors, and Heat Exchangers. All these pressure vessels are extensively used in the oil and gas, petroleum refining, and chemical/petrochemical processing industries, and power plants have varying operating pressures and temperatures. However, note that an atmospheric storage tank is not a pressure vessel. Fig. 1 shows a typical pressure vessel used in the oil & gas industry.

What are the Types of Pressure Vessels?

Pressure vessels are classified based on various different parameters which are covered here.

Based on their installation/orientation they are classified into the following two groups.

  1. Vertical pressure vessel
  2. Horizontal Pressure Vessel

Various methods are used to support pressure vessels, like

Types of ends attached to the vessels are

  • Dish ends
  • Conical ends
  • Flat Ends

Fig. 2 shows the general configuration of a pressure vessel.

Typical Pressure Vessels
pressure vessels used in a process plant
Fig. 1: Pressure Vessels used in a process plant

Inputs for the Design of Pressure Vessels

The design of pressure vessels must be done with utmost care as these operate under immense pressure. A ruptured pressure vessel can cause serious irreversible harm to mankind and properties. Normally the ASME Sec VIII code governs the design of pressure vessels.

The following inputs are required for pressure vessel design

Pressure Vessels Design Formula

The basic formula for designing the cylindrical shell is

σ = PD/2t

Therefore,           t = PD/2σ

Where,

  •                 t = thickness of the shell
  •                 P = internal pressure
  •                 D = diameter of the shell
  •                 σ = tensile stress
General Configuration of a typical pressure Vessel
Fig. 2: General Configuration of a Typical Pressure Vessel

This basic formula is modified in international design codes.

For ASME BPVC Sec VIII, the thickness of the cylinder is calculated by the following formula (Fig. 3)

Formula for calculation of pressure vessel shell thickness
Fig. 3: Formula for calculation of pressure vessel shell thickness

Where,

  • t = thickness of the shell
  • P = internal pressure
  • R = radius of the cylinder
  • S = tensile stress
  • E = joint efficiency

Refer to ASME Sec VIII Div 1 for design formulas for all sections of the vessel/cylinder. The following figure provides a typical flow chart for pressure vessel design steps.

Flow Chart for Pressure Vessel Design Steps
Fig. 4: Flow Chart for Pressure Vessel Design Steps

Type of Pressure Vessel Supports

Based on how the pressure vessels are supported, they can be of the following types.

  • Vessel Supported on Lug Support (Fig. 5)
  • Vessel Supported on Skirt(Fig. 5)
  • Vessel Supported on Leg(Fig. 5)
  • Vessel Supported on Saddle(Fig. 6)
types of pressure vessel supports
Fig. 5: Various types of supports for pressure vessel
Pressure Vessel Supported on Saddle
Fig. 6: Pressure Vessel Supported on Saddle

Pressure Vessel Parts

A pressure vessel consists of the following parts

  • Shell, head
  • Nozzles
  • Flanges
  • Gaskets
  • Internals
  • Platforms & ladders
  • Skirt or saddles
  • Baseplate

Click here to know more about major pressure vessel parts.

Design codes used for Pressure Vessel Design

There are various codes that are used for pressure vessel design, construction, and maintenance purposes. Some of them are listed below:

  • EN 13445: The current European Standard, harmonized with the Pressure Equipment Directive (97/23/EC). Extensively used in Europe.
  • ASME Code Section VIII, in addition, is supported by Sections II (materials), V (NDT/NDE), and IX (welding). Published by the American Society of Mechanical Engineers.
  • ASME Code Section VIII Division 1: US standard, design by the formula. Almost exclusively used in North America, widely used worldwide.
  • ASME Code Section VIII Division 2: Alternative Rules, design by analysis.
  • ASME Code Section VIII Division 3: Alternative Rules for Construction of High-Pressure Vessel
  • BS 5500: Former British Standard, replaced in the UK by EN 13445 but retained under the name PD 5500 for the design and construction of export equipment.
  • AD Merkblätter: German standard, harmonized with the Pressure Equipment Directive.
  • EN 286 (Parts 1 to 4): European standard for simple pressure vessels (air tanks), harmonized with Council Directive 87/404/EEC.
  • BS 4994: Specification for design and construction of vessels and tanks in reinforced plastics.
  • IS 2825-1969 (RE1977): code unfired Pressure vessels

Pressure Vessel Internals

Internals are used to separate the liquid from a mixture of liquid & vapor. Refer to Fig. 6

Pressure Vessel Internals.
Fig. 6: Pressure Vessel Internals.

Example of Pressure Vessels

Fig. 7 shows a few of the various types of pressure vessels that are normally used in plants.

various types of pressure vessels in industrial use
Fig. 7: Various types of pressure vessels.

Material of Construction of Pressure Vessel

For industrial applications, the following materials are widely used for pressure vessel construction. However custom-made pressure vessel fabrication is possible depending on requirements.

Applications of Pressure Vessel

Pressure Vessels are most widely used in the following sectors

  • Refinery and Petro-chemical
  • Fertilizer
  • Oil and Gas
  • Chemical
  • Power Plants

Regular inspection of pressure vessels is very important to avoid pressure vessel failures. API 510 provides guidelines for pressure vessel inspection.

The following video provides a comprehensive basic of the pressure vessel design methodologies:

Mechanical Aspects of Pressure Vessel Design

Few more Resources for you.

Brief Explanation of Major Pressure Vessel Parts
A Presentation on VESSEL CLIPS or VESSEL CLEATS
10 points to keep in mind while using project-specific pressure vessel nozzle load tables during stress analysis
Understanding Pressure and Temperature in the context of Pressure Vessel Design
A video tutorial on “Comprehensive Design Code Coverage for Pressure Vessel and Heat Exchanger Design” by Bentley Institute

Reference

https://faculty.washington.edu/vkumar/me356/pv_rules.pdf

Online Course on Pressure Vessels

If you wish to learn more about Pressure Vessels, their design, fabrication, installation, etc in depth, then the following online courses will surely help you:

Several ASME B31 & EN 13480 Issues Needed to Know for Pipe Stress Engineer

Written by Alex Matveev in Piping Stress Analysis,Piping Stress Basics,Start-Prof

Axial Stress from Pressure Load, Axial Force and Torsion Moment

This issue leads to serious under-estimation sustained and expansion stresses in pipes and fittings in ASME B31.1-2018, ASME B31.4-2016, ASME B31.5-2016, ASME B31.8-2016, EN 13480-2017, ISO 14692, and some other codes.

For example, let’s take ASME B31.1-2018 code that requires using the following equation for stress from sustained loads (104.8.1):

The first problem is not so serious for above ground piping. This equation is suitable only for totally unrestrained pipes, but it is easy to use in manual calculations, and it is always conservative. For more information please refer to the article What is Restrained and Unrestrained Pipes. Also in software, the more accurate equation is recommended to use for axial stress 102.3.2 a (3):

Instead of a simplified equation, that is easier for manual calculations

The second and most serious problem is with the formula (104.8.1). It doesn’t take into account axial force in the pipe. Sometimes, the axial force from sustained loads can be so huge, that axial stress becomes greater than allowable. Engineers can easily overlook this problem when using pipe stress analysis software for big models. For example, it could be very tall vertical pipes or heavy valves on the vertical pipes. The code sustained stress for this model is almost zero (see “Sl” stress in the screenshot below). But real sustained stress is greater than allowable (see “Sl*” stress in the screenshot below).

The same problem with the expansion stress equation (104.8.3), it doesn’t include axial force too

For example for totally restrained pipe code expansion stress range will be zero (see “Se” stress in the screenshot below). But real stress range is greater than allowable (see “Se*” stress in the screenshot below).

Sometimes even experienced piping designers can make a mistake and create a wrong design. For example in the piping system below, the 1-2 pipe is restrained by trunnion 2-4. Code stress range is zero, but if we choose the option to include axial force the stress range is greater than allowable!

To protect users from such mistakes we add the special option in PASS/Start-Prof software that allows taking into account stress from the axial force and torsion moment for sustained stress and for expansion stress range. Users can simultaneously see official code stresses (Sl, Se) and modified stress (Sl*, Se*) in the same table. It also automatically solves the first described problem with axial stress from pressure load for restrained, totally unrestrained, and middle behavior systems. Axial stress from pressure load (Sl*) will also be more accurate. This option may be activated using the “Add axial force and torsion stress” checkbox in Project Settings.

For modified stresses PASS/Start-Prof software use the equations similar to ASME B31.3 code:

We recommend always switching this option on!

Effective Tee Branch Section Modulus Issue in ASME B31.3-2016

This issue led to serious under-estimation of sustained and occasional bending stresses at reducing intersections.

ASME B31.1-2018 code requires to calculate the bending stress from thermal expansion for reducing tee branch by equation (all symbols are taken as per ASME B31.3-2016 code for better understanding):

Z is section modulus, where effective branch wall thickness is

 is the thickness of pipe matching branch,

 is the thickness of the pipe matching run of tee or header.

What is the effective branch wall thickness? The answer is given in L.C. Peng’s “Pipe Stress Engineering” book, 4.5.1. The idea is the following. Bending stresses must be checked in two potential locations of failure:

  • In branch and header pipes junction, zone 1
  • in branch pipe next to the junction, zone 2

The failure will happen in zone 1 if the stress intensification factor is high. But if the stress intensification factor is not significant, the failure will happen in zone 2. The code should check the bending stress in both locations.

ASME B31.1-2018 use simplified equation 104.8.3, 104.8.4C:

Where effective branch wall thickness is

For sustained stress equations for 1 and 2 zones should be:

The simplified equation in ASME B31.1-2018 104.8.1, 104.8.4

Now let’s check ASME B31.3-2016 code. As it uses two stress intensification factors (in-plane and out-plane), the equation for bending stress in locations 1 and 2 should be:

But ASME B31.3-2016 code offers for reducing tee bending stress from sustained loads the equation 23b2

Sustained in-plane and out-plane SIFs:

Effective section modulus of branch

Effective wall thickness is determined according to 319.4.4 (c)

If we convert these equations back to the stresses in 1 and 2 locations, we will have

For location 2 stresses become incorrect:

Let’s assume that Mo=0, in this case, we get underestimated by 25% bending stress in the branch pipe

Instead of correct stress value

If we take Mi=0, we get bending stress in the branch pipe

If we assume that io=1.4, then we get bending stress underestimated by 19%

To partially fix this problem we should change the equation 23b2 for effective wall thickness in 320.2 to

But in this case, the out-of-plane bending stress in branch connection will be overestimated. If we assume that io=3.0 the out-of-plane bending stress in branch pipe will be overestimated 25%:

To fix this problem we should correct the bending stress equation in 320.2 to

Zh – Header section modulus, Zb – Branch section modulus.

Unfortunately, these corrections can’t be made in the software. The ASME B31.3 code revision needed.

Fortunately, a new code ASME B31J-2017 has been released. Using this code we can bypass this problem. We recommend activating the “ASME B31J” option in PASS/Start-Prof software.

If this option is activated, the accurate section modulus will be used for header and branch pipes:

Also if “ASME B31J” option is activated then all tees are automatically modeled with simultaneous use of run and branch springs with flexibilities and stress intensification factors calculated according to ASME B31J code requirement:

Start-Prof software allows activating the “ASME B31J” option for all ASME B31 codes and EN 13480! If some of k-factor becomes less than 1.0 Start-Prof assumes this spring as rigid:

Real Bend Wall Thickness is Greater than the Matching Pipe Wall Thickness

This is a very serious issue. It leads to an underestimated pump, nozzle, and support loads and stresses calculated by ASME B31 codes!

ASME B16.9 and all ASME B31 codes don’t regulate the bend, tee, and reducer wall thickness. Only the pipe wall thickness is regulated. So many people think that the elbows and other fittings have the same or almost the same wall thickness as the matching pipe. But in most cases, the real bend, tee, reducer body wall thickness is greater than matching pipe wall thickness with the same Schedule.

For elbows, the real wall thickness can be 10%-40% greater than the matching pipe. Because bends must have greater wall thickness to hold the same pressure as the connected straight pipe (see 304.2.1 3d).

Manufacturers usually produce the bends with a greater wall thickness than matching pipe, but we can get real bend wall thickness only after contacting the manufacturer or even measure it after delivery.

Click to enlarge

Piping designers usually know nothing about it. And piping stress engineers usually use the pipe wall thickness for elbows when using piping stress analysis software. Leaving the “Fitting Thk” field blank makes software thinking that elbow has the same wall thickness as a connected pipe element. This is a serious mistake!

Click to enlarge

According to the ASME B31 and other ASME B31-based codes bend flexibility factor depends on real bend wall thickness, not on matching pipe wall thickness.

The greater bend wall thickness, the greater is bend stiffness (k-factors) and greater are loads on rotating equipment, nozzles, supports and expansion stresses in piping system.

This problem quite often comes to light when Russian companies try to check the design made according to ASME B31 codes for the Russian market. While rechecking the stress analysis using PASS/START-PROF software according to GOST codes a lot of error messages appear. They say that the wall thickness of the elbows is lower than the minimum required one to hold the pressure because it is usually left blank in CAESAR II and software takes fitting thickness equal to connected pipe WT in the piping stress model. When the real elbow wall thickness entered and model recalculated, the nozzle loads and stresses become much greater than it was calculated in CAESAR II and other software! That’s because the elbow flexibility k-factors used during analysis was incorrect.

But in real practice counterparts usually can’t provide the real bend body WT. They just don’t have this information!

We received different answers to the direct question – “what will be the real wall thickness throughout the whole bend body?”

  1. Some manufacturers do not answer at all;
  2. Others say it’s a trade secret (?!);
  3. Some manufacturers replied that the edge will be 100% consistent with that ordered according to ASME (according to schedule), but the thickness of the wall at the bend may even be 40% greater!

Only after we receive the ordered fittings (bends, reducers, and tees) from the factory, only at this time we can measure and find out what are the real wall thicknesses. The stress analysis model should be changed, nozzle loads become greater. The design should be changed to add more flexibility and reduce nozzle loads and sometimes expansion stresses. And all of this should be done after the design job by our contractors was formally “finished”. Amazing!

For example, Russian standards, which are completely different from ASME B16.9 for bends, tees, and reducers, always provide the real body wall thickness for each fitting. Manufacturers follow the standards. Every piping stress engineer knows the real body wall thickness of bends and other fittings and specifies it in START-PROF while performing piping stress analysis. Also, all the bend properties can be taken from the fitting database (see screenshot below).

Click to enlarge

All RD, GOST, and SNiP stress analysis codes (power, process, oil & gas main pipelines, etc.) provide detailed wall thickness calculation procedure for all fittings including bends, tees, and reducers. On screenshots below, you can see that the calculated bend wall thickness is always greater than pipe wall thickness for the same pressure load.

The real bend body wall thickness should be used in piping stress analysis instead of matching pipe wall thickness. To solve this problem we added the special feature in PASS/START-PROF software that allows calculating the approximate “real” bend wall thickness on-the-fly according to ASME B31.3 304.2.1 and the same requirements in other ASME B31 and EN 13480 codes. Just push the button “C” near the “Wall Thickness” field and it will be calculated according to the code requirements.

Conclusion

  1. Bend, tee and reducer wall thickness should be regulated by ASME B31 codes and provided in ASME B16.9 code. Manufacturers should produce bends with body wall thickness according to the code requirements.
  2. Until the first problem is solved, the manufacturers should provide bend wall thickness in their catalogs. It will allow designers and piping stress engineers to use the real WT in the pipe stress model and to get accurate nozzle loads and expansion stresses.
  3. There should be a special remark in ASME B31 codes that explains how to calculate flexibility k-factors for the elbows if the real body wall thickness is unknown.
  4. If the elbow wall thickness is unknown, then piping stress engineers should use WT calculated by ASME B31 code equations for bend or use pipe wall thickness multiplied by 1.4 factor. This will provide more conservative design, and after the real bend, wall, thicknesses will become available (can be measured) the changes in piping design will not be as critical, as now.

To listen directly from the author and learn refer to the following embedded video:

Applicability of Caesar II for stress analysis of lines having D/t ratio more than 100

Written by Anup Kumar Dey in Caesar II,Piping Stress Analysis

Sometimes while working you may have come across situations when the pipe diameter to thickness ratio becomes more than 100. These normally happen for very large-size low-pressure systems. Due to low design pressure (of the order of 1 bar to 3 bar) calculated thickness is less. For example, consider a flare line of 42-inch (or 48 inches) NPS with 3-bar design pressure. The selected thickness is STD wall thickness i.e, 9.525 mm. So the Diameter to thickness ratio is more than 100. Normally Caesar II is widely used for stress analysis of all piping systems. But when you use the software for stress analysis of such stress systems you will find a warning message similar to as shown in Fig. 1. This warning message is generated for all Bend and Intersections in the pipe.

Warning message of Caesar II while stress analyzing line with D/t greater than 100
Fig. 1: Warning message of Caesar II while stress analyzing line with D/t greater than 100

So whether you should proceed with pipe stress analysis ignoring such warning messages. ASME B31.3 does not provide any equation for calculating the SIF values for lines with D/t exceeding 100 (Also known as thin-walled pipes). This restriction on D/t comes from the B31.1 and B31.3 piping codes because they do not have computations for stress intensification factors above this threshold, largely because the testing that was done by Markl had this same limitation. CAESAR II will continue to use the existing code formulations for SIF calculation when a D/t ratio is greater than 100, but no one knows if these relations are still valid. That is the reason Caesar II displays such a warning.

CAESAR II is a pipe flexibility analysis software package and as with all such packages, there are limitations that should not be exceeded. It is always better to use some sort of FEA analysis for analyzing such systems and you will get accurate results. But considering the number of such stress systems in any project (hardly one or two) purchasing costly FEA software may not get the project approval. So in such a situation, you may not have other options than to use Caesar II. So the analyst can use Caesar II, but he needs to always bear the following points in mind:

Failure of thin wall piping is dominated by the buckling phenomenon and the validity of the flexibility analysis assumptions decreases. CAESAR II and other such flexibility analysis programs (CAEPIPE, AUTOPIPE, etc.) do not compute buckling because it is a localized effect caused by imperfections in the manufacture, uneven corrosion, pitting, or other defects. CAESAR II considers the pipe to be homogeneous in cross-section with an even wall thickness everywhere. So the analyst is encouraged to consider buckling separately from the CAESAR II analysis for such systems.

Another problem with the very thin-walled pipe is local deformation in the region of restraint. When significant local deformation is likely at restraint locations, the load distribution will no longer follow expectations as with homogeneous cross-sections and standard flexibility analysis results should not be relied on. Normally it is a standard practice to use wear pads in all support locations to reduce the possibility of local deformation at restraint points.

It is better to use a lowered allowable stress than what is allowed by the piping code in use. For example, the analyst can reduce the allowable value by 75% of the code allowable.

It is better to multiply the Caesar calculated SIF at intersections by 2.5-3.0 and input the same manually at all three node points (Branch and header).

So whether to use Caesar II or not solely depends on the Pipe Stress Engineer. He must discuss the situation with the client and if the client approves then he may proceed with the same. However, recent FEA packages that come along with the latest Caesar II software editions can accurately calculate the SIF values and can be used.

Few more Resources for you..

Stress Analysis Basics
Stress Analysis using Caesar II
Stress Analysis using Start-Prof
Piping Design and Layout

Valve Inspection & Testing | API 598 | Third Party Valve Inspection

Written by Anup Kumar Dey in Engineering Materials,Pipeline,Piping Design Basics

Valve Inspection and Testing is an important subject for piping professionals as it ensures the integrity and performance of Valves during plant operation. During the shutdowns of operating plants, hundreds of valves tend to have various needs to be inspected. Also before use in new plants (during the design phase), the valves must be inspected thoroughly in the manufacturer’s shop to ensure proper quality.

API STD 598- Valve Inspection and Testing provides guidelines for the inspection and testing of valves and the test is conducted by the valve manufacturer. This Valve Inspection article will provide you with some important points related to the inspection of valves and valve testing in the manufacturing shop as well as in operational plants.

Normally the following tests and examinations are performed on Valves/Components.

Valve Inspection and Testing

Shell Test

Required for all valve types. The shell test validates the strength and soundness of the valve pressure-containing structure. This is actually a pressure test where normally air, inert gas, water, kerosene, etc can be used as the test fluid. The minimum shell test pressure that can use are listed in table 2 of API-598. The pressure is applied inside the assembled valve with the ends closed. The valve shall be partially open and be able to hold pressure for a certain time. The pressure shall not be less than 1.5 times of maximum working pressure. No leakage is allowed.

Backseat Test

Required for all valves that have the backseat feature, except for bellows seal valves. This is a feature that allows valve packing to be replaced while it is in service. Normally gate valves, globe, and parallel slide gate valves are subjected to this test. This pressure test is performed to verify leakage past the stem or shaft to the bonnet seal i.e, backseat. Table 3 of API-598 provides the required test pressures for the backseat test for different valve types. In this test, the valve shall be fully opened and the packing gland shall be loose or not installed. No leakage is permissible in the backseat test.

Low-pressure closure test/ High-pressure closure test

Closure tests are performed to confirm leakage past or through a valve’s closure mechanism. The Closure Test or Valve Seat Leak Test is performed after the successful completion of the Valve Body Test/shell test. One side of the valve inlet or outlet shall be subjected to the hydrostatic pressure and the amount of leak shall be measured on the opposite side of the valve.

To explain it, if you are pressurizing the valve inlet, then you have to measure the amount of leakage in the outlet. For both low-pressure and high-pressure tests leakage through the disc, behind the seat rings, or past the shaft seals is not permitted. However, a limited amount of leakage is permissible at the seat-sealing surface interface which is listed in table 5 of API-598.

Double block and bleed (DBB) high-pressure closure test

Pressure shall be applied successively to each side of the closure and Leakage into the body cavity shall be checked.

Visual examination of castings

A visual examination must be performed on all castings to ensure conformance with MSS SP-55.

High-pressure pneumatic shell test

When specified in the purchase order, a high-pressure pneumatic shell test shall be performed. This test shall be performed after the shell test, using appropriate safety precautions. The pneumatic shell test pressure shall be 110 % of the maximum allowable pressure at 38 degrees C (100 degrees F) or as specified in the purchase order. Visible leakage is not allowed.

Table 1 of API 598 specifies the pressure test requirements for various types of Valves. The test equipment should not apply external forces that affect seat or body seal leakage. The following figure shows some sample test equipment used for valve testing.

Valve Test Equipments
Sample Test Equipment

Codes and Standards for Valve Inspection and Testing

Valve inspection and testing must be performed for the smooth and safe operation of industrial processes. Major codes and standards that guide the inspection and testing procedure of a valve are

  • API 598
  • API 607
  • API 6D
  • BS 759

Third Party Inspection for Valves

Third-party valve inspection is normally carried out by the manufacturer, purchaser, and the representative from the third-party inspection agency. Usually, a list of documents is required to be produced before the valve inspector for his review. These documents are:

  • Purchase Order of the Valve
  • Valve Manufacture Quality Control Plan
  • Valve Inspection and Test plan
  • Data Sheet of the Valve
  • All Approved Drawings drawings for the valve
  • Valve Material Test Reports
  • Welding Specification Procedures(WPS) and Procedure Qualification Records (PQR) for the Valve.
  • Valve Welders Qualifications Reports
  • Valve NDE Personnel Qualifications Reports
  • Required NDE Procedures like Dye Penetration, Magnetic Particle, Radiographic, Ultrasonic, PMI Testing, etc. for the Valve.
  • Heat Treatment Procedure of the Valve material.
  • Valve Calibration Certificates for Test Equipment
  • Hydrostatic Testing Procedure of the valve to ensure leak tightness.
  • Closure Testing Procedure, Backseat Testing Procedure, and Water Quality Document
  • Valve Preparation and Painting Procedure
  • Valve Preservation, Packing, and Shipping Procedure
  • Valve Packing List

Valve Material Inspection by Third Party

The original or authenticated copies of valve material mill certificates need to be available with the manufacturer. The representative of the third-party inspector examines these material certificates for compliance with design specifications or drawings. The review includes inspection and checks on:

  • Certificate No.
  • Heat or cast No.
  • Chemical composition.
  • Mechanical properties.
  • Heat-treated condition.
  • NDE applied and results.
  • Surface finish

Valve material includes the body stem material, shell material, valve trim materials, ball, wedge or flap materials, operating components, support material, gland materials, anti-friction materials, well end, flanges, and any other specified component material. Then the inspector witnesses the materials identification on the certificates against the materials marking which is further verified with the valve drawing datasheet, material list, and other specifications.

Upon completion of the valve material inspection by the third part inspector, he issues an inspection visit report (IVR), that contains the following items:

  • Confirmation of satisfactory document review
  • Record of the endorsement of certification reviewed/witnessed
  • Record of all non-conformities
  • Record of any tests witnessed and the result