Complete Joint Penetration (CJP) Weld — D1.1:2025 Guide
A complete joint penetration weld extends through the full 板厚 of the 母材 joint. Under D1.1:2025, 事前認定 CJP groove joints per Clause 5.4.1 and Figure 5.1 require no PQR. Non-prequalified CJP procedures must be qualified by 試験 per 表 6.2.
What Is a CJP Weld?
A complete joint penetration (CJP) 開先溶接 is a weld in which the 溶接金属 extends through the full thickness of the joint. The weld fuses completely from one surface to the other, creating a joint with the same cross-sectional 強度 as the base metal itself.
CJP welds are required wherever the joint must carry the full design load of the connected members. In 構造用鋼, this includes moment connections in rigid frames, heavy bracing connections, column splices in seismic applications, and any joint where the engineer specifies full-strength performance. When a connection must transmit tension perpendicular to the weld axis, a CJP weld is typically the only option that satisfies D1.1 strength 要求事項 without a reduced 有効のど厚 calculation.
The defining characteristic of a CJP weld is not the groove type — it is the completeness of fusion. V形開先, bevel, J形開先, U形開先, and even 角形開先 welds can all achieve CJP when the weld metal fully penetrates the joint thickness. What matters is that no root area remains unfused.
Key distinction: CJP is defined by the 結果 (full penetration), not the method. The same V-groove joint can produce a CJP weld when backgouged and backwelded, or a PJP weld when welded from both sides without backgouging (Clause 5.4.2).
CJP vs PJP — When Each Applies
The distinction between CJP and PJP under D1.1 is defined by how the weld is executed, not just the 継手形状. Clause 5.4.1 governs CJP groove welds. Clause 5.4.2 defines PJP groove welds as groove welds without steel バッキング welded from one side, and groove welds welded from both sides but without backgouging.
| Attribute | CJP | PJP |
|---|---|---|
| Penetration | Full joint thickness | Partial — specified depth |
| Effective throat | Equals base metal thickness | Reduced — per Table 5.8 minimum |
| D1.1 clause | Clause 5.4.1 | Clause 5.4.2 |
| Prequalified details | Figure 5.1 | Figure 5.2 |
| Typical use | Moment connections, column splices, tension joints | Shear connections, stiffener welds, compression splices |
| Design strength | Full base metal strength | Must be calculated based on effective throat |
The engineer selects CJP when the connection must develop the full strength of the members. PJP is appropriate where the applied loads are less than the full capacity of the connected parts — and where the reduced effective throat is accounted for in design calculations. PJP welds are generally less expensive to produce because they require less weld metal and may not require backgouging.
Prequalified CJP Groove Joints
D1.1:2025 Clause 5.4.1 defines prequalified 完全溶込み開先溶接 details. CJP groove welds that match the configurations in Figure 5.1 may be used without performing the WPS qualification test described in Clause 6. This means no PQR, no 試験溶接, and no 破壊試験 — provided every element of the procedure stays within the prequalified envelope.
Figure 5.1 contains dozens of prequalified CJP joint details organized by groove type: single-V, double-V, single-bevel, double-bevel, single-U, double-U, single-J, double-J, and square groove. Each detail specifies the ルート間隙, 開先角度, ルート面 dimension, and whether backing is required. The dimensions are given as ranges with tolerances — the “As Detailed” column shows the design values, and the “As Fit-Up” column shows the acceptable variations per Clause 5.4.1.8.
To use a prequalified CJP joint, all of the following must be satisfied:
- Joint detail matches Figure 5.1
- The groove type, root opening, groove angle, and root face must match one of the prequalified configurations. Joint dimensions may vary within the tolerances shown in the “As Detailed” column per Clause 5.4.1.1.
- Approved 溶接 process
- The process must be SMAW, SAW, GMAW (except GMAW-S short-circuit transfer), or FCAW. These are the only four prequalified processes under Clause 5.
- Approved base metal and filler metal
- The base metal must be listed in Table 5.6 and matched with an approved 溶加材 per Table 5.7. 確認 your steel against Table 5.6 using your mill test report. Using a base metal not in Table 5.6 disqualifies the prequalified path entirely.
- Preheat and interpass temperature
- Minimum 予熱 must meet Table 5.11 requirements for the base metal カテゴリー, 溶接工程, and material thickness.
A typical structural building frame using A992 steel with single-V CJP joints, E71T-1 FCAW wire, and parameters within Clause 5 限界値 qualifies entirely under the prequalified path. No PQR required.
CJP welds in cyclically 読み込み済み connections may require UT or RT examination in addition to 外観検査 by a CWI. Where the Engineer specifies it, PWHT requirements may apply per D1.1 Section 7.8 depending on base metal and service conditions. D1.1 Clause 5.4.1 also provides prequalified welding procedures for common CJP groove configurations — V-groove, bevel, J-groove, and U-groove — that eliminate the need for separate 資格試験.
Backgouge and Backing Requirements
Backing and backgouging are among the most frequently misunderstood aspects of CJP welding. D1.1 does not require backing on every CJP weld — the requirement depends on whether the weld is made from one side or two.
When Backing Is Required
Clause 5.4.1.2 states that prequalified CJP groove welds made from one side only shall have steel backing. This is the default for single-sided CJP joints in Figure 5.1. The バッキングバー provides a surface for the ルートパス and helps achieve full penetration without 溶落ち.
When Backing Is Not Required
CJP welds do not always require backing. Clause 5.4.1.3 permits prequalified CJP groove welds without steel backing when two conditions are met: the backing is removed after welding, and the back side of the weld is backgouged to sound metal and backwelded. Double-sided CJP welds — where the joint is welded from both sides with backgouging — achieve full penetration without any permanent backing.
Backgouging removes the root of the first-side weld to expose sound weld metal, eliminating any lack-of-fusion or slag inclusions at the root. The backweld then completes the joint from the second side. This technique produces a CJP weld with no permanent backing bar embedded in the joint.
Practical note: Many engineers prefer backgouged CJP welds for fatigue-sensitive connections because the backing bar removal eliminates a potential stress concentration at the 溶接ルート. The choice between backed and backgouged CJP depends on access, cost, and fatigue requirements — not a blanket 基準 requirement.
How to Qualify a CJP WPS
When a CJP groove weld falls outside the prequalified limits of Clause 5 and Figure 5.1, the WPS must be qualified by testing per Clause 6. Table 6.2 defines the number and type of test specimens required for CJP groove weld qualification, along with the range of thickness qualified.
The qualification test involves producing a test weld on plate (or pipe for tubular applications), extracting specimens, and performing destructive testing. For plate tests, Table 6.2 specifies 目視試験 (VT) per Clause 6.10.1, reduced-section tension tests, and either root and face bend tests or side bend tests depending on plate thickness. The plate thickness tested determines the range of base metal thickness qualified for production welding.
For plates 3/8 in and under, the test qualifies a 最小 thickness of 1/8 in and a 最大 of 2T (twice the test plate thickness). For plates over 1 in, the minimum remains 1/8 in and the maximum is unlimited. This means a single test on 1 in plate qualifies the procedure for all thicknesses from 1/8 in upward.
The essential variables recorded on the resulting PQR define the boundaries of the qualified WPS. Any change to an 重要変数 listed in Table 6.6 — welding process, 溶加材分類, 母材群, position, preheat, or any of the other 35 listed variables — may require re-qualification.
How CJP Appears on a Welding Symbol
On engineering drawings, a CJP weld is indicated by showing the groove 溶接記号 (V, bevel, J, U, or square) without a depth dimension in the 溶接サイズ position on the 基線. When no weld サイズ (depth) is specified, the weld is understood to be complete joint penetration. If a depth dimension appears — such as “3/8” next to a V-groove symbol — the weld is PJP to that depth.
The groove angle, root opening, and root face dimensions appear in their 規格 positions on the 溶接記号表示. If backing is required, the backing symbol (a rectangle on the opposite side of the reference line) is included. A tail note may specify the WPS number, welding process, or other supplementary information.
For a deeper dive into welding symbol conventions, see our groove weld symbol reference and complete symbol chart.
Frequently Asked Questions
No. D1.1:2025 Clause 5.4.1.2 requires steel backing for prequalified CJP groove welds made from one side only. However, Clause 5.4.1.3 permits CJP welds without steel backing when the backing is removed after welding and the back side of the weld is backgouged to sound metal and backwelded. Double-sided CJP welds with backgouging do not require backing at all. The backing requirement applies specifically to single-sided prequalified CJP joints.
CJP (complete joint penetration) means the weld metal extends through the full thickness of the joint. PJP (partial joint penetration) means the weld metal does not extend through the full thickness. Under D1.1:2025, the distinction depends on how the weld is made: groove welds without steel backing welded from one side, and groove welds welded from both sides but without backgouging, are considered PJP per Clause 5.4.2. CJP joints carry the full design strength of the base metal. PJP joints carry a reduced effective throat, and the engineer must account for this in the design.
A CJP weld is indicated on a welding symbol by showing the groove type (V, bevel, J, U, or square) without a depth dimension in the weld size position. When no depth dimension appears, the weld is understood to be CJP. If a depth dimension is shown, the weld is PJP to that depth. Additional information such as groove angle, root opening, and backing requirements appear in their standard positions on the symbol. A tail note may specify the WPS number or welding process.
Yes. D1.1:2025 Clause 5.4.1 defines prequalified CJP groove weld details. The joint configuration must match one of the prequalified details in Figure 5.1, including the specified groove type, root opening, groove angle, and root face dimensions. The welding process must be SMAW, SAW, GMAW (except short-circuit transfer), or FCAW. The base metal must be listed in Table 5.6, and all other Clause 5 provisions must be met. Prequalified CJP joints do not require a PQR or qualification testing under Clause 6.