Interview Questions for BS EN ISO 128-20

BS EN ISO 128-20, or simply ISO 128-20, is a crucial international standard specifying the requirements for welder qualification, testing, and certification. Its scope encompasses various welding processes and materials used in the construction and manufacturing industries. Essentially, it ensures the consistent quality and safety of welded joints by standardizing how welders are qualified and how welding procedures are defined and controlled. It applies to various sectors needing reliable welding, from shipbuilding and pressure vessel fabrication to pipeline construction and automotive manufacturing.

Think of it as the ‘driver’s license’ for welders. Just as a driver’s license assures road safety, ISO 128-20 ensures the safety and reliability of welded structures.

ISO 128-20 covers a wide range of welding processes. The specific processes covered depend on the specific national adaptation or addendum to the standard, but generally, it includes processes like:

• Gas metal arc welding (GMAW): Also known as MIG welding, it uses a consumable electrode and a shielding gas.
• Gas tungsten arc welding (GTAW): Also known as TIG welding, it uses a non-consumable tungsten electrode and a shielding gas.
• Shielded metal arc welding (SMAW): Also known as stick welding, it uses a consumable electrode coated with flux.
• Submerged arc welding (SAW): A high-deposition rate process where the arc is submerged in a granular flux.
• Flux-cored arc welding (FCAW): Uses a tubular electrode containing a flux core.
• Resistance welding (spot, seam, projection): Using electrical resistance to generate heat at the weld joint.

The standard doesn’t dictate which processes must be covered but provides a framework for qualifying welders in any process used.

Welder qualification according to ISO 128-20 involves demonstrating competency through both a practical test (performing a weld) and a visual examination of the resulting weld. The specific requirements depend on the welding process and the materials being welded. The process typically involves these steps:

• Selection of test pieces: Specific dimensions and materials are chosen based on the intended application.
• Welding procedure specification (WPS): A detailed document outlining all parameters for the weld test.
• Practical test: The welder produces test welds according to the WPS.
• Visual inspection: Trained inspectors examine the welds for surface defects.
• Destructive testing (optional): Tests such as tensile, bend, and impact tests might be required depending on the application’s criticality.
• Certification: Upon successful completion, the welder receives a certificate of competence valid for a specific period and welding processes.

Imagine it like a driving test: You must demonstrate your ability to handle the vehicle safely and correctly. Similarly, welders need to show their skills in creating sound, safe welds.

Controlling essential variables during welding is crucial for ensuring consistent weld quality and meeting the required standards. These variables, detailed within the WPS, influence the weld’s mechanical properties and appearance. Key variables include:

• Welding current and voltage: These directly affect the heat input.
• Welding speed: Affects the heat input and weld bead geometry.
• Electrode type and diameter: Affects the weld metal composition and properties.
• Shielding gas type and flow rate: Prevents atmospheric contamination.
• Preheating and post-weld heat treatment: Improves weld properties and reduces cracking.
• Joint design and preparation: Influences weld strength and appearance.
• Base material properties: The material’s chemical composition and mechanical properties.

Think of it as a recipe for a cake: If you don’t control the ingredients (variables) precisely, you won’t get the desired result.

Interpreting a WPS requires a thorough understanding of welding parameters and the standard. A WPS is a detailed document that outlines all the essential variables for a specific welding procedure, ensuring repeatability and consistency. A well-written WPS will include:

• Process identification: (e.g., GMAW, SMAW)
• Base material specification: (Grade, thickness)
• Joint design and preparation: (Type of joint, root opening, bevel angle)
• Welding parameters: (Current, voltage, speed, wire feed speed, gas flow rate)
• Pre-heat and interpass temperature: (If required)
• Post-weld heat treatment: (If required)
• Weld quality requirements: (Visual inspection criteria, other tests)

Imagine it as a detailed blueprint for a welder, ensuring that each weld is produced to the same exacting standards.

Welder performance qualification records are essential for demonstrating compliance with ISO 128-20 and ensuring the quality of welded structures. These records provide traceable evidence that the welder has been successfully qualified according to the specified procedures. They are critical for:

• Audits and inspections: Demonstrating compliance with quality management systems.
• Legal requirements: Meeting regulatory requirements for safety and quality.
• Traceability: Identifying welders who performed specific welds in a structure.
• Continuous improvement: Analyzing performance data to improve welding procedures.

Think of them as a passport for a welder – they confirm their credentials and capabilities.

Welding defects can significantly compromise the integrity and safety of a welded joint. These defects can originate from various causes related to the welding process or the base material. Common types include:

• Porosity: Gas pockets within the weld metal, often caused by improper shielding gas coverage or contamination.
• Cracks: Breaks in the weld metal, typically caused by high stresses during cooling or hydrogen embrittlement.
• Incomplete penetration: The weld doesn’t fully fuse the base materials, potentially weakening the joint. Poor joint design or insufficient welding parameters are often to blame.
• Undercut: A groove melted into the base material at the edge of the weld, resulting in reduced strength and poor appearance. Usually caused by excessive welding current or improper travel speed.
• Slag inclusion: Trapped slag from the welding process within the weld metal, leading to reduced strength and ductility. Inadequate cleaning between weld passes is a common cause.
• Lack of fusion: The weld metal does not properly fuse with the base metal. This can arise from poor joint preparation or insufficient heat input.

Understanding the causes of these defects is essential for implementing corrective actions and preventing their occurrence in future welds.

Inspecting welds for defects involves a multifaceted approach, combining visual examination with advanced non-destructive testing (NDT) methods. Visual inspection is the first step, checking for obvious flaws like cracks, porosity, or lack of fusion. However, many defects are internal and invisible to the naked eye, requiring more sophisticated techniques.

• Visual Inspection: This involves carefully examining the weld for surface imperfections using appropriate lighting and magnification tools. It’s a crucial first step, often revealing serious issues requiring immediate attention.
• Non-Destructive Testing (NDT): This comprises various methods like radiography, ultrasonic testing, magnetic particle inspection, and liquid penetrant testing, each capable of detecting different types of defects at various depths within the weld.

Imagine searching for a hidden flaw in a cake: a visual check might reveal a burn on the surface, but X-ray (radiography) is needed to see any internal cavities.

Non-destructive testing (NDT) plays a pivotal role in ensuring weld quality by providing a detailed assessment of the weld’s internal structure and integrity without causing damage. It helps identify potential flaws that might compromise the structural soundness or longevity of the welded joint. This prevents costly rework, failures in service, and potential safety hazards. NDT methods help achieve a high level of confidence in the structural integrity of the welded component.

For instance, in a bridge construction, NDT ensures that the welds holding massive steel beams together are free from critical defects, ensuring the safety of thousands of vehicles daily. Failure to detect these flaws could have catastrophic consequences.

BS EN ISO 128-20 doesn’t prescribe specific NDT methods, but it acknowledges the use of various techniques depending on the application and material. The choice of method depends on factors like weld access, material thickness, and the type of defects expected.

• Radiographic Testing (RT): Uses X-rays or gamma rays to reveal internal flaws like porosity, cracks, and inclusions.
• Ultrasonic Testing (UT): Employs high-frequency sound waves to detect internal flaws and measure weld thickness. It’s particularly effective for detecting planar defects.
• Magnetic Particle Testing (MT): Suitable for ferromagnetic materials, this method detects surface and near-surface cracks by magnetizing the weld and applying magnetic particles.
• Liquid Penetrant Testing (PT): Detects surface-breaking defects in any material by applying a penetrant that seeps into the cracks and is then revealed by a developer.
• Visual Testing (VT): A simple but essential initial inspection to detect obvious surface defects.

Interpreting radiographic images requires trained personnel. Radiographers look for variations in density (darker or lighter areas) that indicate discontinuities in the weld. These variations can correspond to different types of defects. A dark area might represent a void (porosity) or lack of fusion, while a lighter area might suggest an inclusion or reinforcement. The size, shape, and location of these indications are crucial factors in determining the weld’s acceptability. Reference standards are used for comparison and to categorize the severity of the detected flaws.

Think of it like reading a medical X-ray: a trained professional interprets the image’s nuances to identify potential problems. The experience of the interpreter is vital for correct identification and assessment of weld integrity.

BS EN ISO 128-20 doesn’t specify single acceptance criteria; instead, it provides a framework. Acceptance criteria are determined based on the application, the design requirements, the relevant codes and standards, and the level of risk. The specific criteria should be defined in the relevant welding procedure specification (WPS) and the contract documents. These criteria might include limits on the size, type, and number of allowable defects. Exceeding these limits may necessitate repair or rejection of the weld. The interpretation of these criteria and decision making are often reliant on skilled personnel and their experience.

A key aspect is the distinction between critical and non-critical defects: a small porosity might be acceptable in some applications while a large crack would be deemed unacceptable.

Developing a Welding Procedure Qualification Record (WPQR) is a crucial step in ensuring consistent weld quality. It involves performing a series of test welds according to a specific welding procedure specification (WPS). These test welds are then subjected to thorough inspection, including visual inspection and appropriate NDT methods as dictated by the relevant standards (for example, ISO 15614-1 for testing of welds).

• Procedure Development: Define all welding parameters – base material, filler material, pre-heat temperature, welding process, etc.
• Test Weld Production: Perform several test welds according to the WPS, ensuring strict adherence to the parameters.
• Testing and Inspection: Conduct NDT and other required testing (mechanical testing may also be required depending on the intended application). This process can often include macroscopic and microscopic examination.
• Documentation: Meticulously document all parameters, test results, and inspection findings. This forms the WPQR.

Think of a WPQR as a recipe for making a perfectly consistent weld. Following it ensures reproducible results and quality control. Any deviation requires a new WPQR to be generated and approved.

A Welding Procedure Specification (WPS) and a Welding Procedure Qualification Record (WPQR) are closely related but serve different purposes:

• WPS: A document outlining the detailed parameters for performing a specific weld. It acts as a set of instructions for the welder. It references the applicable WPQR that proves the procedure is capable of producing acceptable welds.
• WPQR: A record of the tests performed to prove that the WPS can consistently produce welds meeting the required standards. It documents the results of those tests. It serves as proof of the welding procedure’s validity.

The WPS tells *how* to make the weld; the WPQR proves that the method in the WPS produces acceptable welds. Imagine a cake recipe (WPS) and a successful cake made according to that recipe (WPQR) – both are needed to produce a consistent result.

The Welding Coordinator is a crucial role in ensuring compliance with BS EN ISO 128-20. Think of them as the orchestra conductor for a welding project. They are responsible for the overall welding management system, ensuring all activities are planned, controlled, and documented correctly. This includes selecting qualified welders, approving welding procedures, overseeing welder performance, managing non-conformances, and maintaining records. They are the central point of contact for all welding-related matters and act as a liaison between the welding team, the client, and other relevant parties. In essence, they guarantee the quality and safety of the welding work.

For example, in a large-scale construction project involving diverse welding processes, the Welding Coordinator ensures all welders use approved procedures, materials are correctly identified and traced, and any deviations are dealt with promptly and documented. They might oversee welder qualifications, schedule welding inspections, and ensure adherence to all relevant safety regulations.

ISO 128-20 mandates a robust system for managing welding procedures. It emphasizes the importance of creating, qualifying, and controlling these procedures to ensure consistent, high-quality welds. The standard details the requirements for procedure qualification records (PQRs) and welding procedure specifications (WPSs). PQRs are detailed records documenting the parameters used during the qualification tests, while WPSs outline the parameters to be used for production welds based on the successful PQR. Imagine a recipe for welding: the PQR is like rigorously testing a recipe to ensure it produces a delicious cake (a qualified weld), and the WPS is the recipe you then use for consistent baking (welding).

The standard also dictates the process for updating and revising these procedures should changes occur, such as using different materials or equipment. This control ensures traceability and prevents potential inconsistencies in the welding processes, contributing to overall project quality and safety.

Handling non-conformances, essentially any deviation from the approved WPS or other relevant standards, is critical. ISO 128-20 requires a documented system for identifying, investigating, and rectifying these issues. This typically involves a structured process of:

• Identification: A visual inspection, testing, or other assessment reveals a flaw.
• Investigation: Determining the root cause of the non-conformity. This may involve analyzing the welding procedure, welder performance, or materials used.
• Corrective Action: This might involve re-welding, repairing the defect, or revising the welding procedure to prevent recurrence.
• Documentation: Meticulously recording all details of the non-conformity, investigation, and corrective actions taken. This is crucial for traceability and continuous improvement.

For example, if a weld shows signs of porosity (small holes), a thorough investigation might reveal incorrect shielding gas usage. The corrective action would be to re-weld the joint with the correct gas, and the procedure might be updated to emphasize the importance of gas purity checks.

Traceability in welding is paramount for ensuring accountability and quality. It’s like leaving a breadcrumb trail to track every step of the process. ISO 128-20 mandates traceability to ensure that every weld can be linked back to its WPS, PQR, welder qualifications, materials used, and inspection records. This enables easy identification of the source of any defects, facilitating efficient corrective actions and ultimately preventing future issues.

A real-world example: Imagine a bridge weld fails. Traceability allows engineers to quickly identify the specific weld, the welder who made it, the materials used, and the procedure followed. This information is vital for determining the root cause of the failure and avoiding similar incidents in the future. It also assists with legal and insurance claims.

Quality control plays a central role in ensuring compliance with ISO 128-20. It’s the ongoing process of monitoring and verifying that welding processes and products meet the specified requirements. This includes:

• Pre-weld checks: Verifying materials, equipment, and welder qualifications before welding begins.
• In-process checks: Monitoring the welding process itself, such as observing the welding parameters and ensuring adherence to the WPS.
• Post-weld inspections: Conducting thorough inspections of the welds to detect defects using visual inspection, non-destructive testing (NDT) methods like radiography or ultrasonic testing, or destructive testing.
• Audits: Regular audits of the welding management system to identify potential weaknesses and ensure continual improvement.

Quality control acts as a continuous feedback loop, allowing for timely detection and correction of any discrepancies, ensuring consistently high quality welds throughout the project.

There’s a variety of weld joints, each suitable for different applications. Here are a few examples:

• Butt Joint: Two pieces of metal are joined end-to-end, creating a continuous surface. Used extensively in pipelines and structural steel fabrication.
• Lap Joint: One piece overlaps another. Simpler to weld than a butt joint but less strong. Often found in sheet metal work.
• T-Joint: One piece is perpendicular to another. Common in structural applications where beams are joined to columns.
• Corner Joint: Two pieces are joined at a 90-degree angle. Frequently used in box-section structures.
• Edge Joint: Two edges are joined together. Common in thin sheet metal work.

The choice of weld joint depends on factors such as the type of metal, the required strength, and the accessibility of the joint during welding. A structural engineer would carefully select the most suitable joint for a particular application based on stress analysis and safety requirements.

Essential variables in welding are parameters that significantly impact the weld’s mechanical properties and quality. If these variables are not controlled precisely, it can affect the weld’s strength, toughness, and overall integrity, leading to potential failure. These variables are critical to the qualification process (PQR). Think of them as the most crucial ingredients in a recipe; getting them wrong will ruin the dish.

Examples of essential variables include:

• Welding process: e.g., Gas Metal Arc Welding (GMAW), Shielded Metal Arc Welding (SMAW)
• Base material: The type and grade of metal being welded.
• Filler material: The type and grade of filler metal used to create the weld.
• Preheating temperature: Temperature of the base material before welding.
• Welding current and voltage: Electrical parameters crucial for arc stability and heat input.
• Travel speed: Speed at which the welding torch moves along the joint.

Controlling these variables according to the qualified WPS is essential for creating consistently high-quality welds that meet the required specifications. Failure to do so can lead to non-conformances and potential safety issues.

Ensuring traceability of materials in welding, as per BS EN ISO 128-20, is crucial for quality control and liability. It’s like keeping a detailed family tree for your weld – you need to know the lineage of every component to understand its properties and potential weaknesses.

• Material Identification: Each material batch should be clearly identified with a unique identifier (e.g., heat number, lot number) that is traceable throughout the entire process. This information should be recorded on the welding procedure specification (WPS) and the welder’s performance qualification record (WPQR).
• Documentation: Maintaining meticulous records is key. This includes certificates of conformity, material test reports, and purchase orders. These documents should be easily accessible and archived securely.
• Heat Number Tracking: Each piece of material should be marked with its unique heat number. This allows you to trace its origin and properties back to the mill, ensuring consistency and quality.
• Storage and Handling: Proper storage and handling procedures are crucial to prevent material degradation or misidentification. Materials should be stored in a way that prevents contamination and ensures easy identification.

For example, if a weld fails, traceability allows us to pinpoint the specific batch of material used and investigate if any defects in the material contributed to the failure, preventing similar incidents in the future.

Verifying welder qualifications according to BS EN ISO 128-20 is a multi-step process designed to ensure welders possess the necessary skills and knowledge to produce high-quality welds. Think of it like a driver’s license test but much more rigorous and specific to welding processes.

• Written Examination: The welder needs to demonstrate a sound understanding of welding principles, techniques, and safety procedures.
• Practical Test: This involves producing a weld sample according to a specified welding procedure specification (WPS). The quality of this weld sample is then assessed through visual inspection and destructive testing (e.g., bend tests, tensile tests).
• Qualification Test: This test, sometimes referred to as a Welder Performance Qualification (WPQ) record, ensures the welder can consistently produce welds meeting the required standards. The test pieces are often subjected to non-destructive testing (NDT) techniques, such as radiographic testing or ultrasonic testing, to detect internal flaws.
• Certification: Upon successful completion of the written and practical tests, the welder receives certification, specifying the welding processes and materials they are qualified to use. This certification needs to be renewed periodically.

Failure to properly qualify welders can lead to significant safety risks and compromised structural integrity. The qualification process ensures that only competent welders work on critical components.

A welding inspector acts as the gatekeeper of quality in welding operations. They are responsible for ensuring that all welding activities comply with relevant codes, standards (like BS EN ISO 128-20), and the project specifications. They are the eyes and ears ensuring quality and safety throughout the whole process.

• Inspection Planning: They develop and implement inspection plans that define what, when, and how inspections will be carried out.
• Procedure Review: They review and approve welding procedure specifications (WPS) and welder performance qualification records (WPQR) to ensure they meet the required standards.
• Visual Inspection: They conduct visual inspections of welds to identify any surface defects.
• Non-Destructive Testing (NDT): They oversee and interpret results from NDT methods such as radiographic testing (RT), ultrasonic testing (UT), or magnetic particle inspection (MPI) to detect internal defects.
• Documentation Review: They review and verify the accuracy and completeness of all welding-related documentation.
• Corrective Actions: They identify and report any non-conformances and help implement corrective actions.

In essence, a welding inspector ensures that the final product is safe, reliable, and meets the specified quality requirements. Their role is critical in preventing failures and ensuring structural integrity.

BS EN ISO 128-20 contributes significantly to overall product safety by establishing a comprehensive framework for welding quality management. It’s the rulebook that ensures welds are strong, reliable, and won’t fail unexpectedly.

• Standardization: The standard provides a standardized approach to welding, minimizing inconsistencies and potential errors.
• Qualification Requirements: It defines stringent requirements for welder qualification, ensuring that only competent individuals perform welding tasks.
• Procedure Control: It emphasizes the importance of documented welding procedures (WPS), ensuring consistency and repeatability.
• Inspection and Testing: It outlines requirements for inspection and testing, allowing for the early detection and correction of defects.
• Traceability: It promotes traceability of materials and processes, making it possible to identify the root cause of failures.

By adhering to BS EN ISO 128-20, manufacturers can significantly reduce the risk of weld failures, leading to improved product safety and reliability. A failure in a welded joint could have catastrophic consequences; this standard helps to mitigate those risks.

Documenting welding processes is absolutely vital for ensuring consistency, traceability, and ultimately, safety. Think of it as a recipe for building a strong and reliable weld; without it, you’re just guessing.

• Traceability: Proper documentation allows for complete traceability of materials, processes, and personnel involved in each weld. If a problem occurs, you can easily trace it back to its origin.
• Consistency: Documented procedures ensure that welds are produced consistently, meeting the required quality standards. This prevents variations in quality between different welders or batches.
• Auditing and Compliance: Well-maintained records are essential for audits and compliance with relevant regulations and standards. They provide evidence that welding activities are performed according to specifications.
• Problem Solving: If a weld fails, detailed documentation helps to identify the root cause and implement corrective actions to prevent similar failures in the future.
• Training and Knowledge Transfer: Documentation serves as a valuable training resource for new welders, ensuring consistent standards are maintained across the workforce.

In short, thorough documentation is the backbone of a robust welding quality management system. It’s an investment in safety, reliability, and long-term success.

During a project involving the welding of high-strength steel pipes for a critical pressure vessel, we encountered a high rate of porosity in the welds. This was a major concern as porosity significantly compromises the structural integrity of the pressure vessel. We initially suspected the welding procedure, the welder’s technique, or the material itself.

Problem-Solving Steps:

• Root Cause Analysis: We began by systematically investigating each potential cause. We re-examined the WPS, closely inspecting the welder’s qualification records and the material certifications. This involved reviewing the welding parameters, electrode type, and preheating temperatures specified in the WPS. We visually inspected the weld and performed a thorough metallurgical analysis on samples. We also looked at storage and handling practices for the steel pipes.
• Testing and Verification: We conducted further testing including chemical analysis of the weld material and a more comprehensive NDT examination. We determined that the porosity was likely linked to the inclusion of moisture in the welding process.
• Corrective Action: After determining the cause, we implemented several corrective actions. This included: implementing strict preheating procedures to control moisture content, utilizing a drying oven for the electrode, and re-training the welders on best practices to avoid moisture ingress in the joint preparation.
• Monitoring and Verification: We monitored the welds closely during the subsequent welding operations using NDT techniques, ensuring that the implemented corrective actions were successful in resolving the issue. Once confidence was restored, the project was able to proceed without further issues.

This experience highlighted the importance of thorough investigation, detailed documentation, and collaborative problem-solving when dealing with welding-related challenges. It also reinforced the critical role of the welding inspector in identifying and resolving quality issues.