6.1 Inadequate Penetration (IP), IP Due to High-Low (IPD) & Cross Penetration (ICP)
Key Takeaways
- Inadequate Penetration Without High-Low (IP, 9.3.1) is the incomplete filling of the weld root; it is a defect when an individual indication exceeds 1 in. (25 mm) or the aggregate exceeds 1 in. (25 mm) in any continuous 12 in. (300 mm) of weld.
- Inadequate Penetration Due to High-Low (IPD, 9.3.2) occurs when misalignment leaves one root edge unbonded; limits are 2 in. (50 mm) individual and 3 in. (75 mm) aggregate per 12 in.
- Inadequate Cross Penetration (ICP, 9.3.3) is a subsurface lack of bond between the first inside pass and the first outside pass; limits are 2 in. (50 mm) individual and aggregate per 12 in.
- For welds shorter than 12 in. (300 mm), the IP aggregate may not exceed 8% of the total weld length.
- Radiographically, IP appears as a sharp dark line centered on the root pass, while IPD shows the dark line offset to one side against a density step from the misaligned walls.
6.1 Inadequate Penetration (IP), IP Due to High-Low (IPD) & Cross Penetration (ICP)
Root-pass penetration defects are among the most heavily examined acceptance rules in API 1104. The 22nd edition splits them into three classifications in Section 9.3: Inadequate Penetration Without High-Low (IP, 9.3.1), Inadequate Penetration Due to High-Low (IPD, 9.3.2), and Inadequate Cross Penetration (ICP, 9.3.3).
1. Definitions and Formation
IP — Inadequate Penetration Without High-Low (9.3.1)
IP is the incomplete filling of the weld root: weld metal failed to fill the root channel, leaving unfilled root face(s) at the inside surface. One or both root faces may be inadequately filled. Causes: insufficient heat input, excessive travel speed, root land too thick or root gap too narrow, wrong electrode angle, or an electrode too large for the joint.
IPD — Inadequate Penetration Due to High-Low (9.3.2)
IPD exists when one edge of the root is exposed (unbonded) because adjacent pipe or fitting joints are misaligned. The recessed wall's root face never melts into the bead. Causes: pipe out-of-roundness, wall-thickness mismatch without proper transition, poor lineup clamp practice, or premature clamp release.
ICP — Inadequate Cross Penetration (9.3.3)
ICP is a subsurface lack-of-bond imperfection between the first inside pass and the first outside pass — the two passes never fused through the vertical land faces. It is characteristic of joints welded from both sides (e.g., some tie-ins and repair configurations) and cannot be seen on either surface.
2. Radiographic Signatures
| Defect | Radiographic appearance |
|---|---|
| IP | Sharp, dark, continuous or intermittent line centered in the root-pass image |
| IPD | Dark line along one side of the root image, next to a light/dark density step from the offset walls |
| ICP | Subsurface dark line or band mid-wall at the root, between the two pass images |
3. Acceptance Limits (22nd Edition)
| Defect | Individual length | Aggregate length per continuous 12 in. (300 mm) | Short welds (< 12 in.) |
|---|---|---|---|
| IP (9.3.1) | > 1 in. (25 mm) = defect | > 1 in. (25 mm) = defect | Aggregate > 8% of weld length = defect |
| IPD (9.3.2) | > 2 in. (50 mm) = defect | > 3 in. (75 mm) = defect | (no separate 8% clause) |
| ICP (9.3.3) | > 2 in. (50 mm) = defect | > 2 in. (50 mm) = defect | (no separate 8% clause) |
Critical CWI note: for IP, the individual and aggregate limits are the same 1 in. Two 0.6 in. IP indications in one 12 in. segment total 1.1 in. and reject the weld even though each passes individually.
4. Worked Evaluations
Example 1 — IP aggregation (12 in. segment)
Two IP indications, 0.6 in. and 0.5 in., in one 12 in. segment. Individuals: 0.6 ≤ 1.0 OK, 0.5 ≤ 1.0 OK. Aggregate: 0.6 + 0.5 = 1.1 in. > 1.0 in. → REJECTED.
Example 2 — IPD aggregation
Two IPD indications, 1.8 in. and 0.9 in., in one 12 in. segment. Individuals ≤ 2.0 OK. Aggregate 2.7 in. ≤ 3.0 in. → ACCEPTED.
Example 3 — Short weld, 8% rule
A 2.375 in. OD nipple: weld circumference = π × 2.375 ≈ 7.46 in. One IP indication of 0.70 in. Individual OK (≤ 1.0). But 8% × 7.46 = 0.597 in., and 0.70 > 0.597 → REJECTED under the short-weld rule.
5. Inspection Governance Around These Limits
- Section 9.1: the acceptance standards apply to imperfections located by RT, MT, PT, and UT — and may also be applied to visual inspection. NDT may not be used to select which welds or specimens go to destructive testing under 6.5.
- Section 9.2 (Rights of Rejection): every NDT method is limited in what its indications reveal, so the company may reject ANY weld that appears to meet the acceptance standards if, in its opinion, the depth of an imperfection may be detrimental to the weld.
- Measurement convention: when an indication's size is measured, the maximum dimension of the indication is applied to the criteria.
- Base material imperfections (9.3.13): imperfections found in the base material or seam welds during radiography are reported to the company, which directs their disposition — they are not scored against weld acceptance limits.
6. Prevention Through Fit-Up and Root-Pass Control
Acceptance limits tell the inspector when to reject; production control keeps IP, IPD, and ICP out of the weld in the first place.
- IP prevention: the WPS joint design specifies bevel angle, root face, and root opening with tolerances (5.3.2.4). A root face left too thick or a root gap closed below tolerance starves the arc; an oversized electrode, insufficient current, or excessive travel speed produces the same unfilled root. Verifying the line-up and running the root pass inside the qualified heat-input range are the primary controls.
- IPD prevention: IPD is a fit-up defect before it is a welding defect. Holding high-low within the 1/8 in. (3 mm) alignment limit of 7.2, keeping the lineup clamp in place until the WPS-specified percentage of the root bead is complete, and matching or taper-transitioning pipes of different wall thicknesses all protect the recessed root face from being skipped by the arc.
- ICP prevention: because ICP forms between passes deposited from opposite sides of the joint, two-sided welds such as tie-ins and some repair configurations depend on each side’s first pass penetrating fully through the land; back-gouging to sound metal before welding the second side removes the risk entirely.
- Detection correlation: radiography can understate root conditions on small-diameter or heavy-wall pipe, which is why qualification nick-breaks and bends remain the proof of root soundness — a tight IPD line against an offset wall can hide inside the density step between the two wall thicknesses on film.
Under API 1104:2021 Section 9.3.1, what is the maximum allowable aggregate length of Inadequate Penetration Without High-Low (IP) in any continuous 12-inch weld length?
What are the individual and aggregate limits for Inadequate Penetration Due to High-Low (IPD) under API 1104:2021 Section 9.3.2?
A production girth weld has a total length of 8.0 inches. Radiography shows a single IP indication of 0.75 inches. What is the disposition under Section 9.3.1?