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The main manufacturing process of pressure vessel

The manufacturing process of pressure vessels involves several key steps to ensure the vessel’s structural integrity, safety, and functionality. Pressure vessels are containers designed to hold gases or liquids at a pressure significantly different from the ambient pressure. They are commonly used in industries such as oil and gas, chemical, petrochemical, and power generation. Here’s an overview of the main manufacturing process for pressure vessels:

Manufacturing process: The manufacturing process of pressure vessels includes raw material preparation, scribing, blanking, bending of plates, forming, edge processing, assembly, welding, inspection, etc.

Preparation of raw materials

Before marking the steel, the steel must be pre-treated first. The pretreatment of steel refers to the purification treatment, correction, and protective primer coating of steel plates, pipes, and section steels.

Purification treatment

Purification treatment is mainly to remove rust, oxide scale, oil stains, and welding slag on the surface of steel plates, pipes, and sections before scribing, cutting, and welding, and after the steel is cut, beveled, formed, and welded.

  • Degreasing: Remove oils, grease, and other organic contaminants from the steel surface. This step ensures proper adhesion of coatings and prevents defects in welded joints.
  • Pickling: Use an acid solution (typically hydrochloric or sulfuric acid) to remove mill scale, rust, and oxide layers from the steel surface. Pickling cleans the steel and prepares it for further treatments.
  • Rinsing: Thoroughly rinse the steel after pickling to remove residual acid and prevent any adverse reactions with subsequent coatings.
  • Surface Profiling: Create a suitable surface profile (roughness) on the steel to enhance the adhesion of coatings. This step is important for maintaining the integrity of protective coatings.
  • Passivation: Treat the steel with chemicals to create a passive oxide layer on the surface. This layer provides some initial corrosion resistance and prepares the steel for coating.


Rectification is the process of correcting any unintended deformations in steel plates or components that may occur during transportation, hoisting, or storage, ensuring that the materials are properly aligned and in their intended shape for use in pressure vessel manufacturing.

Rectification is an important step in the manufacturing process of pressure vessels. It ensures that the steel plates or components maintain their intended shape and alignment after any potential deformations that might occur during handling, transportation, hoisting, or storage. Properly rectifying the materials is essential to ensure the structural integrity, safety, and performance of the pressure vessel. This process helps prevent issues that could arise from misaligned or deformed components, ensuring that the pressure vessel meets the required specifications and quality standards.

Protective paint

Protective paint is mainly used to improve the corrosion resistance of steel, prevent oxidation, extend the life of parts and equipment, and apply a layer of protective paint on the surface

  • Primer Coating: Apply a protective primer coating to the steel. The primer acts as a barrier against corrosion and prepares the surface for further painting or coating.
  • Drying: Ensure the steel is properly dried after the pretreatment steps to prevent any issues with subsequent processes.


Scribing is the first process in the manufacturing process of pressure vessels. It directly determines the dimensional accuracy and geometric accuracy of the parts after forming and has a great impact on the subsequent assembly and welding processes.

Scribing is drawing the blanking line, processing line, various position lines, and inspection lines on the raw material or the preliminary processed blank, and marking (or writing) the necessary signs and symbols. The marking process usually includes the unfolding, lofting, and marking of parts.

The size of the blank should be determined before scribing.

Scribing is a crucial initial step in the manufacturing process of pressure vessels. It involves marking the raw material or preliminary processed blank with essential lines, signs, symbols, and dimensional information. This precise marking helps ensure the accurate alignment of components during forming, assembly, and welding processes. Here’s a breakdown of the importance of scribing:

Breakdown of the importance of scribing

  • Dimensional Accuracy: Scribing establishes the reference lines and dimensions that guide subsequent manufacturing steps. This accuracy ensures that the pressure vessel components are correctly sized and fit together as intended, reducing the risk of errors in later stages.
  • Geometric Accuracy: The lines and symbols marked during scribing define the exact shapes and positions of various parts. This accuracy is essential for maintaining the pressure vessel’s structural integrity and efficient functioning.
  • Assembly and Welding: Proper scribing ensures that components align precisely during assembly. It provides a visual guide for welders, helping them maintain consistent weld quality and preventing misalignment issues.
  • Unfolding and Lofting: Scribing also includes unfolding complex shapes to flat patterns and lofting, which involves creating templates that guide the forming and cutting of parts. This process streamlines the manufacturing of intricate pressure vessel components.
  • Quality Control: Scribed lines and symbols act as reference points for quality control inspections. They allow inspectors to verify that each step of the manufacturing process conforms to design specifications.
  • Material Optimization: Scribing helps optimize material usage by determining the correct size of the blank needed for each component. This minimizes waste and reduces production costs.

Blank size

The size of the blank is composed of the unfolded size of the part and various machining allowances.

There are mainly the following methods to determine the unfolded size of a part:

  • Drawing method: refers to the use of the geometric drawing method to expand the part into a plane figure.
  • Calculation method: refers to the calculation formula derived according to the principle of expansion or the principle of the constant area before and after compression (drawing) deformation.
  • Test method: It refers to determining the unfolded size of the blank of the more complicated shape part through the test formula. This method is simple and convenient.
  • Comprehensive method: For overly complex parts, drawing and calculation methods can be used for different parts to determine the size of the blank. Sometimes it can also be verified by experimental methods.

Parts for manufacturing containers can be divided into two categories:

Expandable parts and non-expandable parts, such as circular cylinders and elliptical heads, are respectively expandable and non-expandable parts.

Expandable Parts

  • Expandable parts are those components of a pressure vessel that experience significant changes in dimensions (usually expansion) as a result of variations in internal pressure and temperature.
  • Common examples of expandable parts include the cylindrical shell of the vessel and certain types of closures (e.g., dished heads) that are designed to flex and accommodate changes in internal pressure.
  • When the pressure inside the vessel increases, these expandable parts may deform slightly to accommodate the increased volume, helping to maintain the structural integrity of the vessel.

Non-Expandable Parts

  • Non-expandable parts are components of a pressure vessel that do not undergo significant dimensional changes in response to variations in internal pressure or temperature.
  • These parts are usually more rigid and designed to maintain their shape and dimensions under the operating conditions of the pressure vessel.
  • Examples of non-expandable parts include nozzles, manways, support structures, and certain types of flanges or fittings.
  • These parts are typically securely attached to the expandable parts, and their connections are designed to accommodate the relative movements of the expandable components.

Cutting sheet metal

Cutting sheet metal is also called blanking, which refers to the process of separating the required blanks from the scribed raw materials. There are two methods for cutting sheet metal: mechanical cutting and thermal cutting.

Mechanical cutting

Mechanical cutting mainly includes shearing, sawing, milling, and punching, etc. Its characteristic is that mechanical force plays a major role in the cutting process.


Shearing is pressing the scissors into the workpiece to make the shear stress exceed the shear strength of the material to achieve the purpose of shearing. This method has high efficiency and high cutting precision. It can be used as long as the material hardness and size are appropriate, but the metal 2~3mm away from the cut has obvious hardening. According to the plane shape to be cut, it can be divided into straight-line shearing and curve-cutting.

  • Straight cut: Two types of shearing machines use straight long shear blades to cut, namely, flat-cut shears and oblique-cut shears.
  • Shearing machine: In flat shears, the two straight cutting edges are parallel, and the cutting process is carried out simultaneously along the length of the cutting edge, so the shearing force is large and the impact is strong, and it is suitable for cutting thick and narrow strips.
  • Oblique shear: In the oblique shear, the two straight cutting edges are obliquely intersected at a certain angle, and the cutting process is gradually carried out along the length of the cutting edge. Therefore, the shear force is smaller than that of the flat shear when cutting workpieces of the same thickness, and the impact is reduced. It is suitable for shearing. Thin and wide sheets.

In equipment manufacturing, gantry shears are often used to cut linear workpieces. The shearing machine is easy to use, simple to feed, fast in cutting speed, and high in precision.


Sawing is a cutting process, and the equipment used includes grinding wheel saws, circular saws, etc. Sawing is generally used for cutting pipes and profiles.

Thermal cutting

  • Oxygen cutting: Oxygen cutting is abbreviated as gas cutting or flame cutting. Oxygen cutting is thermal cutting. A preheating flame is required for cutting, but the flame alone cannot achieve cutting. The key is to have a high-speed pure oxygen flow.
  • Plasma cutting: Plasma is a state of matter in which all matter is ionized into positive and negative ions. Plasma cutting uses high-temperature, high-speed plasma flame flow to fuse materials to form incisions. It belongs to high-temperature melting and cutting in thermal cutting.

It is not restricted by physical properties. It can cut metals and non-metals, but it is mainly used to cut stainless steel, aluminum, copper, nickel, and their alloys.


Forming of the cylinder

The cylinder body is composed of several cylinder sections welded by circumferential welds, and the cylinder sections are welded by plate rolling and longitudinal welds.

Bending of plates

The principle of the rounding of the barrel section: The rounding of the barrel section is also called bending of plates (plate bending) or plate rolling, which is the basic manufacturing method of the barrel section.

The principle of bending plates is to use a plate bending machine to apply continuous and uniform plastic bending to the steel plate to obtain a cylindrical surface.

Forming of the head

There are three main methods of forming the head: stamping method, spinning method, and explosive forming method.

At present, the commonly used methods are the stamping method and the spinning method.


Welding is a process in which the weldment achieves interatomic bonding by heating or pressurizing, or both, and forming a permanent joint.
The welding process is involved in 50% of the world’s annual steel consumption.

Welding can be divided into three categories: fusion welding, pressure welding, and brazing.

Fusion welding

A processing method in which the workpiece to be welded is locally heated to melt, and then condensed to form a weld to connect the components.

Including arc welding, gas welding, electro slag welding, electron beam welding, laser welding, etc.

Fusion welding is a widely used welding method. Most low-carbon steels and alloy steels are welded by fusion welding. Special fusion welding can also weld non-metals such as ceramics and glass.

Pressure welding

Pressure must be applied during the welding process, which may or may not is heated to complete the welding. The main purpose of the heating is to soften the metal, and the metal is plasticized by applying pressure so that the atoms are close to the distance of mutual attraction. This is essentially different from the heating during fusion welding.

Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosive welding, diffusion welding, and magnetic welding.

Its characteristics are small welding deformation, fewer cracks, and easy automation.


A soldering method in which the solder with a lower melting point than the base material is heated to melt, but the heating temperature is lower than the melting point of the base material, and the molten solder fills the weld, wets the base material, and diffuses with the base material to form an integrated welding method.

Brazing is divided into two categories: hard brazing and soft soldering.

Hard brazing

The heating temperature of brazing is greater than 450°C, and the tensile strength is greater than 200MPa. Silver-based or copper-based solder is often used. It is suitable for occasions with high working stress and high ambient temperatures, such as the welding of cemented carbide turning tools and geological drills.

Soft soldering

The heating temperature of soft soldering is less than 450℃, and the tensile strength is less than 70MPa. It is suitable for environments with low stress and low working temperature, such as tin-based soldering of circuits.

Non-Destructive Testing (NDT)

NDT methods, such as radiography, ultrasonic testing, magnetic particle testing, and dye penetrant testing, are performed to detect any defects in the welds or material.

Key characteristics of NDT include

  • No Damage: NDT methods allow for thorough inspection without causing any harm or altering the material’s properties. This is particularly important when inspecting critical components like pressure vessels, where preserving the structural integrity is paramount.
  • Quality Assurance: NDT is used to ensure that products meet quality standards, helping to prevent defects and identifying any manufacturing irregularities or flaws.
  • Safety Enhancement: By detecting hidden defects or weaknesses in materials or structures, NDT helps enhance safety by preventing potential failures or accidents, especially in safety-critical applications.
  • Cost-Effectiveness: NDT can be more cost-effective than traditional destructive testing methods since it eliminates the need to destroy the tested items for assessment.
  • Diverse Techniques: A wide range of NDT methods exists, each with its specific advantages and limitations. Common NDT techniques include ultrasonic testing (UT), radiographic testing (RT), magnetic particle testing (MT), dye penetrant testing (PT), eddy current testing (ET), and visual testing (VT), among others.

NDT crucial role

  • Weld Inspection: NDT ensures the quality of welds in pressure vessels, detecting any discontinuities that might compromise the vessel’s structural integrity.
  • Material Verification: NDT can verify the material properties and detect inclusions or impurities, ensuring the pressure vessel is made from the correct materials.
  • Defect Detection: NDT can identify cracks, porosity, or other defects that could lead to pressure vessel failure.
  • In-Service Inspection: Throughout a pressure vessel’s operational life, NDT is used to assess its ongoing condition, monitor for potential issues, and make sure the vessel remains safe for use.

Quality Control and Inspection

Inspect the vessel’s welds, surfaces, and overall construction to ensure they meet the design specifications and safety standards.

Dimensional Inspection

Throughout the manufacturing process, various components of the pressure vessel, such as the shell, dished heads, nozzles, and support structures, undergo dimensional inspection.
Precise measurements and checks are conducted to verify that the components adhere to the design specifications, ensuring proper fit and alignment during assembly.

Weld Inspection

Welds in pressure vessels are critical points that must be inspected carefully. Non-destructive testing methods, such as radiographic testing (RT), ultrasonic testing (UT), and magnetic particle testing (MT), are used to examine welds for defects like cracks, lack of fusion, or porosity.
Weld inspection ensures the integrity of the joints, which is vital for preventing leaks or structural failures.

Visual Inspection

Visual inspection is conducted at various stages, including during material handling, fabrication, welding, and final assembly. It identifies visible defects, surface imperfections, or inconsistencies that might impact the vessel’s quality.
Visual inspection ensures that the pressure vessel’s surfaces are clean, free from defects, and meet the required standards.

Final Inspection and Review

Before the pressure vessel is released for use, a final comprehensive inspection is conducted, reviewing all the quality control measures and verifying that the vessel meets the specified requirements.
Qualified personnel review the inspection data and sign off on the vessel’s readiness for service.

Surface Treatment and Coating

Apply protective coatings to the vessel’s interior and exterior surfaces to prevent corrosion or other forms of deterioration.

Final Assembly

Assemble any additional components, such as fittings, valves, nozzles, and supports, as required by the design. Assembling additional components is a crucial step in the manufacturing process of pressure vessels. These components, such as fittings, valves, nozzles, and supports, are essential for the functionality, safety, and connectivity of the pressure vessel within its intended system.

Fittings and Nozzles

Fittings, including flanges, elbows, tees, and reducers, are connected to the pressure vessel to facilitate the flow of fluids or gases.
Nozzles, which are openings in the vessel’s shell or heads, serve as entry and exit points for the process media, as well as for connections to other equipment.
During assembly, these components are precisely positioned and securely welded to the pressure vessel while adhering to design specifications.


Valves control the flow, pressure, and direction of the substances within the pressure vessel.
Depending on the vessel’s purpose, various types of valves, such as ball valves, gate valves, check valves, or control valves, may be installed.
Valves are mounted at appropriate locations, and their connections are carefully sealed to prevent leaks.


Supports are used to hold the pressure vessel in its designated position, especially in cases where the vessel is mounted vertically.
These supports ensure stability, balance, and proper load distribution.
The choice of supports and their installation methods depend on the vessel’s size, weight, and the surrounding environment.

Instrumentation and Accessories

Depending on the specific application and design requirements, additional instrumentation and accessories might be assembled on the pressure vessel.
These can include pressure gauges, temperature sensors, level indicators, relief devices, insulation, and safety features.

Quality Control and Documentation

Each assembly step is carefully monitored to ensure proper alignment, secure connections, and adherence to design tolerances.
Quality control checks are conducted to verify that the assembled components meet the required standards and that there are no defects or leaks.
Detailed documentation of the assembly process, including measurements, welding procedures, and quality inspections, is maintained for record-keeping and future reference.

Testing and Certification

Conduct hydrostatic or pneumatic pressure testing to ensure the vessel can safely withstand the specified pressure.
Pressure Testing: One of the essential inspection processes for pressure vessels is pressure testing. Hydrostatic testing or pneumatic testing is performed to verify that the vessel can withstand the specified internal pressure without leakage or deformation.
Pressure testing is a critical step in confirming the vessel’s ability to safely contain its contents.
Obtain necessary certifications from relevant authorities, such as ASME certification.

Documentation and Compliance

Prepare documentation, including material certifications, welder qualifications, inspection reports, and compliance with applicable codes and standards. Throughout the manufacturing process, detailed documentation of inspections, testing results, and quality control procedures is maintained.
This documentation is essential for traceability, audit purposes, and demonstrating compliance with relevant codes and standards.

Delivery and Installation

Transport the pressure vessel to its intended location, and if necessary, install it in the industrial facility. The delivery and installation of pressure vessels mark the final stages of the manufacturing process. These steps ensure that the pressure vessel is safely transported to its intended location and correctly installed for its intended purpose. Proper delivery and installation are crucial to ensuring the pressure vessel’s functionality, structural integrity, and compliance with safety standards. Here’s an overview of the delivery and installation process for pressure vessels:


Careful planning is essential to transport the pressure vessel from the manufacturing facility to its destination. This involves choosing appropriate transportation methods, such as trucks, rail, or ships, depending on the vessel’s size and destination.
The vessel must be securely loaded, protected from damage during transit, and properly labeled to indicate its contents and any safety considerations.

Unloading and Handling

Upon arrival at the installation site, the pressure vessel must be safely unloaded and handled. This process may require specialized equipment, such as cranes or hoists, depending on the vessel’s weight and size.
Proper handling minimizes the risk of damage to the vessel and ensures the safety of personnel during unloading.

Site Preparation

Before installation, the site must be prepared to accommodate the pressure vessel. This may involve clearing the area, leveling the ground, and ensuring adequate foundation support.
The foundation must be designed and constructed to handle the weight of the vessel and the loads it will experience during operation.

Positioning and Alignment

Accurate positioning and alignment are critical to ensure that the pressure vessel fits properly within the system and aligns with connecting piping and equipment.
Careful measurement and alignment procedures are followed to ensure proper fit and connection of nozzles, fittings, and support structures.

Connection to Piping and Utilities

The pressure vessel is connected to the appropriate piping, utility lines, and other equipment based on the system’s requirements.
Proper connections must be made to ensure the safe and efficient flow of process media into and out of the pressure vessel

Safety Considerations

Safety protocols must be followed during installation, including adherence to industry standards, regulations, and any specific guidelines for the pressure vessel’s operation and maintenance.
All safety devices, relief valves, and protective systems must be properly installed and tested.

Final Inspection and Testing

Once the pressure vessel is installed, a final inspection and testing are conducted to verify that it meets all specified requirements and is ready for operation.
This includes checking connections, performing leak tests, and ensuring that safety systems are functioning correctly.

Documentation and Commissioning

Comprehensive documentation of the installation process, including drawings, test results, and compliance records, is essential for future reference and maintenance.
The pressure vessel is commissioned, and any necessary training for operators and maintenance personnel is conducted.

Final Words

Throughout the entire manufacturing process, safety, quality, and adherence to standards are of paramount importance to ensure the pressure vessel’s reliability in its operational environment.