The difference between welding process evaluation and welding process regulations

Welding process evaluation (WPQ) and welding process regulations (WPS) are two core links in the welding quality control system, and they together constitute the technical foundation of modern welding projects. The former uses systematic tests to verify the feasibility of the welding process, while the latter uses the operation specifications that convert the verification results into repeatable operation. The two work together to ensure that the performance of the welds meets the design requirements and together form the quality cornerstone of modern welding projects.

• Differences between definition and core
  1. ​Welding Process Assessment (WPQ)​

Welding process evaluation is to verify the feasibility and reliability of the welding process through tests, ensure that the weld performance meets the standard requirements (such as strength, toughness, etc.), generate the "Procedure Qualification Record" (PQR, Procedure Qualification Record), and record the test data and results. The core goal is to establish a reliable welding performance guarantee system. For example, in the manufacturing of nuclear power equipment, the mechanical properties of the joint need to be verified through tensile, bending, impact tests (such as low-temperature impact of -40℃). According to ASME IX standards, steel plates with thicknesses exceeding 50mm also require Z-direction tensile tests to assess the risk of layered tear.

1. 2. ​Welding Process Procedure (WPS)​

The operation guidance documents for guiding production based on qualified PQRs specify detailed technical requirements such as welding methods, materials, parameters, preheating temperature, etc., and provide specific operation guidance for welders or operators to ensure production consistency. As an operation guidance document, WPS needs to clarify the tolerance range of welding parameters. For example, the current fluctuation of gas protective welding (GMAW) must be controlled within ±5%, and the bevel angle must be marked as 60±5°. The regulations need to consider actual variables such as equipment model differences (such as arc characteristics of different welding machines), environmental conditions (such as marine engineering requires simulation of cathode protection environment).

1. 3. Logical relationships
      1. Assessment first and then procedure:

The WPQ test must be completed and a PQR is generated before WPS can be formulated based on the PQR.

1. 1. 2. One-to-many possibilities:

A qualified PQR may derive multiple WPS (for example, adjusting secondary parameters).

1. 1. 3. Irreversibility:

The parameters of WPS must be within the range verified by PQR, and if they exceed them, they must be re-evaluated.

• Comparative analysis of technical elements
  1. Core elements of welding process evaluation

Test items: including mechanical properties tests such as tensile, bending, and impact;

Recording requirements: Key parameters such as preheating temperature, interlayer temperature, and heat input must be fully recorded;

Validity period: usually 3 years, but depending on the frequency of standard updates;

Change rules: Changes in material groups, thickness ranges, and welding position need to be reassessed;

1. 2. Technical requirements for welding process regulations

Parameter range: The tolerance bands of current, voltage and speed must be clearly defined;

Operational guidelines: including welding bead arrangement, root cleaning method, post-heat measures, etc.;

Version control: a file revision record and version traceability mechanism are required;

Applicability: Applicable material thickness, pipe diameter range and other restrictions must be marked

• Quality control and innovative development
  1. Digital monitoring system

The Internet of Things technology is used to collect welding parameters (such as arc voltage, gas flow) in real time, and abnormal data automatically triggers an alarm. After the implementation of a shipyard, the weld repair rate dropped from 2.3% to 0.4%.

1. 2. International mutual recognition mechanism

Reduce repeated trials by combining assessments (such as ISO 15614-1 and ASME IX linkage). A pressure vessel company uses orthogonal test matrix to optimize parameters, and the test cost is reduced by 38%.

• Economic and safety management

Strictly implementing the WPQ/WPS system can significantly reduce costs. Statistics from a certain engineering machinery manufacturer show that the proportion of unqualified welds has been reduced through standardized processes, the overall manufacturing cost has been reduced by about 20%, the single-piece welding labor time has been reduced by 25%, and the production efficiency has been improved by 15%. In addition, good welding quality management has enhanced the market competitiveness of the products and won the trust of more customers.

Conclusion​: From laboratory verification to on-site operation, WPQ and WPS form a complete closed-loop of quality. With the development of technologies such as robot welding and digital twins, the two are evolving from single process control to intelligent manufacturing integration, and continue to promote technological innovation in welding projects.