Why is it necessary to formulate welding procedure specifications before welding?

A Welding Procedure Specification (WPS) is a standardized guideline document for welding operations. Its development is a critical step in ensuring welding quality, safety, and consistency. The following are the main reasons and detailed analysis for developing a WPS before welding:

1. Ensuring Welding Quality and Performance

Material Compatibility: Different base materials (such as carbon steel, stainless steel, and aluminum alloys) have specific requirements for welding parameters (current, voltage, preheat temperature, etc.). The WPS clearly defines the appropriate welding materials and processes to avoid defects such as cracks and porosity caused by inappropriate parameters.

Mechanical Performance Assurance: The feasibility of the procedure is verified through a process qualification (PQR) to ensure that weld strength, toughness, and other indicators meet design standards (such as ASME and ISO 15614).

Adaptability to Special Working Conditions: For example, welding in low-temperature or high-pressure environments requires preheating and interpass temperature control measures to prevent brittle fracture.

2. Standardization and Repeatability

Unified Operating Procedures: The WPS clearly defines details such as welder technique (such as electrode angle and travel speed) and equipment settings, minimizing human variability and ensuring consistency across batch production. Traceability and Responsibility Allocation: Regulations serve as technical documents, providing a traceability basis for quality incidents and clarifying process responsibilities.
3. Safety and Compliance Requirements
Hazard Prevention and Control: For example, high-strength steel welding requires controlling hydrogen content to prevent cold cracking. Regulations specify the use and drying requirements of low-hydrogen electrodes.
Regulatory Compliance: Industry standards (such as AWS D1.1 and EN 1090) mandate WPS, especially for critical structures such as pressure-bearing equipment and bridges. Welding that fails to pass the process qualification is considered non-compliant.
4. Cost and Efficiency Optimization
Reducing Rework: Pre-testing to determine optimal parameters avoids material waste and project delays caused by on-site commissioning.
Resource Allocation: Regulations clearly specify the need for auxiliary measures (such as back shielding gas), allowing for pre-planning of resources and improving efficiency.
5. Precise Control of Special Processes
Automated Welding: Robotic welding relies on precise programming parameters, and regulations serve as the foundation for code input.
Dissimilar Metal Welding: For example, welding copper to steel requires a specific transition layer. Regulations specify material selection and overlay sequence.
Supplementary Note: The core content of procedure development usually includes:

Types and specifications of base metal and welding consumables;

Groove design and cleaning requirements;

Welding method (SMAW, TIG, etc.) and parameters;

Preheat/postheat temperatures and heat treatment processes;

Inspection methods (RT, UT, etc.) and acceptance criteria.

In summary: The welding procedure specification is the "technical constitution" of welding projects. Through scientific and standardized methods, it mitigates risks at the source and ensures structural reliability and economic efficiency. Ignoring procedure development can lead to catastrophic consequences, such as the 2018 pipeline explosion at a chemical plant caused by welding not following procedures.