Weld Map Documentation: ISO 3834 & ASME B31.3 Compliance

Weld map documentation is the cornerstone of traceable fabrication — and the first document an auditor requests when verifying compliance with ISO 3834, ASME B31.3, or EN 1090. Yet in most fabrication shops it is assembled retrospectively, from scattered paper records, days before the surveillance visit. That approach fails — and it fails predictably.

This guide explains what a weld map must contain, how ISO 3834, ASME B31.3, and EN 1090-2 frame their documentation requirements, how to build a numbering system that scales, the most common audit failures, and how digital weld map platforms change the equation.

Key Takeaways

• A weld map assigns a unique identifier to every weld joint and links it to the applicable WPS, welder, NDT results, and inspection status.
• ISO 3834-2 Clause 7 mandates weld-level traceability; a weld map is the standard method of satisfying it for complex fabrications.
• ASME B31.3 requires each weld to be traceable by number to the welder ID, WPS, PWHT records, and examination results.
• EN 1090-2 EXC3/EXC4 demands the most detailed weld map data; EXC2 requires a streamlined subset.
• The three most common audit failures are: missing welder ID for repaired welds, NDT status not updated after re-inspection, and weld IDs that reference a WPS revision that does not match the as-welded date.
• Digital weld maps eliminate transcription gaps and enable real-time audit dashboards, but the data model must be defined before fabrication begins — not after.

Table of Contents

• What Is a Weld Map?
• Core Data Fields for Every Weld ID
• ISO 3834 Documentation Requirements
• ASME B31.3 Weld Traceability Requirements
• EN 1090-2 Execution Class Requirements
• How to Create a Weld Map: Step-by-Step
• Common Failure Modes and How to Fix Them
• Paper vs Digital Weld Maps
• Frequently Asked Questions

What Is a Weld Map?

A weld map is a dimensioned drawing — or a marked-up engineering drawing — on which every weld joint in a fabricated assembly is identified by a unique alphanumeric identifier. The identifier, commonly called a weld number or weld ID, links the physical joint to a set of associated records: the Welding Procedure Specification (WPS), the qualified welder who performed the weld, the pre- and post-weld inspections, NDT results, and any repair history.

For piping systems, the weld map is typically created on isometric drawings (ISO drawings), with each weld numbered along the pipe route. For structural steel, weld numbers are marked on general arrangement drawings or 3D model exports. Pressure vessels and heat exchangers use dedicated fabrication drawings with weld seam designations per ASME Section VIII or EN 13445.

The weld map is not a standalone document: it is the index key that makes every other quality record findable during an audit. Without it, a quality dossier is a pile of disconnected papers.

Core Data Fields for Every Weld ID

The minimum set of fields varies by standard, but the following table represents the common denominator for ISO 3834-2 / ASME B31.3 / EN 1090-2 EXC3 compliance:

ISO 3834 Documentation Requirements

ISO 3834 is a family of five parts that defines quality requirements for fusion welding of metallic materials. Part 2 (comprehensive) and Part 3 (standard) are the most commonly specified in industrial contracts and third-party certification schemes. For a practical audit checklist, see our ISO 3834 & EN 1090 audit guide.

ISO 3834-2 Clause 7 — Welding documentation requires the manufacturer to prepare, maintain, and make available:

• A list of applicable WPS for each joint category in the fabrication.
• Evidence that each welder or welding operator performing the work holds a valid qualification for the process, material group, and thickness range used.
• Records linking each production weld to its applicable WPS, responsible welder, and inspection results.
• A non-conformance and repair record for any weld that failed first-off inspection, documenting the repair WPS used and the result of re-inspection.

The weld map is the practical tool for meeting the third requirement. Without a spatial identifier (weld number on a drawing), the link between the physical joint and the paper trail cannot be established unambiguously.

For subcontractors supplying weld maps to prime contractors or Notified Bodies, TWI recommends that the weld map format is agreed before fabrication begins — not after the first audit finding.

ASME B31.3 Weld Traceability Requirements

ASME B31.3 Process Piping governs the design and fabrication of chemical plant and petroleum refinery piping. Paragraph 328.4 (Records) requires:

• Each weld number to be recorded in a traveller or equivalent document, traceable to the welder ID, WPS number, and date.
• For systems in Fluid Category D and Normal Fluid Service, progressive examination records are required per Para. 341.3.
• For severe cyclic conditions or High Pressure (Chapter IX), a complete examination matrix referencing each weld by number is mandatory.
• PWHT records (Para. 331.2) must reference the specific weld numbers heat-treated, the temperature profile, heating/cooling rates, and hold time.

In practice, most ASME B31.3 projects implement weld maps on isometric drawing packages marked up by the fabricator’s QC team. Each weld is assigned a sequential number on the ISO drawing (e.g. W-001 through W-142 for a given spool), and the QC dossier is indexed against those numbers.

For high-pressure and Category M fluid service, the ASME B31.3 documentation package becomes legally binding — inadequate weld maps can delay hydrotest sign-off or final acceptance by the Authorized Inspector.

EN 1090-2 Execution Class Requirements

EN 1090-2 specifies technical requirements for the execution of structural steel components. The documentation requirements scale with the Execution Class (EXC):

For EXC3 and EXC4 bridges, pressure vessels, crane runway beams, and lifting equipment, the weld map is submitted to the Notified Body as part of the Factory Production Control (FPC) documentation required under the Construction Products Regulation (CPR). For a full breakdown of EN 1090-2 execution class requirements, see our EN 1090-2 structural welding guide.

A recurring finding in EN 1090 surveillance audits is the misclassification of execution class: the building specification assigns EXC2, but the structural engineer’s notes indicate EXC3 requirements for specific connections. Weld maps must reflect the highest class applicable to each joint, not the overall project class.

How to Create a Weld Map: Step-by-Step

Step 1 — Obtain the Release-for-Construction Drawing Set

Weld maps must be based on approved-for-construction (AFC) drawings. Using preliminary drawings risks numbering welds that are later modified or deleted. Confirm the drawing revision on the weld map header matches the AFC revision.

Step 2 — Define the Weld Numbering Convention

Establish a systematic numbering scheme before marking up drawings. A consistent system eliminates duplicate IDs and makes the audit trail self-explanatory. Example conventions:

• Piping: [Area]-[ISO No.]-[Joint Type]-[Sequence] → P1-025-BW-007
• Structural: [Frame]-[Node]-[Seam] → F3-N12-S2
• Pressure vessel: [Shell/Head Code]-[Seam Type]-[Sequence] → SH-L-003 (longitudinal seam 3 on shell)

Document the numbering convention in a Weld Map Procedure (a short internal document, 1-2 pages) referenced in your quality plan.

Step 3 — Mark Up the Drawing

Annotate each weld joint on the drawing with its unique ID. For piping isometrics, mark the weld symbol plus the number in a balloon. For structural drawings, use a numbered bubble at each weld location.

At the same time, create a corresponding Weld Data Sheet or Weld Log — a tabular spreadsheet or database record with one row per weld ID, containing all the fields listed in the core data table above.

Step 4 — Link WPS Before Welding Begins

Before any production welding starts, the responsible Welding Coordinator (per ISO 14731) must assign the applicable WPS to each weld ID in the log. This prevents the common failure mode of a welder selecting a WPS at the machine that does not cover the material thickness, position, or process required.

Step 5 — Record Welder Stamp at Completion

The welder stamps or initials the joint identifier on the as-built drawing (or marks the log) immediately after completing the weld. This is the chain-of-custody moment — if it is missed, reconstructing the welder identity later is unreliable.

Step 6 — Update NDT Status in Real Time

As each weld is tested, the result (Pass / Fail / Repair) is entered against the weld ID in the log, referencing the NDT report number. The weld map drawing is updated with a status code (e.g. green = pass, red = fail pending repair, blue = repair accepted).

Step 7 — Close Out the Dossier

Before sign-off, verify that every weld ID on the drawing has:

• A WPS reference ✓
• A welder ID ✓
• A visual inspection sign-off date ✓
• An NDT result (where required) ✓
• No open repair actions ✓

Tools such as the Therness HeatCore QMS integrate weld map close-out checklists directly into the digital record, flagging incomplete rows before the dossier is submitted.

Common Failure Modes and How to Fix Them

Failure 1: Missing Welder ID on Repaired Welds

Repair welds are frequently stamped by a different welder than the original. The weld log records the original welder but not the repair welder — or records the repair welder and overwrites the original.

Fix: Add a dedicated Repair Welder ID column in the log. The original welder ID stays; the repair welder ID and repair WPS are recorded in separate columns.

Failure 2: NDT Status Frozen at “Pending”

When a weld fails first-off NDT and is repaired, the repair is recorded in a separate NDT report. The weld log is updated with “repair complete” but the original NDT report number stays — auditors cannot find the follow-up report without a cross-reference field.

Fix: Add a Follow-up NDT Report field in the log, populated with the report number of the re-inspection after every repair.

Failure 3: WPS Revision Mismatch

A WPS revision is issued mid-project (e.g., to add a new material thickness or filler metal brand). Welds made before the revision reference the old revision; welds after reference the new one. Without explicit revision tracking in the weld log, auditors cannot confirm which welds were covered by which revision.

Fix: Record the WPS revision (not just the document number) in the weld log, and index WPS change dates against the welding date column. Any weld made between a WPS revision date and the next revision date must reference the revision in force at that time.

Failure 4: Paper Weld Maps Lost or Illegible

Paper isometrics stamped by welders on the shop floor are handled repeatedly. After months of fabrication, the stamps are smudged, the paper is torn, and the pencil annotations are illegible. A third-party NDT sub-contractor issues reports using their own weld numbering convention, which does not match the fabricator’s.

Fix: Require sub-contractors to use your weld numbering scheme by contract. Digitise paper weld maps as a controlled QMS record immediately after each inspection, not at project closeout.

Paper vs Digital Weld Maps

Digital weld map systems embedded in QMS platforms — including solutions that integrate with Therness real-time weld monitoring — link each weld ID to live production data: arc time, heat input, interpass temperature, and camera footage. This creates an audit trail that goes beyond documentation and into process evidence, which is increasingly requested by tier-1 OEMs and notified bodies for EXC3/EXC4 and nuclear applications.

Research by TWI indicates that digital weld data management reduces non-conformance rates by 20-35% in complex fabrication environments, primarily by catching missing data fields in real time rather than at final inspection.

For projects subject to ASME NQA-1 (nuclear quality assurance) or ISO 19443 (nuclear supply chain), digital records are the only practical means of satisfying 10-CFR-50 Appendix B documentation requirements across hundreds of weld joints.

Frequently Asked Questions

What is a weld map in welding fabrication?

A weld map is a dimensioned drawing or diagram of a fabricated structure on which every weld joint is assigned a unique identifier (e.g. W-001). Each ID links to the applicable WPS, welder qualification, NDT requirements, and inspection results, creating a complete audit trail for each joint.

Is a weld map required by ISO 3834?

ISO 3834-2 Clause 7 requires that welding documentation identifies each weld with its applicable WPS and responsible welder. A weld map is the standard method for meeting this requirement in complex fabrications. ISO 3834-3 (standard quality level) has reduced but still present traceability obligations.

Does ASME B31.3 require weld maps?

ASME B31.3 (Process Piping) requires that each weld be identified by a unique weld number traceable to the welder ID, WPS, heat treatment records, and examination results. Most EPC contractors implement this as a physical weld map on isometric drawings or P&IDs marked up with weld numbers.

What fields must a weld map contain for EN 1090-2 compliance?

For EN 1090-2 Execution Class EXC3 or EXC4, the weld map must record: weld joint ID, joint type and geometry, applicable WPS reference, welder ID and qualification standard, NDT method and acceptance class, inspection status, and any repair records. EXC2 requires a subset of these fields.

What is the difference between a weld map and a weld log?

A weld map is a graphical document — typically an annotated drawing — that shows the location of every weld on the structure. A weld log (or weld traveller) is a tabular record that captures the data fields for each weld ID. The two documents complement each other: the map provides spatial context, the log provides detailed traceability data.

How do you assign weld numbers in a weld map?

The most common system uses a prefix indicating the joint type (BW for butt weld, FW for fillet weld, SW for socket weld) followed by a sequential number and optionally a spool or assembly prefix. For piping: P-ISO-001-BW-003 = third butt weld on isometric 001. For structures: the weld number often references the member or node it connects.

Can a weld map be digital?

Yes. Digital weld maps embedded in CAD files, IFC models, or dedicated QMS platforms link weld IDs to live data records — WPS PDFs, welder certificates, NDT reports, inspection sign-offs. Digital formats reduce transcription errors, enable real-time audit dashboards, and are increasingly required by major EPC contractors and Notified Bodies. Learn more about Therness digital welding traceability.

What happens during an audit if your weld map is incomplete?

An incomplete weld map is a Major non-conformance under ISO 3834-2 and a Conditional Hold in ASME PED inspections. The auditor will issue a Corrective Action Request (CAR) requiring you to reconstruct the missing records — often from memory or secondary sources — before the next audit stage. If records cannot be reconstructed, the affected welds may require re-testing or rejection.