The notion that welding will produce a certain percentage of defective welds is nonsense.  Welds don’t become defective on their own.  Defective welds are produced because mistakes are being made.  Mistakes can be prevented and therefore so can defective welds.  The key is welding quality, not welding inspection.  Welding Quality is achieved by doing it right the first time.  Whatever it is. It may be selecting the correct welding process, electrode or filler metal, or designing a correct weld joint, etc.  The goal being to design and build in welding quality with the support of the welding quality system. The welding quality system is all about traceability.  That is, it must document who did what, when, where and how.

Therefore, the welding quality system is a system of written policies, procedures, instructions, and check lists used to document and control the drawings, specifications, procedures, materials, processes, examinations, tests, inspections, calibrations, etc., related to welding activities, to ensure that the correct information gets to those who will use it, and provide a record of what was done, by whom, when, where and how.

These controls help to design and build in welding quality by avoiding mistakes, and thereby ensure that the weldment is designed and fabricated in accordance with established requirements.

The requirements may come from laws, regulations, codes, standards, specifications, engineering drawings, customer, or original design concepts.

The quality engineer is responsible for setting up and maintaining the overall quality system for the company or organization, and the welding engineer is responsible for providing input for the welding quality section of the system.  The welding quality system must contain the following elements as a minimum:

Top management must establish and document the policy regarding the overall quality system, and organizational relationships, and responsibilities.

The policies and organizational relationships must promote an atmosphere and environment conducive to quality.

Within the organizational relationships, welding inspectors and other quality personnel must have the authority to make quality decisions that are independent and final.

That is, welding inspectors and quality personnel must not report to those who are responsible for designing and fabricating the weldment.

The organizational structure and policies contribute to designing and building in welding quality.

The design function has the overall responsibility for research, development, design and related engineering necessary to develop a concept into an actual weldment.  To be successful the design activity requires a multi-discipline team of engineering specialists working concurrently to design quality into the weldment.  To accomplish this, the  design team must include the designer, welding engineer, metallurgical or materials engineer, quality engineer, fabrication engineer, and others as required.  Specifically, the weldment design process determines:
Applicable codes and standards
Service life, load types, and stresses
Operating temperatures, pressures, and environments
Selection, application, and specification of materials for the design conditions
Documentation of the design in specifications and drawings

The welding engineer supports the design function by establishing and specifying welding requirements, answering technical welding questions, and advising on matters of welding.  No other engineering discipline understands the depth and breadth of the science of welding and joining materials, and the complex microstructure and property changes taking place in the weld and heat-affected zones, more than a person with a welding engineering degree.  Therefore, to ensure that welding quality is designed in, the welding engineer assists with:
Weldment design review
Weld joint design (type and geometry)
Weld joint and weld location and sizes
Welding process selection
Materials selection, processing, and specification
Destructive and nondestructive testing method selection
Engineering drawing details related to welding and materials
Welding code, standard, and specification interpretation
Welding quality system (Quality Assurance and Quality Control)
Welding costs and economics
Welding safety requirements

The welding engineer also writes the welding specification which specifies:
Materials to be welded
Welding processes to be used
Electrodes and filler materials to be used
How to qualify welding procedures
How to qualify tackers, welders, and welding operators
Scope, terms, definitions, and applicable documents
special requirements for fabrication, materials, and welding
Quality, inspection, workmanship, and acceptance criteria

The procurement function uses the engineering specifications and drawings produced by the design function to make purchases.

To ensure welding quality, procurement documents must be reviewed by the welding inspector or quality engineer for inclusion of the correct welding requirements.

Using the correct engineering documents produced by the design function and verification by the quality organization contributes to building in welding quality.

As required the welding engineer must be available to provide assistance with:
Purchasing documents for welding and base materials
Welding and fabrication equipment purchasing
Subcontractor selection, qualification, auditing, surveillance

The receiving function is responsible for verifying that those materials and items received are in accordance with the procurement documents.

To ensure welding quality, the welding inspector or quality engineer must perform receiving and/or source inspection to verify that purchased materials and items received are in conformance with procurement and engineering document requirements.

The receiving activity contributes to building in welding quality.

The fabrication function uses engineering documents produced by the design function to determine the most economical methods, tools, equipment and facilities, needed to build quality into the weldment.

After this determination and prior to fabrication and welding, the welding engineer writes, develops, and qualifies the necessary welding procedures.

Also prior to fabrication and welding, the welding inspector qualifies welders and welding operators using the qualified welding procedures, in addition to reviewing drawings, specifications, procedures, qualifications, mill test reports, material identification, welding equipment etc., to verify conformance to requirements.

During fabrication and welding, the welding inspector must verify that the weldment is being fabricated and welded in accordance with established requirements.

After fabrication and welding, the welding inspector must provide records, reports, and other documentation as proof that the weldment has been fabricated and welded in accordance with established requirements.

The inspection activity verifies that quality is and has been built into the weldment.