API 1104 · Pipeline welding

API 1104 weld acceptance explained

Procedure and welder qualification, NDT, and what each acceptance-criteria category evaluates, plus how to read API 5L grades like X52 and X70. Explained in our own words.

Need the acceptance limits? They are in API 1104 itself — API 1104 at api.org →

How an API 1104 job flows, start to finish

Stage	What happens	Paperwork you should have
1. Procedure qualification	A test weld is made and destructively tested to prove the welding procedure works	Qualified WPS + procedure qualification record (PQR)
2. Welder qualification	Each welder makes a test weld tested destructively (or by radiography where permitted)	Welder qualification record, tied to the WPS and its limits
3. Production welding	Welders work within the essential variables of the qualified WPS	Weld log with weld numbers, welder IDs, WPS used
4. Visual inspection	Every weld looked at for profile, undercut, cracks, and fit-up problems	Inspector daily report / weld map
5. NDT	Radiography (RT), ultrasonic (UT), and where called for magnetic particle (MT) or dye penetrant (PT)	NDT reports by qualified technicians, keyed to weld numbers
6. Accept, repair, or cut out	Indications compared to the acceptance standards; defects repaired under a qualified repair procedure or cut out	Repair log, re-inspection reports

Our own summary, not the text of API 1104. Acceptance limits are in the standard itself — use the edition named in your project specification (and the edition incorporated by reference in 49 CFR 192 / 195 for regulated pipelines).

The acceptance-criteria categories, explained (concept only)

Category	What it is	How the standard judges it (in general terms)
Inadequate penetration (IP)	Root not fully filled — the bevel edge is left unfused at the ID	Limits on the length of any one indication and on the total length in a stretch of weld; a separate category covers IP caused by high-low misalignment
Incomplete fusion	Weld metal did not fuse to the bevel face or to a previous bead	Limited by individual and cumulative length, similar in approach to IP
Internal concavity	Root bead fused but sits below the pipe ID surface	Judged by radiographic density compared with the adjacent base metal
Burn-through	Excess penetration blows the weld pool into the pipe bore	Judged by size and by density on the film; cumulative limits apply
Slag inclusions	Non-metallic slag trapped in the weld — elongated or isolated	Separate limits for elongated vs isolated slag, by length, width, and total
Porosity	Gas pockets — scattered, clustered, or hollow-bead along the root	Limits by pore size and by distribution; hollow bead is judged by length
Cracks	A fracture in the weld or heat-affected zone	Treated as a defect with only a very narrow exception for small shallow crater cracks — check the standard
Undercut	A groove melted into the base metal at the weld toe, left unfilled	Limited by depth and by length
Accumulation of imperfections	Many small indications that are each acceptable	A cumulative limit applies across all categories combined

Category names describe what the standard evaluates; the numeric limits are deliberately not reproduced. Our own summary, not the text of API 1104. Acceptance limits are in the standard itself — use the edition named in your project specification (and the edition incorporated by reference in 49 CFR 192 / 195 for regulated pipelines).

Worked example — reading one radiograph for inadequate penetration

Step	Observation	Result
Weld	12 in. girth weld, no high-low misalignment noted	Evaluate under IP (without high-low)
Indication found	One IP indication 1-1/4 in. long	Compare to the individual-length limit
API 1104 limit for a single IP indication	1 in. (25 mm) — from the acceptance standards	Indication exceeds the limit
Disposition	Defect	Repair under a qualified repair procedure (or cut out), then re-inspect

One value used to teach the method. Other categories and the cumulative limits have their own criteria — read them in API 1104.

API 5L grade names decoded

Grade	What the name tells you	Metric name
X42	Specified minimum yield strength (SMYS) of 42,000 psi	L290 (290 MPa)
X52	SMYS of 52,000 psi	L360 (360 MPa)
X70	SMYS of 70,000 psi	L485 (485 MPa)
PSL1 vs PSL2	Product specification level — PSL2 adds tighter chemistry, a maximum yield, and mandatory toughness testing	—

The rule of thumb: the number after the X is the SMYS in thousands of psi; the metric L-number is the same strength in MPa. The same naming runs through the other X grades (X46, X56, X60, X65, X80).

Worked example — what "% of SMYS" means (illustration, not a design calculation)

Input / step	Value	How
Pipe	12.75 in. OD × 0.250 in. wall, API 5L X52	Given
Pressure	1,000 psig	Given
Hoop stress	25,500 psi	P × D ÷ (2 × t) = 1,000 × 12.75 ÷ 0.500
SMYS of X52	52,000 psi	The grade name
Stress level	About 49% of SMYS	25,500 ÷ 52,000

Design pressure for regulated pipelines comes from 49 CFR 192 / 195 (design factors, joint and temperature factors) and the engineer of record — not from this example.

Common field mistakes

Mistake	What to do instead
Welding outside the essential variables of the WPS (diameter group, wall range, position, filler)	Check the qualified ranges before the rig moves — a change may need a new qualification
Weld numbers on the log that don’t match the NDT reports	Assign weld numbers at fit-up and use them on every log, map, and film
Assuming a repaired weld passes because it was ground and re-welded	Repairs must follow a qualified repair procedure and be re-inspected
Using a newer API 1104 edition than the spec or the regulation references	Confirm the governing edition in the contract and in 49 CFR 192.7 / 195.3
Letting welder qualifications lapse between spreads	Track continuity per the spec — see the WPS / welder continuity log

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Pipeline welds, from qualification to sign-off

This page explains API 1104; it does not reproduce its acceptance tables. The standard is published by the American Petroleum Institute (22nd edition, 2021). For regulated gas and liquid lines, the federal rules in 49 CFR Part 192 and Part 195 are public and free to read, and they name the API 1104 edition they incorporate.

Qualification comes first. Before production welding, the contractor qualifies a procedure (a test weld that is destructively tested) and then qualifies each welder on that procedure. Both qualifications have limits called essential variables: pipe diameter and wall ranges, position, direction, process, and filler metal. Most rework on a spread starts when someone welds outside those limits.

NDT and acceptance. Production welds get a visual inspection and then NDT, usually radiography or automated ultrasonic on mainline girth welds. The inspector compares each indication to the acceptance standards for its category. Each category has its own limits on length, size, density, or distribution, and there is also a cumulative limit on all imperfections together. A defect gets repaired under a qualified repair procedure or cut out, then re-inspected. The standard also has an alternative, fitness-for-purpose route (an engineering critical assessment) that applies only when the owner specifies it.

API 5L grades. Line pipe is bought to API 5L. The grade name tells you the strength: the number after the X is the specified minimum yield strength (SMYS) in ksi, so X52 means 52,000 psi and X70 means 70,000 psi. Engineers express operating and test stress as a percentage of SMYS, which is why the grade matters for hydrotest planning.

Keep the records straight with our free weld log template and WPS / welder continuity log. For pipe dimensions, see the steel pipe schedule chart, and for vessel, piping, and tank inspection codes, the API inspection codes guide. Field PM ties weld logs, NDT reports, and photos to the job so the turnover package builds itself.

FAQ

What does API 1104 cover?+

API 1104 covers gas and arc welding of butt, fillet, and socket welds in carbon and low-alloy steel pipe used to transport crude oil, petroleum products, fuel gases, carbon dioxide, and nitrogen. It covers new construction and in-service welding: procedure qualification, welder qualification, inspection and testing, NDT, acceptance standards, and repairs. The current edition is the 22nd (2021).

How is a welder qualified under API 1104?+

The welder makes a test weld using a qualified procedure, and the weld is tested, usually destructively (specimens such as tensile, nick-break, and bend tests) or by radiography where the standard allows. The qualification is limited to the ranges of diameter, wall thickness, position, and process covered by the test. Federal pipeline rules accept qualification under API 1104 or ASME Section IX.

What are the API 1104 acceptance criteria?+

The acceptance standards set limits for each type of imperfection found by NDT: inadequate penetration, incomplete fusion, internal concavity, burn-through, slag inclusions, porosity, cracks, undercut, and accumulated imperfections. For example, a single inadequate-penetration indication (without high-low) longer than 1 inch is a defect. The full limits are in the standard; buy it from API.

What does X52 mean on pipe?+

It is an API 5L grade. The number is the specified minimum yield strength in thousands of psi, so X52 means an SMYS of 52,000 psi. The metric equivalent is L360, the same strength in MPa. PSL2 pipe adds tighter chemistry, a maximum yield, and toughness testing on top of PSL1.

Which edition of API 1104 do I use?+

Use the edition your project specification names. For DOT-regulated pipelines, 49 CFR 192.7 and 195.3 list the edition incorporated by reference, which can lag behind the newest API edition. When the spec and the regulation differ, raise it with the owner before welding starts.

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