Welding quality cannot be verified only by looking at the completed product. Effective control begins with the drawing and continues through material preparation, procedure selection, fabrication, inspection and final documentation.
Because welding is influenced by many variables, buyers and manufacturers should agree on the applicable quality requirements before production begins.
Quality Starts with Contract and Drawing Review
Before welding, the manufacturer should review the technical information supplied by the buyer. Important inputs include:
- Base material and thickness;
- Joint type and preparation;
- Weld size, length and location;
- Welding symbols;
- Service conditions;
- Dimensional and distortion limits;
- Applicable welding standard;
- Inspection and acceptance requirements.
Ambiguous weld symbols or missing acceptance criteria should be clarified before fabrication. ISO 2553 provides a recognized framework for representing welded joints on drawings, although the specific standard and symbol system must be confirmed for each project. ISO 2553:2019
The review should also determine whether the specified joint is accessible for welding and inspection. A theoretically correct design may still create production difficulties if the torch, welding gun or inspection equipment cannot reach the required area.
Material Identification and Preparation
Weld quality depends partly on using the correct base and filler materials. Material grade, thickness and condition influence joint preparation, welding parameters, heat input and potential preheating requirements.
Before welding, production controls may include:
- Confirming material identity;
- Checking surfaces for rust, oil, paint and contamination;
- Preparing the specified bevel or joint geometry;
- Verifying joint gap and alignment;
- Controlling the condition of filler materials;
- Separating materials where cross-contamination is a concern.
Where traceability is contractually required, identification must be maintained from the incoming material through cutting and fabrication.
Welding Procedures and Essential Variables
A welding procedure provides instructions for producing a weld under defined conditions. Depending on the applicable standard and contract, this may involve a Welding Procedure Specification and supporting procedure qualification records.
Variables can include the welding process, base material group, filler metal, current, voltage, travel speed, welding position, preheat and interpass temperature.
ISO 15614-1 covers welding procedure tests for arc and gas welding of steels and arc welding of nickel and nickel alloys. Its applicability depends on the material, process, product and contractual requirements. ISO 15614-1:2017
ISO 3834 provides a broader framework for selecting quality requirements for fusion welding. It recognizes that welding quality must be built into the process, rather than relying solely on inspection after fabrication. ISO 3834-1:2021
A buyer should not assume that every project automatically requires qualification to a particular code. The applicable procedure, qualification basis and documentation should be stated in the RFQ or purchase order.
Welder Competence and Production Control
Even a suitable procedure depends on competent personnel and controlled execution. The required qualification of welders should be determined by the governing standard and project specification.
During production, controls may cover:
- Fit-up before welding;
- Welding sequence;
- Tack weld condition;
- Preheat and interpass temperature;
- Cleaning between passes;
- Heat input where applicable;
- Prevention of arc strikes and surface damage;
- Control of distortion;
- Identification of completed welds.
For large fabricated assemblies, welding sequence and fixturing can be important because heat causes local expansion and contraction. If distortion is not considered, the completed assembly may fail dimensional requirements even when the weld itself appears acceptable.
Visual Inspection
Visual inspection is normally one of the first and most widely used weld examination methods. It may be carried out before, during and after welding.
Checks can include joint preparation, alignment, weld size, profile, surface condition and visible imperfections. ISO 17637 addresses visual testing of fusion-welded joints and remains current following its latest confirmation. ISO 17637:2016
Visual inspection does not identify every type of internal or subsurface imperfection. It should therefore be used within an inspection plan based on product risk, contractual requirements and the applicable fabrication standard.
When Is NDT Required?
Additional NDT may be specified where visual inspection alone is insufficient. Common methods include:
- Penetrant testing for surface-breaking discontinuities;
- Magnetic particle testing for surface and near-surface discontinuities in suitable ferromagnetic materials;
- Ultrasonic testing for certain internal discontinuities;
- Radiographic testing to produce an image of internal weld conditions.
The correct method depends on material, joint geometry, thickness and the type of imperfection being investigated. The RFQ should specify examination coverage, acceptance criteria and reporting requirements.
Where certified personnel are required, ISO 9712 defines qualification and certification requirements for industrial NDT personnel across several methods. ISO 9712:2021
Nonconformity and Repair
If a weld does not meet the agreed criteria, the nonconformity should be recorded and evaluated. The response may involve acceptance under an approved concession, repair under an authorized method or rejection and remanufacture.
A repaired weld may require renewed inspection. Repair should not be treated as informal grinding and rewelding without technical review.
Applying Project-Specific Welding Control at TOMECO SI
TOMECO SI manufactures custom metal components and mechanical assemblies to customer drawings and specifications. Welding, dimensional checks and agreed inspection activities are planned according to the product and contractual requirements.
Buyers should identify the applicable welding code, acceptance criteria, inspection scope and required records at the RFQ stage. This allows the required controls to be evaluated and agreed before production.
