Background – ASME B31.1; 31.3; Piping Code
Keywords: ASME B31.1, ASME B31.1 Power Piping; ASME B31.3; ASME 31.3 Process Piping, ASME B31.4, ASME B31.8
Introduction
The ASME B31 Pressure Piping Code family governs the design, fabrication, and inspection of piping systems across power generation, chemical processing, petroleum refining, and gas transmission industries. While the ASME Boiler & Pressure Vessel Code addresses static equipment like vessels and heat exchangers, the B31 series provides comprehensive requirements for piping systems that transport fluids between process equipment.
Engineers designing power plant steam systems, chemical plant process piping, or pipeline transmission systems must understand which B31 code section applies to their specific application, as each addresses distinct operating conditions, fluid services, and safety considerations. This guide explains the major B31 code sections—including B31.1 (Power Piping), B31.3 (Process Piping), B31.4 (Liquid Pipeline Transportation), and B31.8 (Gas Transmission)—their historical development, scope of application, and the industries that rely on them for safe, compliant piping system design.
When You Need B31 Code Compliance
ASME B31 code compliance becomes mandatory or advisable in numerous situations involving piping system design, construction, modification, and operation. Understanding when these codes apply helps project teams avoid costly redesigns, regulatory issues, and safety concerns.
New Construction and Design Projects
- New piping systems in power plants, chemical facilities, refineries, or industrial plants where jurisdictions have adopted ASME codes
- Projects requiring governmental permits or approvals (EPA, OSHA, state agencies)
- Piping systems connecting to ASME code stamped pressure vessels
Modifications and Expansions
- Adding new branches, tie-ins, or extensions to existing code-compliant systems
- Changing service conditions (pressure, temperature, fluid type) affecting design requirements
- Replacing piping sections where original installation was code-compliant
Jurisdictional and Legal Requirements
- Operating in jurisdictions that have adopted ASME B31 codes into law
- Facilities subject to EPA Risk Management Program (RMP) or Process Safety Management (PSM) regulations
- Insurance company requirements for piping system coverage
Re-rating, Re-certification, and Repairs
- Increasing operating pressure or temperature beyond original design
- Changing fluid service from benign to flammable, toxic, or hazardous
- Permanent repairs to code-compliant piping systems
- Post-incident reconstruction following equipment failures
Explanation of Codes
ASME B31.1 (Power Piping Code) Industries: Electric Utilities, Industrial Power Plants, District Heating Systems, Geothermal Facilities.
Governs piping systems in electric power generating stations, industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems. B31.1 addresses steam, water, and fuel piping operating at elevated temperatures and pressures where failure could impact power generation or facility operations. Power plant engineers, boiler system designers, and industrial facility operators rely on B31.1 for feedwater systems, steam distribution, condensate return, and auxiliary systems throughout power generation facilities.
ASME B31.3 (Process Piping Code) Industries: Chemical Processing, Petroleum Refining, Pharmaceuticals, Oil and Gas Production.
Addresses piping systems in chemical plants, petroleum refineries, and related processing facilities handling diverse fluid services from benign to highly hazardous. B31.3 is the most widely applied piping code, covering everything from normal fluid service to severe cyclic conditions, high-pressure service, and systems handling flammable or toxic materials. Process engineers, plant designers, and EPC contractors use B31.3 for virtually all process piping in chemical plants, refineries, offshore platforms, and pharmaceutical manufacturing facilities.
ASME 31.4 (Pipeline Transportation Systems for Liquid Hydrocarbons) Industries: Oil Pipeline Companies, Petroleum Transportation, Liquid Fuel Distribution.
Covers pipelines transporting liquid hydrocarbons, liquid petroleum products, liquid anhydrous ammonia, and liquid alcohols between production facilities, terminals, refineries, and distribution points. Pipeline engineers and operators use B31.4 for cross-country pipelines, terminal piping, and associated pumping facilities transporting crude oil, refined products, and other liquids over long distances.
ASME B31.8 (Gas Transmission and Distribution Piping Systems) Industries: Natural Gas Transmission, Gas Utilities, Distribution Companies.
Governs gas piping systems from production fields through transmission lines to distribution networks and customer meters. B31.8 emphasizes integrity management, corrosion control, and public safety for systems operating in populated areas and remote locations. Natural gas companies, utility engineers, and pipeline operators apply B31.8 throughout the natural gas supply chain from wellhead to end user.
Each of these codes serves a distinct purpose within the industry, ensuring that piping systems are engineered to meet specific demands while maintaining safety and reliability across various applications. The ASME codes take into account lessons learned from past failures and incidents, incorporating best practices and innovative engineering solutions. By integrating research, industry expertise, and continuous improvements, these codes stay up-to-date with emerging technologies and advancements.
History of ASME B31 Code
In 1926, the American Standards Institute initiated Project B31 to develop a piping code. The first publication was in 1935. From 1942 to 1955 the Code was published as the American Standard Code for Pressure Piping, ASA B31.1. It consisted of separate sections for different industries. Starting in 1955, these sections were split off – and now currently exist as:
- B31.1 Power Piping
- B31.2 Fuel Gas Piping (withdrawn in 1988)
- B31.3 Process Piping
- B31.4 Pipeline Transportation Systems for Liquid Hydrocarbon and Other Liquids
- B31.5 Refrigeration Piping
- B31.6 Chemical Plant Piping (never published – was merged into B31.3)
- B31.7 Nuclear Piping (moved to ASME B&PV Code Section III)
- B31.8 Gas Transmission and Distribution Piping Systems
- B31.9 Building Services Piping
- B31.10 Cryogenic Piping (never published – merged into B31.3)
- B31.11 Slurry Piping
Historically, the initials that have occurred in front of B31.1 have been ASA, ANSI and ASME. In 1978, the Standards Committee was reorganized as a committee operating under ASME procedures with ANSI accreditation – therefore the initials ASME now appear in front of B31.1.
Scope of ASME B31.1 Code
The ASME B31.1 Code was written for power piping systems, covering fuel gas and oil systems in the plant (downstream of the meters), central and district heating systems, in addition to the water and steam systems in power plants.
ASME B31.1 is a consensus document, written by a committee that is intended to contain balanced representation from a variety of interests. Membership includes:
- Manufacturers
- Owners/Operators
- Designers/ Constructors
- Regulatory Agents
- Insurers/Inspectors
- General Interest Parties
B31.1 vs B31.3: Key Differences
While both codes govern piping system design, B31.1 and B31.3 serve distinct industries with different operating philosophies and requirements. Understanding these differences is essential for selecting the appropriate code for your project.
| Aspect | ASME B31.1 (Power Piping) | ASME B31.3 (Process Piping) |
|---|---|---|
| Primary Industries | Electric power generating stations, industrial power plants, geothermal facilities, district heating systems | Chemical plants, petroleum refineries, pharmaceutical facilities, oil and gas production and processing |
| Typical Fluid Services | Steam, water, condensate, fuel oil, fuel gas (power generation focus) | Wide range of fluids including chemicals, hydrocarbons, flammable and toxic materials, corrosive fluids |
| Design Philosophy | Conservative approach focused on long-term reliable operation of power generation systems | Flexible approach accommodating diverse fluid services, from benign to highly hazardous materials |
| Pressure-Temperature Range | Typically high temperature (up to 1000°F+) and moderate to high pressure for steam systems | Broad range from atmospheric to high pressure, ambient to elevated temperatures depending on process |
| Allowable Stress Basis | Generally more conservative allowable stresses, particularly for cyclic service | Allowable stresses vary by fluid service category (normal, Category D, Category M, high pressure) |
| Fluid Service Categories | Not categorized by fluid hazard—uniform requirements apply | Multiple categories: Normal Fluid Service, Category D (non-flammable, non-toxic), Category M (high toxicity), High Pressure Service |
| Flexibility Analysis Requirements | Required for systems subject to thermal expansion, with specific displacement stress range limits | Required for systems that cannot accommodate expansion through layout, with allowable stress range criteria |
| Examination Requirements | 100% radiography for certain welds, extensive visual examination requirements | Examination extent varies by fluid service category—more stringent for Category M, less for Category D |
References
We also Perform ASME Section VIII Design & Analysis on Pressure Vessels, Heat Exchangers and other Process Equipment for Industries including Power, Manufacturing and Petrochemical.
