Pressure Vessel Terminology Guide
Pressure vessels are a constant in industrial fabrication, and there’s a significant need for clear, consistent pressure vessel terminology. Having concepts applicable to any industry streamlines procurement and ensures everyone speaks the same language regarding safety and compliance.
Below, you’ll find terms and definitions to help you sharpen your technical vocabulary, strengthen team communication and gain confidence in your vessel-related decisions.
Pressure Vessel Terms and Definitions
Understanding pressure vessel definition and industry language can help you hold conversations and interpret contracts and specifications confidently.
These terms govern design, construction, compliance and performance:
1. American Society of Mechanical Engineers (ASME)
ASME is the leading organization responsible for setting the manufacturing standards for pressure vessels in the United States. The ASME Boiler and Pressure Vessel Code (BPVC) provides detailed criteria for materials, design, fabrication, testing and inspection to ensure the safety and reliability of pressure equipment.
2. American National Standards Institute (ANSI)
ANSI is a private organization that supervises voluntary consensus standards for products, services, processes, systems, and personnel in the United States. It accredits standards developed by other organizations, including ASME.
3. Canadian Registration Number (CRN)
A CRN is a unique number issued by a Canadian province or territory that authorizes a pressure vessel to be legally used within its jurisdiction. The number should appear on the tank drawing, data sheet and name plate. Vessels must meet CSA B51 standards, and each design must be registered and approved before manufacturing or use in Canada.
4. Corrosion Allowance
Corrosion allowance refers to the additional material thickness added to a pressure vessel during design to compensate for expected material loss due to corrosion over the pressure vessel’s service life. It ensures the vessel maintains its integrity and pressure capacity despite environmental or chemical exposure.
5. Department of Transportation (DOT)
The U.S. DOT is an official government body that plans, coordinates and oversees federal transportation within the U.S., including the transport of pressure vessels.
6. Design Pressure
Design pressure is the theoretical maximum pressure the system can withstand, given the models available to the designer at the time of design. Maximum allowable working pressure (MAWP) is the highest pressure the system can reach during operation, set below the design pressure to provide a safety margin.
7. Epoxy Lining
Epoxy linings are protective coatings applied inside a tank’s sand-blasted surface to resist corrosion or abrasion. They are common in vessels handling aggressive or hazardous materials and can extend equipment lifespan.
8. Expansion Tank
A pressure vessel is a container designed to hold liquids or gases at a pressure different from the ambient pressure. While some pressure vessels, such as expansion tanks in heating or cooling systems, manage thermal expansion by accommodating volume changes in liquids, other systems operate under different conditions. In certain applications, pressure variations due to environmental factors can vary drastically in pounds per square inch (psi).
9. Filter Tank
A filter tank is a vessel used to house filtration media that separates solids from liquids or gases. These tanks are often mounted in pairs.
10. Heat Cure
This is the process of applying heat to set coatings, resins or linings inside a vessel. A heat cure hardens materials such as epoxy or rubber linings to ensure adhesion and durability under operational stress.
11. Heat Exchanger
A heat exchanger is a device within a tank that facilitates heat transfer between two fluids without allowing them to mix directly. Common types include shell-and-tube heat exchangers and plate heat exchangers.
12. Holiday Test
A holiday test detects pinholes, voids or thin spots in coatings or linings inside a pressure vessel.
13. Hot Water Generator
A hot water generator is used in heating systems to produce hot water using steam or fuel combustion. It’s common in heating, ventilation and air conditioning systems and requires precise temperature and pressure controls to operate safely and efficiently.
14. International Organization for Standardization (ISO)
ISO sets internationally recognized standards that pressure vessel manufacturers often adhere to. These standards ensure consistency, safety and reliability across borders and industries.
15. Joggled Head
A joggled head refers to a head or end cap that has had a lip added to fit snugly within or over the shell. This feature allows for cleaner well seams and can simplify manufacturing alignment.
16. Manufacturer Data Report
The manufacturer data report is a formal document required by ASME that certifies a pressure vessel’s design and construction. It includes material specifications, test results and compliance statements. Data reports are essential for documentation, auditing and regulatory approvals.
17. Maximum Allowable External Pressure (MAEP)
The MAEP is the highest pressure a vessel can withstand during operation on its exterior without breaking or collapsing. This is relevant for vacuum tanks or vessels subject to external pressure because of environmental or process conditions.
18. Maximum Allowable Working Pressure (MAWP)
The MAWP is the highest pressure a vessel can operate under safely. The MAWP is typically signed on the vessel nameplate and should never be exceeded in operation.
19. National Board of Boiler and Pressure Vessel Inspectors
The National Board of Boiler and Pressure Vessel Inspectors oversees equipment registration, inspections and quality control programs. Registering your vessel with the National Board ensures traceability and compliance across jurisdictions.
20. National Sanitary Foundation (NSF)
The NSF is a U.S. certification body that verifies equipment used in food, water and medical applications meets safety and hygiene standards. Vessels carrying NSF certification are recognized for cleanability and materials safety.
21. Pressure Equipment Directive (PED)
PED is a European directive that governs the design, manufacturing and conformity assessment of pressure equipment placed in the European Union market.
22. Pressure Vessel
The general definition of a pressure vessel refers to any container that can hold gases or liquids at a pressure different from ambient pressure. ASME’s pressure vessel definition applies to tanks designed to hold internal or external pressure greater than 15 psi. They can range from small autoclaves to large chemical reactors and must be fabricated under strict regulatory and quality controls.
23. Shell
The shell is the cylindrical main body of the pressure vessel, excluding the head. It can be composed of a variety of materials, such as steel or composites. It bears the majority of the internal pressure and is often the largest component.
24. Stress Relieving
Stress relieving is a post-weld heat treatment process used to reduce residual stresses in welded pressure vessels. This process prevents distortion, cracking and failure.
25. Surge Tank
A type of pressure vessel designed to absorb sudden pressure changes or surges in fluid systems. It helps stabilize pressure, reduce water hammer and protect downstream components from damage.
26. United States Coast Guard (USCG)
The USCG oversees the design and safety compliance of pressure vessels used in marine applications. Pressure vessels installed on ships or offshore rigs often need to meet ASME and Coast Guard standards.
27. Vacuum Tank
A vacuum tank is a vessel designed to operate under negative pressure or vacuum. Often used in storage or degassing systems, vacuum tanks must be manufactured to withstand external pressure.
28. Water Hammer
A water hammer is a pressure surge that occurs when fluid flow is suddenly forced to stop. This transient shock wave can cause damage to pressure vessels, piping and valves, so it should be properly managed with surge tanks.
Why Trust BEPeterson for Pressure Vessel Design and Fabrication?
BEPeterson has over 80 years of experience and has built a reputation for delivering high-performance pressure vessels that meet the requirements for various industries. We’re qualified under ASME Section VIII and hold ISO 9001, TUV and NSF certification.
We custom-engineer every vessel to your unique specifications. Whether you need an ASME-certified tank or a PED-compliant filter vessel, we design and manufacture each unit to match your exact pressure, size, and material requirements.
As a one-stop shop, we handle every stage of the fabrication process in-house. This integrated workflow helps us reduce the inefficiencies that come with outsourcing.
We provide a complete technical package with every project. You get all the documentation you need for regulatory compliance and quality assurance. Each project has a dedicated project engineer who serves as your point of contact throughout the build.
Contact BEPeterson for Your Pressure Vessel Fabrication Needs
For pressure vessel fabrication, you need a partner who understands your application, supports your team and delivers long-lasting products. BEPeterson combines engineering precision, project management and quality control to pressure vessel designs. Our in-house capabilities mean unmatched attention to detail. Request a quote today.