API 1104 Welding of Pipelines and Related Facilities
API 1104 is the welding code for pipelines and related facilities transporting liquids, gases, or slurries, defining procedure and welder qualification, weld inspection (RT, AUT), and acceptance criteria for cross-country and station piping.
Definition
API 1104 acceptance criteria are based on workmanship for most flaws and on engineering critical assessment (ECA, Annex A) for fatigue-critical situations. Automated UT (AUT) per Annex E is now common for pipeline girth welds, often replacing RT.
What this document is
The API standard for welding of pipelines and related facilities, containing both welding procedure and welder qualification requirements and its own radiographic and ultrasonic acceptance criteria.
How it is applied
Distinctive in that acceptance criteria live in the same document as the welding requirements, and those criteria are length-and-type based rather than the area-based approach found elsewhere. An alternative acceptance annex permits fracture-mechanics-based criteria.
Related documents
API 1104; ASME Section IX where the pipeline code is not the governing authority; ASME B31.4 and B31.8 for the piping systems.
The common misuse
Applying ASME Section VIII acceptance to a pipeline girth weld or vice versa. The criteria are genuinely different, and a weld can pass one and fail the other.
Where API 1104 Welding of Pipelines and Related Facilities fits in an inspection programme
A term is only useful when it connects to a decision. API 1104 Welding of Pipelines and Related Facilities appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
ASME B31.4 Liquid Pipelines — ASME B31.4 is the code for transportation of liquids by pipelines, including crude oil, refined petroleum products, liquid alcohols, ammonia, and CO2, defining weld NDT requirements integrated with API 1104.
ASME B31.8 Gas Transmission and Distribution Piping — ASME B31.8 is the code for gas transmission and distribution piping systems, including pipelines and onshore station piping, defining NDT, hydrostatic testing, and integrity management for natural gas service.
Automated Ultrasonic Testing (AUT) — AUT is the use of mechanized scanners with encoded position to perform ultrasonic inspection (typically PAUT and/or TOFD) with consistent coverage, full data capture, and repeatable scan plans, widely used for pipeline girth welds.
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
API 1104 is the standard governing welding of pipelines and related facilities. It covers welding procedure and welder qualification and the acceptance criteria for the resulting welds, and it is referenced by United States pipeline safety regulation, which makes it the operative welding standard for most transmission pipeline construction.
It is a self-contained system rather than a supplement to the ASME code. Procedure and welder qualification are performed to API 1104's own requirements, with its own essential variables and its own test regime, and a qualification held under ASME Section IX does not automatically transfer. The acceptance criteria are similarly its own — workmanship-based limits on the length and accumulation of imperfections found by radiography or other examination, tuned to the girth welds and field conditions that pipeline construction actually produces. Alongside that workmanship route the standard provides an alternative acceptance approach founded on fracture mechanics, which permits imperfections larger than the workmanship limits where an engineering critical assessment demonstrates they are tolerable for the specific material, geometry, loading and inspection capability. That route is powerful and frequently misunderstood: it is not a relaxation, it is a substitution of analysis and demonstrated flaw sizing for prescriptive limits.
Source: API Standard 1104 Welding of Pipelines and Related Facilities; 49 CFR Part 192 and Part 195 (PHMSA), which incorporate API 1104 by reference for gas and hazardous liquid pipelines respectively; ASME B31.4 and B31.8 for the associated pipeline design codes.
API 1104 compared with the ASME route most fabricators know
Element
API 1104
ASME Section IX with a B31 book
Typical application
Cross-country pipeline girth welds, field construction
Plant piping and pressure equipment
Procedure qualification
API 1104's own essential variables and test regime
Section IX essential variables
Welder qualification
Qualified under API 1104
Qualified under Section IX
Acceptance criteria
Within API 1104, workmanship-based
In the referencing construction code
Alternative acceptance
Fracture-mechanics route with engineering critical assessment
Fitness-for-service assessed separately under API 579
Regulatory status in the US
Incorporated by reference in 49 CFR 192 and 195
Adopted through state pressure equipment programmes
Qualification does not transfer between the two systems. A welder qualified under Section IX is not thereby qualified under API 1104.
Why pipeline welding needed its own standard
Pipeline girth welding is a different problem from shop fabrication. It is performed in the field, in position, at high production rates, on thin-wall large-diameter pipe, frequently with automated or semi-automated processes, and with the whole line depending on the consistency of thousands of nominally identical welds.
A standard built for that reality treats things differently from one built for pressure vessels. The essential variables reflect what actually varies in field production, the qualification tests emphasise the failure modes that field girth welds exhibit, and the workmanship acceptance limits are expressed in terms of imperfection length and accumulation around the circumference rather than area-based criteria suited to shop radiography.
The regulatory adoption follows from that fit. United States pipeline safety regulation incorporates API 1104 by reference, so for regulated pipeline construction it is not one option among several — it is the standard the regulation points at.
The alternative acceptance route, and what it actually costs
The fracture-mechanics acceptance route allows imperfections beyond the workmanship limits when an engineering critical assessment shows they will not compromise integrity. It exists because workmanship limits are deliberately conservative for general use, and on a project with well-characterised material and loading, that conservatism can be quantified away.
The cost is evidence. The assessment needs fracture toughness data for the actual weld and heat-affected zone, a defensible loading spectrum including installation and operational strains, and — critically — a demonstrated flaw sizing capability, because the analysis is only as good as the accuracy with which imperfection height can be measured. That normally means automated ultrasonic testing with a documented sizing qualification, not radiography.
Projects that adopt the alternative route without the sizing qualification behind it have substituted a more permissive number for a more conservative one while keeping an inspection method that cannot measure the parameter the analysis depends on. That is the failure mode worth guarding against.
Where this intersects with in-service inspection
API 1104 governs construction. Once the line is in service, the operative regime is the integrity management requirements of 49 CFR Part 192 or Part 195, with in-line inspection, pressure testing or direct assessment on the reassessment intervals those parts define.
The construction records are the baseline that in-service work depends on: weld maps, radiographs or ultrasonic records, material certifications and as-built wall thickness. An integrity programme that begins at the first in-line inspection run has lost the reference point against which anomaly growth would be measured.
Atlantis works the procedure and personnel layer around this — written practice, NDT procedure development and Level III approval, and independent review of construction data packages before they are relied on. Request a consultation to scope a review.
What does API 1104 cover?
Welding of pipelines and related facilities: welding procedure qualification, welder qualification, and the acceptance criteria for the completed welds. It is referenced by United States pipeline safety regulation, which makes it the operative welding standard for most regulated transmission pipeline construction.
Is an ASME Section IX qualification valid under API 1104?
No. API 1104 is a self-contained system with its own essential variables and test regime, and qualification does not transfer between the two. A welder or procedure qualified under Section IX must be separately qualified under API 1104 for pipeline work governed by that standard.
What is the alternative acceptance criteria route in API 1104?
A fracture-mechanics based approach permitting imperfections larger than the workmanship limits where an engineering critical assessment demonstrates they are tolerable for the specific material, geometry, loading and inspection capability. It substitutes analysis and demonstrated flaw sizing for prescriptive limits rather than relaxing them.
Why does the alternative route usually require ultrasonic rather than radiographic examination?
Because the assessment depends on imperfection height, and radiography measures length well but height poorly. A defensible alternative-criteria project normally uses automated ultrasonic testing with a documented sizing qualification, so the parameter the analysis needs is the parameter the inspection actually measures.
How does API 1104 relate to 49 CFR Parts 192 and 195?
Those parts incorporate API 1104 by reference for the welding of gas and hazardous liquid pipelines respectively. Construction welding is governed by the standard; once the line is in service, the integrity management requirements of the same regulations take over with their own assessment intervals.
Does API 1104 apply to plant piping inside a facility?
Generally no. Process piping within a plant is built to the applicable ASME B31 book with qualification under Section IX and inspected in service under API 570. API 1104 governs the pipeline itself, and the two regimes meet at the facility boundary defined in the regulation.
Frequently asked
Can radiography and ultrasonic examination be used interchangeably under API 1104?
The standard provides for both, with acceptance criteria for each, but they are not equivalent in what they measure. Radiography characterises volumetric imperfections and length well; ultrasonic examination is generally superior for planar imperfections and for height, which is why the alternative acceptance route depends on it.
Who performs the engineering critical assessment?
An engineer competent in fracture mechanics, working from measured toughness data for the actual weld and heat-affected zone and a defensible loading spectrum, with the assessment retained as part of the project record and the inspection sizing qualification attached to it.