ANSI appears frequently in industrial standards, but its role is often misunderstood. ANSI stands for the American National Standards Institute, an organization that coordinates the U.S. voluntary standards system rather than directly writing most engineering standards.
In industrial process equipment projects, ANSI often appears alongside ASME, ASTM, API, and ISO, but they play very different roles. This guide explains what is ANSI, what it does, what ANSI standards mean, and how these organizations differ in real industrial applications.
CONTENT:
- What Is ANSI
- What Does ANSI Do
- What Are ANSI Standards and Codes
- What Is the Difference Between ANSI, ASME, ASTM, API, and ISO
- How Are ANSI Standards Used in Oil, Gas, and Petrochemical Projects
- FAQ About ANSI Standards
- Conclusion
What Is ANSI?
ANSI, or the American National Standards Institute, is a private, non-profit organization that administers and coordinates the U.S. voluntary standards and conformity assessment system. It was founded in 1918 and works with industry, government, and other stakeholders across the U.S. standards community.
Unlike ASME, ASTM, or API, ANSI does not directly develop most engineering standards. Instead, it provides the framework through which standards developed by qualified organizations can be approved as American National Standards. This is why many documents associated with ANSI are actually written and maintained by other standards-developing organizations.
What Does ANSI Do
ANSI helps keep the U.S. standards system consistent, transparent, and widely recognized. Its main roles include:
- Accrediting standards developers: Organizations such as API develop standards through ANSI-accredited procedures. API states that its standards are developed through an ANSI-accredited process.
- Approving American National Standards: Qualified standards can gain national recognition after completing ANSI’s consensus, public review, and approval process. Familiar examples include ASME B16.5 and ASME B31.3, both published as American National Standards.
- Coordinating standards development: ANSI helps reduce unnecessary duplication and conflicts between standards developed by different organizations.
- Representing the U.S. internationally: ANSI serves as the U.S. member body in ISO and coordinates U.S. participation in international standardization.
This role is important because it gives industries a common framework for recognizing credible standards, while still allowing organizations such as ASME and API to develop the technical requirements used in real projects.
What Are ANSI Standards and Codes
ANSI standards are more accurately understood as standards approved through the American National Standards process. ANSI does not write these technical requirements itself. Instead, standards developed by ANSI-accredited organizations can be approved as an American National Standard when they meet requirements for openness, balance, consensus, and due process.
ANSI currently oversees more than 13,000 approved American National Standards developed by around 240 accredited standards developers.
Some familiar industrial examples include:
| Standard | Developer | Main Application |
|---|---|---|
| ANSI/ISA-5.1-2024 | ISA | Instrumentation and control symbols widely used in P&IDs and process documentation |
| AWS D1.1/D1.1M | AWS | Structural steel welding requirements for design, fabrication, qualification, and inspection |
| ANSI/AISC 360-22 | AISC | Design and construction requirements for structural steel buildings and other structures |
| ANSI/ASNT CP-189 | ASNT | Qualification and certification requirements for nondestructive testing personnel |
| ASME B31.3 | ASME | Process piping in refineries, chemical plants, hydrogen facilities, and other process plants |
For example:
- ANSI/ISA-5.1-2024 is developed by ISA for instrumentation symbols and identification.
- ANSI/AISC 360-22 is developed by AISC for structural steel design.
- ANSI/ASNT CP-189-2024 is developed by ASNT for NDT personnel qualification.
- AWS D1.1 is likewise published as an American National Standard for structural steel welding.
An ANSI standards list therefore covers standards from many different developers and technical fields, rather than one single family of documents written by ANSI. The developer remains responsible for the technical content, while ANSI approval confirms that the standard has followed the required American National Standards consensus process.
What Is an ANSI Code
You may also see the term ANSI code in engineering documents. A code is not a separate ANSI system. ASME notes that the terms codes and standards are often used interchangeably, and some technical standards are called codes by convention.
For example, ASME B31.3 is formally a process piping code and is also approved as an American National Standard. So, “ANSI code” should not be understood as a separate family of codes written by ANSI.
In practice, the developer, exact designation, scope, and edition are more important than whether the document is called a code or a standard.
What Is the Difference Between ANSI, ASME, ASTM, API, and ISO
Once the role of ANSI is clear, the difference between ANSI, ASME, ASTM, API, and ISO becomes easier to understand. They often appear together in industrial project specifications, but they do not perform the same function.
| Organization | Main Role | Typical Industrial Examples |
|---|---|---|
| ANSI | Coordinates the U.S. voluntary standards system, accredits standards developers, and approves American National Standards | ANSI approval and accreditation across multiple industries |
| ASME | Develops mechanical engineering codes and standards | ASME BPVC, B31.3, B16.5 |
| ASTM International | Develops technical standards for materials, products, test methods, and specifications | Steel plates, pipes, stainless steels, material testing |
| API | Develops standards specifically for the oil and natural gas industry | API 560, API 660, API 661, API 650 |
| ISO | Develops International Standards through a global network of national standards bodies | ISO 9001 and other international engineering and management standards |
Engineering Codes
What Is ASME Code?
Learn how ASME codes define requirements for pressure vessels, boilers, piping, and other mechanical equipment used in industrial projects.
Explore ASME Codes →Heat Exchanger Standards
What Is API 660?
Understand the API 660 requirements for shell-and-tube heat exchangers used in refinery and petrochemical projects.
Explore API 660 →The main difference is therefore one of role and scope. ANSI provides the framework for the U.S. standards system, while organizations such as ASME, ASTM, and API develop the technical requirements engineers use in projects. ISO operates internationally through national standards bodies; ANSI is the official U.S. member of ISO.
ANSI vs ASME
The key difference between ANSI vs ASME is their role in an engineering project. ANSI tells you how a standard gains national recognition; ASME tells you how specific equipment should be engineered and built.
- ANSI: Coordinates the U.S. voluntary standards system, accredits standards developers, and approves eligible standards as American National Standards.
- ASME: Develops the technical codes and standards engineers actually use for mechanical equipment design, fabrication, inspection, testing, and certification.
For process equipment projects, common ASME requirements include:
| ASME Code / Standard | Main Scope | Typical Applications |
|---|---|---|
| BPVC Section I | Power boiler construction | Boilers, steam drums |
| BPVC Section VIII | Pressure vessel design and construction | Separators, reactors, pressure vessels, heat exchangers |
| BPVC Section II | Materials | Pressure-equipment materials |
| BPVC Section V | Nondestructive examination | RT, UT and other NDE |
| BPVC Section IX | Welding qualifications | WPS, PQR and welder qualification |
| ASME B31.3 | Process piping | Refineries, petrochemical and hydrogen plants |
| ASME B16 Series | Flanges, fittings and piping components | Nozzles and piping connections |
| ASME PCC Series | Post-construction practices | Joint assembly, repair and inspection planning |
ASME certification also applies to specific equipment categories. Common examples include U for Section VIII Division 1 pressure vessels, S for Section I power boilers, and H for Section IV heating boilers.
ANSI vs ASTM
The difference between ASTM vs ANSI is especially important when a project involves material selection and procurement.
- ANSI: Provides the framework for developing and recognizing American National Standards.
- ASTM International: Develops the technical specifications and test methods used to define materials, products, and their required properties. ASTM is also recognized by ANSI as an Audited Designator within the American National Standards system.
For process equipment, ASTM requirements commonly appear on material specifications, drawings, and purchase documents:
| ASTM Standard | Main Scope | Typical Applications |
|---|---|---|
| ASTM A516/A516M | Carbon steel plate for welded pressure vessels | Pressure vessel shells, heads, separators and heat exchangers |
| ASTM A240/A240M | Stainless steel plate, sheet and strip | Stainless pressure vessels, tanks and process equipment |
| ASTM A106/A106M | Seamless carbon steel pipe for high-temperature service | High-temperature process and steam piping |
| ASTM A182/A182M | Alloy and stainless steel forgings | Flanges, fittings, valves and other pressure-system components |
ASTM A516, for example, specifically covers carbon steel plate intended primarily for welded pressure vessels, while ASTM A182 covers alloy and stainless steel forgings used for flanges, fittings and other pressure-system components.
ANSI vs API
The key difference between ANSI vs API is scope. ANSI supports the overall U.S. standards system, while API develops technical standards specifically for the oil, gas, refining, and petrochemical industries. API develops its standards through an ANSI-accredited process.
- ANSI: Provides accreditation, coordination, and national standards recognition across many industries.
- API: Develops detailed technical requirements for petroleum-industry equipment, design, fabrication, inspection, and operation.
For process equipment projects, common API standards include:
| API Standard | Main Scope | Typical Applications |
|---|---|---|
| API 560 | Fired heaters for general refinery service | Process heaters and refinery furnaces |
| API 530 | Heater-tube thickness calculation | Fired-heater tubes in petroleum refineries |
| API 660 | Shell-and-tube heat exchangers | Heaters, coolers, condensers and reboilers |
| API 661 | Air-cooled heat exchangers | Refinery, petrochemical and natural-gas service |
| API 650 | Welded tanks for oil storage | Aboveground storage tanks |
Heat Exchanger Basics
What Is a Heat Exchanger?
Explore heat exchanger types, working principles, applications, and key considerations for industrial process equipment.
Explore Heat Exchangers →API’s standards committees cover both fired and unfired heat-transfer equipment, including fired heaters, shell-and-tube heat exchangers, air-cooled heat exchangers, HRSGs and other refinery equipment.
ANSI vs ISO
The key difference between ANSI vs ISO is the level at which they operate.
- ANSI: Coordinates the U.S. voluntary standards system and represents U.S. interests in international standardization.
- ISO: Develops International Standards through a global network of national standards bodies. ANSI is the official U.S. member body of ISO.
For industrial projects, the difference is usually reflected in where the standard is intended to be used:
| Standard System | Main Scope | Typical Project Use |
|---|---|---|
| ANSI / American National Standards | U.S. national standards framework | U.S.-based projects or specifications referencing American standards |
| ISO Standards | International standards | Multinational projects, international procurement, quality and technical requirements |
| ISO standards adopted in the U.S. | International standards accepted for U.S. use | Projects seeking alignment between U.S. and international requirements |
ANSI also coordinates U.S. participation in ISO through U.S. Technical Advisory Groups, which develop U.S. positions on ISO standards and ballots.
How Are ANSI Standards Used in Oil, Gas, and Petrochemical Projects
In real projects, buyers rarely work with one generic “ANSI standard.” A specification usually combines requirements from ASME, API, ASTM, TEMA, and other organizations depending on the equipment and service.
| Equipment / Project Area | Common Standards | Typical Purpose |
|---|---|---|
| Fired Heaters | API 560, API 530 | Heater design and tube-thickness requirements |
| Shell-and-Tube Heat Exchangers | ASME Section VIII, API 660, TEMA | Pressure design, mechanical design and refinery-service requirements |
| Air-Cooled Heat Exchangers | API 661 | Design and fabrication for refinery and petrochemical service |
| Pressure Vessels / Separators / Reactors | ASME Section VIII, ASTM | Pressure-vessel construction and material requirements |
| Storage Tanks | API 650, ASTM | Welded tank design and materials |
| Process Piping | ASME B31.3, ASME B16 Series | Piping design, flanges, fittings and connections |
API, for example, specifically lists API 560 for fired heaters, API 660 for shell-and-tube heat exchangers, API 661 for air-cooled heat exchangers, and API 650 for welded oil-storage tanks. ASME Section VIII covers the design, fabrication, inspection, testing, and certification of pressure vessels.
This is also why terms such as ANSI pressure vessel standards, ANSI heat exchanger standards, or ANSI piping standards can be misleading. The actual technical requirement is usually identified by an ASME, API, ASTM, TEMA, or other specific standard number.
From our project experience at Gelan, the most important step is to confirm the exact standard, edition, equipment scope, and client specification before design begins. This is especially important when one piece of process equipment must satisfy several standards at the same time.
FAQ About ANSI Standards
Are ANSI Standards Mandatory?
No, ANSI standards are generally voluntary. They become mandatory when incorporated into laws or regulations, or when a contract, owner specification, or project requirement explicitly requires compliance.
What Is ANSI Certification?
There is no single general "ANSI certification" for industrial equipment. The term often refers to certification programs or bodies accredited through ANSI/ANAB programs. Equipment-specific certifications, such as ASME U or S certification, are separate and follow their own code requirements.
Is ANSI a Government Agency?
No. ANSI is a private, non-profit organization, not a U.S. government agency. It works closely with government and industry but independently administers the U.S. voluntary standards system.
What Is an ANSI Rating?
"ANSI rating" is an informal industry term commonly used for pressure classes such as Class 150, 300, or 600. For flanges, the actual pressure-temperature ratings are defined by standards such as ASME B16.5 and depend on both material and operating temperature.
What Is an ANSI Flange?
An ANSI flange usually refers to a flange manufactured to dimensions and pressure classes now defined by ASME B16 standards. For example, ASME B16.5 covers pipe flanges from NPS 1/2 through NPS 24, including Classes 150, 300, 400, 600, 900, 1500, and 2500.
What Is ANSI Class 150?
ANSI Class 150 is a pressure class designation, not a maximum pressure of 150 psi. The allowable working pressure varies with flange material and temperature according to the pressure-temperature tables in ASME B16.5.
ANSI B16.5 vs ASME B16.5 — Are They the Same?
"ANSI B16.5" is a legacy industry name; the current standard is ASME B16.5. The B16 standards originated through joint U.S. standardization work, and current ASME B16.5 is published as an American National Standard. They should not be treated as two competing flange standards.
Are DIN and ANSI Flanges Compatible?
Generally, no—DIN/EN and ANSI/ASME flanges should not be assumed to be interchangeable. Modern European flanges typically follow EN 1092-1, while U.S. industrial flanges commonly follow ASME B16.5. Their bolt circles, hole patterns, dimensions, and pressure designations can differ, so compatibility must be checked before connection or an adapter used where necessary.
Conclusion
Understanding what is ANSI makes it easier to distinguish the roles of ANSI, ASME, ASTM, API, and ISO in industrial projects.
Once the applicable standards and project requirements are clear, Gelan can design and manufacture customized process equipment to meet those requirements, including fired heaters, heat exchangers, pressure vessels, and storage tanks.