Welding Codes and Standards: AWS, ASME and API Explained

AWS, ASME, and API welding requirements cover different types of work, and choosing the right one starts with the component being built rather than the welding process alone. AWS D1.1 is a major structural-steel welding code, ASME codes cover pressure vessels and many piping systems, and API standards address specific petroleum and pipeline applications such as API 1104 and API 650. Project specifications, materials, service conditions, jurisdiction, and the adopted edition determine what actually governs.

Which Welding Code Do You Need?

Selecting the correct welding code depends first on what is being designed or fabricated. AWS codes are widely used for structural work, ASME codes govern many pressure vessels and piping systems, and API standards address defined petroleum, storage-tank, and pipeline applications.

The American Welding Society provides structural welding requirements such as AWS D1.1/D1.1M. ASME separates construction requirements from qualification requirements: pressure-vessel rules are found in the Boiler and Pressure Vessel Code, while BPVC Section IX addresses qualification of welding, brazing, and fusing procedures and personnel when the applicable construction code invokes it. API documents such as API Standard 1104 establish requirements for welding pipelines and related facilities within their defined scope.

Each document has its own material limits, qualification rules, inspection provisions, acceptance criteria, and documentation requirements. A pressure vessel may require ASME Section VIII together with Section IX and Section V; process piping may invoke ASME B31.3 plus Section IX; a building frame may be governed by AWS D1.1; and a transmission pipeline may use API 1104 when specified by the project or applicable regulation.

Correct selection promotes compliance and safety, reduces avoidable weld rejection, and gives engineers, fabricators, inspectors, and owners a common acceptance basis before fabrication begins. Equipment capability still matters, and a capable multi-process welder can support several processes, but machine capability never overrides the governing code, qualified procedure, or project specification.

Current Edition Snapshot

Standards change regularly, so edition numbers should always be verified before a project starts. As of September 2026, the organizations list the following current or recently published documents relevant to this comparison:

AWS Welding Codes for Structural Steel

AWS D1.1 is a primary code for structural steel welding. It establishes requirements covering areas such as design, fabrication, welding procedures, welder qualification, workmanship, inspection, and acceptance of welds in carbon and low-alloy structural steels within its scope. AWS currently lists D1.1/D1.1M:2025-AMD1.

The code has historically been intended for commonly used structural carbon and low-alloy steels at or above its minimum thickness limit. However, material eligibility should be checked directly against the governing edition rather than reduced to a simple yield-strength grouping. The 2025 edition, for example, introduced ASTM A913 Grade 80 as a prequalified base metal in a new strength category.

Prequalified WPS vs WPS Qualified by Testing

AWS D1.1 makes an important distinction between a prequalified Welding Procedure Specification and a procedure that must be qualified by testing. If all requirements for prequalification are satisfied, a contractor can prepare a compliant prequalified WPS without producing a supporting Procedure Qualification Record for that WPS. When prequalification conditions are not met, procedure qualification testing is required and the resulting PQR supports the WPS.

• A written WPS tells the welder how the production weld must be made.
• A prequalified WPS is permitted only when all applicable prequalification conditions are satisfied.
• A test-qualified WPS is supported by procedure qualification testing and a PQR.
• Welder or welding-operator performance qualification is separate from procedure qualification.
• Inspection verifies that workmanship and completed welds meet the governing acceptance requirements.

This distinction matters because “WPS required” does not automatically mean “PQR required for every WPS.” Training equipment is also a separate issue: choosing suitable welders for beginners can help people learn a process, but production work still has to follow the qualified or prequalified procedure required by the governing code.

AWS D1.6/D1.6M applies separately to structural stainless-steel assemblies, so D1.1 should not be treated as the universal AWS code for every structural metal.

ASME Codes for Pressure Equipment

Where AWS D1.1 is focused on structural steel, ASME codes are central to pressure-containing equipment where failure can release stored energy or hazardous process media.

The ASME Boiler and Pressure Vessel Code contains multiple sections that work together. Section VIII provides rules for construction of pressure vessels. Division 1 is the widely used ruleset for pressure-vessel construction, while Division 2 provides alternative rules with different design margins, analysis methods, materials, fabrication, examination, testing, and certification requirements. Division 2 should not be described simply as the option for “higher pressure.” Division 3 addresses high-pressure vessels within its own specialized scope.

ASME Section IX addresses qualification of welding, brazing, and fusing procedures and personnel. It does not by itself provide the complete design and construction rules for a pressure vessel or piping system. Instead, a construction code such as Section VIII or an ASME B31 piping code references Section IX where its qualification rules are required.

ASME B31 Piping Codes

The B31 series covers different types of pressure piping rather than one universal piping application. ASME B31.1 covers power piping in applications such as power-generating stations and certain industrial or institutional plants. ASME B31.3 covers process piping commonly found in refineries, chemical plants, pharmaceutical facilities, hydrogen facilities, semiconductor plants, and related processing installations.

ASME projects therefore often combine several documents. A pressure-vessel fabricator may need Section VIII for construction, Section IX for welding qualification, Section V for nondestructive examination methods where invoked, and Section II for material information. A piping project may similarly use a B31 construction code together with Section IX qualification requirements.

Welder selection and equipment duty cycle remain practical shop considerations, especially for processes such as GTAW, but a TIG welder is suitable for ASME work only when the machine, process variables, consumables, procedure, personnel qualifications, and production weld all comply with the governing requirements.

API Welding Standards for Oil and Gas

API publishes standards and recommended practices for many petroleum and related applications, but there is no single “API welding code” that covers every oil-and-gas weld.

API Standard 1104

API Standard 1104, Welding of Pipelines and Related Facilities, provides requirements for gas and arc welding used in construction and in-service repair of piping and components within its pipeline scope. The 22nd Edition was published in 2021, and API’s standards plan records Addendum 1 to that edition as published on September 3, 2026.

API 1104 includes its own provisions for procedure qualification, welder qualification, production welding, inspection, nondestructive testing, acceptance standards, and repair within the applications it covers. Those requirements should not be assumed to match AWS D1.1 or ASME Section IX simply because all three address welding qualification.

API Standard 650

API Standard 650, Welded Tanks for Oil Storage, establishes requirements for welded storage tanks within its scope. API published the 14th Edition in August 2025. Tank projects may also reference ASME Section IX for welding procedure and performance qualification as required by API 650, illustrating why different standards can work together on one project.

API RP 577 and API RP 582

API Recommended Practice 577 provides guidance on welding processes, inspection, and metallurgy for inspectors and others working with refinery and chemical-plant equipment. API Recommended Practice 582 supplies supplementary welding guidelines for chemical, oil, and gas industry equipment. These are recommended practices; they do not automatically replace the construction code or standard governing the equipment.

• Reliable welds help protect personnel, assets, and the environment.
• Inspection and NDE requirements must follow the governing document rather than being borrowed from another code.
• Material compatibility, welding variables, heat treatment, and examination requirements depend on the service and construction standard.
• Machine choice is only one part of compliance. Even capable welders for home use should not be assumed suitable for code production work without confirming process capability, qualification requirements, and project specifications.

AWS vs ASME vs API: Key Differences

The clearest way to compare AWS vs ASME vs API welding codes is by asking what is being built, which document controls construction, and where welding qualification requirements come from.

AWS D1.1 centers on structural steel construction and includes its own welding procedure, qualification, workmanship, and inspection framework. ASME pressure-equipment projects commonly separate construction requirements from Section IX qualification rules. API documents target defined petroleum-industry applications such as pipelines or welded storage tanks.

The governing code follows the component and service—not the welder’s preferred process or machine.

Acceptance requirements also differ. That does not mean one code family is inherently “stricter” or “more flexible” than another. Each document establishes criteria for the risks, materials, weld types, examination methods, and service conditions within its own scope.

All three families rely on controlled welding procedures, qualified personnel where required, inspection, and documentation, but they use different qualification systems and acceptance rules. Understanding MIG welder performance may help with equipment selection, but code compliance ultimately depends on the permitted process, WPS variables, consumables, personnel qualification, inspection, and project requirements.

How to Choose the Governing Welding Code

Use the following sequence before preparing a WPS or starting fabrication:

1. Identify the component. Determine whether the work is a building structure, bridge component, pressure vessel, power piping, process piping, transmission pipeline, storage tank, or another type of equipment.
2. Check the contract and drawings. Look for a stated construction code, welding standard, owner specification, engineering specification, and required edition.
3. Confirm material and service. Material grade, thickness, temperature, pressure, cyclic loading, corrosion environment, and fluid service can change the applicable requirements.
4. Identify referenced qualification documents. A construction code may send you to another document, such as ASME Section IX, for procedure and personnel qualification.
5. Verify regulatory adoption. Confirm whether an authority having jurisdiction or applicable regulation requires a particular code edition, inspection method, certification, or documentation package.

Can More Than One Welding Code Apply?

Yes. Large facilities often contain components governed by different code families. A refinery, for example, may have process piping designed and fabricated to ASME B31.3, pressure vessels constructed to ASME Section VIII, storage tanks built to API 650, structural steel governed by AWS D1.1, and certain pipeline systems governed by API 1104.

Even one component can rely on several documents. An ASME pressure-vessel project can use Section VIII for construction, Section IX for welding qualification, Section V for NDE methods when referenced, and Section II for material properties and specifications. API 650 likewise interacts with referenced welding-qualification requirements rather than functioning in isolation.

When requirements overlap, do not combine the most convenient provisions from different codes. Follow the hierarchy established by the governing construction code, project specification, contract documents, and authorized engineering decisions.

Frequently Asked Questions

What are the differences between AWS and ASME welding standards?

AWS D1 codes such as D1.1 are construction-oriented welding codes for specific structural materials and applications. ASME pressure-equipment codes divide responsibilities among documents: Section VIII covers pressure-vessel construction, B31 codes cover specific piping systems, and Section IX provides procedure and personnel qualification rules when referenced. Neither family is universally stricter; they address different equipment and risks.

What does API stand for in welding?

API stands for the American Petroleum Institute. API publishes standards and recommended practices used in petroleum, natural-gas, pipeline, refining, and related industries. For welding, commonly referenced documents include API 1104 for pipelines and related facilities, API 650 for welded oil-storage tanks, and recommended practices such as API RP 577 and RP 582.

What is the API code for welding?

There is no single API document for every welding application. API Standard 1104 is the key welding standard for pipelines and related facilities within its scope. API 650 contains welding requirements for welded oil-storage tanks, while other API standards and recommended practices apply to other types of equipment.

What are the AWS standards for welding?

AWS publishes many welding codes, specifications, and standards rather than one universal welding standard. Examples include AWS D1.1 for structural steel, D1.2 for aluminum structures, D1.3 for sheet steel, D1.4 for reinforcing steel, D1.6 for stainless-steel structures, and D1.8 as a seismic supplement to D1.1 for applicable seismic-force-resisting systems.

Is ASME Section IX a construction code?

No. ASME Section IX focuses on qualification of welding, brazing, and fusing procedures and personnel. The construction requirements for the finished equipment come from the applicable construction code, such as ASME Section VIII for pressure vessels or an ASME B31 code for piping.

Can AWS and ASME requirements apply on the same project?

Yes. A facility can contain AWS-governed structural steel alongside ASME pressure vessels and piping. The codes normally apply to different components, and the contract or engineering specification should identify which document controls each part of the project.

Should I always use the newest welding-code edition?

Not automatically. Standards organizations publish new editions and amendments, but a contract, owner specification, regulation, or authority having jurisdiction may adopt a specific earlier edition. Verify the governing edition before changing a WPS, qualification record, inspection plan, or acceptance criterion.

Conclusion

Selecting the correct welding code is a matter of component scope, service conditions, contractual requirements, and regulatory adoption rather than personal preference. AWS D1.1 is a key structural-steel code; ASME Section VIII, Section IX, and B31 documents divide construction and qualification responsibilities for pressure equipment and piping; and API documents such as 1104 and 650 address specific pipeline and storage-tank applications. Before welding starts, confirm the governing document, edition, material scope, WPS requirements, personnel qualifications, inspection methods, and acceptance criteria. That preparation reduces rework and helps ensure the finished weld meets the requirements actually applicable to the project.

Sources

1. American Welding Society — AWS D1.1/D1.1M Structural Welding Code—Steel — current D1.1 scope, qualification, inspection, and edition information.
2. American Welding Society — AWS D1.6/D1.6M Structural Welding Code—Stainless Steel — structural stainless-steel scope and current AWS listing.
3. ASME — 2025 Boiler and Pressure Vessel Code — current BPVC edition and applicable sections.
4. ASME — BPVC Section IX — welding, brazing, and fusing qualification requirements.
5. American Petroleum Institute — API Standard 1104 — pipeline welding scope and 22nd Edition information.
6. American Petroleum Institute — Standards and Product Updates — API 650 14th Edition and related current-publication updates.