How can the quality of welded joints be reliably demonstrated and which procedure offers the highest level of safety?
This question arises daily in the metalworking industry whenever the qualification of welding procedure specifications is concerned. The following article explains the normative test procedure DIN EN ISO 15614-1 from the ground up and shows when the use of this comprehensive qualification method is truly necessary.
The standard is one of several normatively recognised options for qualifying a preliminary welding procedure specification (pWPS). However, it is regarded as the most thorough and at the same time the most demanding procedure.
Many sets of rules use this qualification basis for the highest requirements. But when does the benefit justify the considerable cost and time expenditure?
The answer depends on the application code, on the materials used and on the degree of mechanisation. This guide makes the complex relationships understandable even for beginners and helps with making the right decision.
- DIN EN ISO 15614-1 is one of five recognised methods for qualifying welding procedure specifications
- The procedure is regarded as the most comprehensive but also the most cost-intensive qualification system
- Numerous international codes use this standard as a qualification basis
- Its application is particularly required for special materials or a high degree of mechanisation
- A careful assessment of the necessity helps to avoid unnecessary costs
- The procedure follows clear normative requirements and offers the highest level of safety
- Even people without in-depth welding knowledge can understand the basic principles
What is the DIN EN ISO 15614 standard?
DIN EN ISO 15614 defines clear requirements for the qualification of welding procedures. This international standard provides the basis for systematic welding process validation in the metalworking industry. It ensures that welded joints meet the required quality standards and remain reliable in the long term.
Part 1 of the standard in particular is of great practical importance. It applies to arc and gas welding of steels as well as arc welding of nickel and nickel alloys. DIN EN ISO 15614-1 thus covers the most common welding procedures in industrial manufacturing.
Fundamentals of welding procedure testing
The aim of welding procedure testing is the standard-compliant demonstration that a welding procedure reproducibly produces suitable welded joints under defined conditions. This demonstration is provided by a WPS qualification that documents all relevant parameters.
Metallic materials react differently to welding processes. Each procedure must therefore be tested individually. The standard defines precisely which conditions must be observed and which tests must be carried out.
Welding process validation protects against later problems. Defective welded joints can lead to component failure. Careful testing before production use effectively prevents such risks.
The scope of testing depends on the subsequent application. Safety-critical components require more extensive tests than less heavily loaded structures. The standard takes these different requirements into account through a flexible system.
Layout and structure of the standard
After years of international coordination, an innovative two-level model was introduced. This model combines different testing philosophies and creates greater flexibility. It enables economical qualification while ensuring quality.
Level 1 is based on North American ASME regulations. It requires a basic scope of testing, which comprises the following tests:
- Visual testing to detect surface defects
- Transverse tensile test to assess strength
- Transverse bend test to assess ductility
Level 2 represents the European requirements with considerably more extensive testing. Here additional procedures are used:
- Radiographic testing for internal defect analysis
- Surface crack testing with high sensitivity
- Notched-bar impact testing to assess toughness
- Hardness testing in the weld zone
- Macro-section examination of the seam structure
If no level is specified at the time of order placement, the requirements of Level 2 automatically apply. This default rule ensures that an adequate quality level is always achieved. It prevents misunderstandings between the client and the performing company.
Difference between WPS and WPQR
The terms WPS and WPQR are frequently confused. Yet both documents fulfil fundamentally different functions within the qualification system. A clear understanding of this distinction is indispensable for a successful WPS qualification.
WPS stands for Welding Procedure Specification. It serves as a concrete work instruction for the welder. The WPS describes step by step how a welded joint is to be produced.
The WPQR, on the other hand, means Welding Procedure Qualification Record. This document records the qualification test that was carried out, with all relevant details. It contains all welding parameters and the complete test results.
The relationship between the two documents is clearly defined. The WPQR forms the basis for the WPS. Only after successful testing and documentation in the WPQR can a WPS be created and released.
In practice this means: the WPQR proves that a procedure works. The WPS explains to the welders how to apply this tested procedure correctly. This clear separation creates transparency and legal certainty for all parties involved.
Why carry out a WPS qualification?
Many companies ask themselves why they should invest time and resources in a WPS qualification. The answer lies in the many benefits that systematic welding process validation brings with it. A qualified welding procedure specification forms the foundation for reliable and safe welding work.
In numerous codes, DIN EN ISO 15614 is used as a qualification basis. The decision in favour of such a test should, however, be well considered and take into account the specific requirements of the respective project.
Consistent quality and maximum safety
A qualified welding procedure specification guarantees a consistently high weld seam quality across all manufacturing processes. Through systematic testing, potential weak points are identified at an early stage. These can be remedied before they lead to costly problems in series production.
This aspect is of decisive importance, especially for safety-relevant components. Pressure vessels, bridge structures and rail vehicles require the highest safety standards. A defective weld seam can have serious consequences here.
Those who have their welding procedures certified invest in the safety of the end products. Qualification in accordance with DIN EN ISO 15614 creates confidence in the reliability of the welded joints.
Economic benefits of welding process validation
The initial test does involve costs, yet this investment pays for itself quickly. Rework, scrap and complaints cause far higher costs than a one-off qualification. A qualified welding procedure specification considerably reduces these risks.
Further economic benefits include:
- More efficient planning and execution of welding work
- Reduced uncertainties in the manufacturing process
- Shorter production times through optimised workflows
- Lower testing costs in ongoing production
- Increased competitiveness through demonstrable quality
For cost reasons, qualification should only be chosen when the application code or the supply agreement makes it necessary. The material or the degree of mechanisation can also make such a test necessary.
Legal requirements and customer demands
Many industrial sectors place normative requirements on welding procedures. Pressure equipment construction, railway technology and steel construction are just a few examples. In these areas, a welding approval is often indispensable.
Customers increasingly demand proof of qualified welding processes as part of their supply conditions. Without appropriate qualification, many contracts in regulated areas remain out of reach. Certification thus creates legal certainty and opens up new business opportunities.
Independent testing bodies support their customers with regard to a sensible testing concept. They point out necessities and offer their help with planning. Engaging an accredited testing laboratory considerably increases confidence in the quality of testing.
An accredited welding approval creates far greater acceptance among customers and clients. Professional documentation by recognised testing bodies considerably increases the credibility of the qualification.
Fields of application and affected industries
Welded joints form the backbone of modern manufacturing industries, which is why standard-compliant testing has become indispensable in many areas. DIN EN ISO 15614 defines the requirements for weld seam testing across various economic sectors. Depending on the field of use and safety relevance, the specific testing requirements vary considerably.
Industries with mandatory qualification requirements
Pressure equipment construction is among the areas with the strictest requirements for welding procedure testing. The European Pressure Equipment Directive prescribes harmonised standards in order to ensure the highest safety standards. Vessels and pipelines under pressure require seamless qualification of the welding processes used.
In railway technology, specific requirements under EN 15085 apply. This standard requires comprehensive weld seam testing for rail-bound vehicles and their components. The high loads in railway operation make careful process validation indispensable.
Steel construction is subject to EN 1090, which likewise requires welding procedure tests in accordance with DIN EN ISO 15614. Load-bearing structures such as bridges, high-rise buildings and industrial facilities require certified welding procedures. The certification obligation ensures structural integrity over the entire service life.
Further affected industrial sectors include:
- Pipeline construction for the transport of media under various conditions
- Offshore industry with extreme environmental loads from seawater and weather
- Shipbuilding for merchant ships and special vessels
- Aerospace with the highest quality demands
- General mechanical engineering with varying requirements depending on the application
Power plant construction places particularly high demands due to extreme operating conditions. High temperatures, pressures and corrosive media require specially qualified welding processes. The petrochemical industry likewise demands intensive qualification measures because of the hazardous substances and process conditions.
Covered welding processes and material groups
The standard applies to arc and gas welding of steels as well as to arc welding of nickel and nickel alloys. The arc welding procedures covered include several established processes. Manual metal arc welding still forms an important foundation in many manufacturing areas.
Metal active gas welding and metal inert gas welding are among the most common industrial procedures. Tungsten inert gas welding enables precise weld seam testing for demanding joints. Submerged arc welding is used above all for thick-walled structures.
Gas welding is also covered, but plays a subordinate role in modern manufacturing. The qualification covers various welding positions and seam forms. Each procedure requires specific test parameters and documentation.
In terms of materials, the standard covers a broad spectrum. Non-alloy structural steels form the basis of many structures. High-strength fine-grained structural steels are used for particularly stressed components.
Creep-resistant and heat-resistant steels are used in power plants and process facilities. Chromium-nickel steels offer corrosion resistance in aggressive environments. Nickel and nickel alloys extend the range of use to extreme conditions.
The systematic grouping of the materials is carried out in accordance with ISO/TR 15608. This material grouping makes it possible to cover a defined range of validity with a single test. For materials in accordance with ISO/TR 20172, ISO/TR 20173 or ISO/TR 20174, these alternative grouping systems must be applied.
The table for nickel and nickel alloys has been extended to include dissimilar joints. Joints between nickel and nickel alloys against steel are now also covered. This extension takes account of the increasing importance of material combinations.
Welding procedure testing in accordance with DIN EN ISO 15614 in detail
The practical implementation of welding procedure testing is divided into several consecutive phases. Each step builds logically on the previous one and, in the end, leads to a qualified welding procedure specification. The entire process is structured and documented by clear requirements.
Preparation and planning of the test
At the beginning stands the creation of a preliminary welding procedure specification, also known as pWPS. This defines all important welding parameters for the subsequent execution. It serves as a guideline for the entire test process.
The pWPS contains essential information about the materials used. This includes the exact designation of the base materials and the selection of suitable welding consumables. The seam form and seam geometry are also defined here already.
Important temperature values must be specified in advance. The preheating temperature and the interpass temperature considerably influence the quality of the weld seam. The heat input is calculated and documented in the pWPS.
A fundamental decision concerns the choice of test level. Level 1 comprises visual testing, transverse tensile test and transverse bend test as mandatory. Level 2 additionally requires radiographic testing, surface crack testing, notched-bar impact testing, hardness testing and macro-section examination.
The preparation of the test pieces requires careful planning. They must be large enough to allow all required specimens to be taken. The dimensions depend on the planned test procedures and the welder qualification.
Execution of the weld seam test
A qualified welder carries out the actual welding. He works strictly in accordance with the requirements of the preliminary welding procedure specification. Any deviation would jeopardise the validity of the test.
During the welding work, all parameters are continuously monitored. Current, voltage and welding speed must be recorded. Compliance with the temperatures is also documented seamlessly.
An examiner or a recognised testing body verifies the entire process. Verification does not necessarily mean that someone is constantly present. Suitable records and random samples can likewise fulfil this task.
After completion of the welding, a post-weld heat treatment may be necessary. This depends on the material properties and the standard requirements. Only afterwards does the actual testing phase begin.
Destructive and non-destructive tests
The non-destructive tests are used first. They allow defects to be located without damaging the test piece. Visual inspection examines the weld seam for externally visible defects.
In Level 2, radiographic testing is part of the mandatory programme. It makes internal defects such as pores or inclusions visible. Surface crack testing detects fine cracks that are not recognisable with the naked eye.
An important note applies to the assessment of non-destructive tests: at both ends of the weld seam, 25 mm each are disregarded. This run-off is not included in the assessment for butt joints on plate and for T-joints.
The destructive tests provide detailed characteristic values for the weld seam. For this purpose, various specimens are taken from the test piece. Each specimen serves a specific testing purpose.
The transverse tensile test determines the strength of the joint. The bend test tests the deformability of the welded material. These two tests are prescribed for both levels.
The notched-bar impact test measures the toughness at various temperatures. In procedure tests, a striker with a 2 mm radius is always used. This test is only required for Level 2.
The hardness test records values in three different areas. Measurements are taken in the weld metal, in the heat-affected zone and in the unaffected base material. In this way, undesired hardening can be identified.
The macro-section examination often concludes the tests. It shows the internal structure of the weld seam and reveals lack-of-fusion defects. All determined values must comply with the limit values of the standard.
Only when all tests have been successfully passed is the procedure test deemed complete. The results are recorded in a report. This forms the basis for the final welding procedure specification.
Essential and non-essential changes
A central question in practice concerns the distinction between essential and non-essential changes to the welding process. After successful qualification, companies want to use their welding procedures flexibly. Welding procedure testing in accordance with DIN EN ISO 15614 clearly stipulates which parameter changes are permissible and when a new test becomes necessary.
This distinction is decisive for the economical use of qualified procedures. It enables adaptations to different manufacturing situations without compromising safety.
Permissible variations within the qualification
The standard precisely defines the ranges of validity for various welding parameters. These ranges enable practical application without constant re-testing.
For material thickness, extended ranges of validity apply. For test pieces with a thickness below 3 mm, a range of 0.5 t to 2 t applies for the base material. This provision applies to both single-pass and multi-pass joints.
The thermal parameters offer defined tolerances. The preheating temperature may be lowered by up to 50 °C. The interpass temperature may be raised by up to 50 °C without a requalification becoming necessary.
An exception is formed by material groups 8, 10 and 41 to 48. Stricter requirements apply to the interpass temperature for these materials.
In Level 2 of the test, specific deviation options exist. From the determined values for the heat input, a deviation of 25 % upwards is permitted where there are requirements for impact energy. Where there are requirements for hardness, a deviation of 25 % downwards is permitted.
The seam type also offers flexibility. Butt welds automatically qualify fillet welds as well. This provision considerably simplifies practical application.
For welding consumables, a brand change is possible under certain conditions. With the same mandatory designation of a covered electrode, it is permissible to switch to a different brand name. The prerequisite is that the requirements for impact energy are not lower than –20 °C.
The material grouping in accordance with ISO/TR 15608 enables additional flexibility. A test with one material of a group can, under certain conditions, cover other materials of the same group. In doing so, the same welding consumable and identical parameters must be used.
Necessity of a renewed test
A re-test becomes necessary when the defined ranges of validity are exceeded. This serves quality assurance and compliance with safety-relevant requirements.
Fundamental changes to the welding procedure always require a new qualification. The change from manual metal arc welding to a MAG procedure represents such an essential change.
The transition to a different material group without corresponding coverage makes a re-test necessary. Exceeding the qualified thickness range also requires a renewed welding procedure test in accordance with DIN EN ISO 15614.
Essential changes to the heat management outside the permitted tolerances likewise lead to requalification. This concerns both the preheating temperature and the interpass temperature when the defined 50 °C tolerance is exceeded.
Changes to the seam type that are not covered by the existing qualification require a new test. The clear definition of these limits prevents unsafe welded joints and ensures compliance with the standard requirements.
WPQR: documentation of welding process validation
After successful completion of welding procedure testing, the WPQR is produced as the central document of the welding approval. This record demonstrates that a welding procedure achieves the required properties under defined conditions. Careful documentation forms the basis for all further welding-related activities within the company.
Procedure tests have no time limitation, provided that no essential changes are made to the procedure and the underlying standard requirements remain fulfilled. This makes the WPQR a permanent proof of qualification. Already existing tests can, if required, be transferred to new versions of the standard, provided that the current requirements are met.
Content and structure of a Welding Procedure Qualification Record
A complete WPQR contains all relevant information on the welding procedure test that was carried out. The documentation must be so detailed that the test remains traceable at any time. Only in this way does the document fulfil its function as a reliable proof.
The following core elements must be included in every WPQR:
- Identification of all parties involved, such as manufacturer, testing body and the welder carrying out the work
- Complete description of the base materials with all relevant material characteristic values
- Information on welding consumables including manufacturer information and batch designations
- Detailed parameters of the welding procedures applied
- Geometric data on the weld seam and on the test piece used
The thermal conditions form another important component. Preheating temperatures, interpass temperatures and any post-weld heat treatments must be documented precisely. These parameters significantly influence the weld seam properties.
The core of every WPQR is formed by the documented test results. All investigations carried out are recorded with their measured values. The assessment is based on the normative requirements, so that it is clearly recognisable whether the test was passed.
The range of validity of the qualification is finally described precisely. This enables an unambiguous assignment for future applications. The qualified procedure may only be used within this range.
Relationship between WPQR and WPS
WPQR and WPS stand in a clearly defined functional relationship to one another. The WPQR serves as proof of testing and forms the basis for the creation of the welding procedure specification. This relationship is essential for understanding welding-related documentation.
While the WPQR contains all test details, the WPS concentrates on production-relevant information. The welding procedure specification gives the welders concrete work instructions for daily manufacturing. However, it must move strictly within the framework of the qualified range of validity.
A single WPQR can serve as the basis for several different WPS. The prerequisite is that all welding procedure specifications lie within the qualified range. Parameters that are not covered by the qualification may not appear in the WPS.
In the case of essential changes to the welding parameters, a new qualification may become necessary. The existing WPQR then no longer covers the extended range. Where applicable, additional tests can be carried out subsequently without having to weld a completely new test piece.
Retention and welding approval
The permanent and secure retention of WPQR documents is one of the fundamental duties of every welding company. Since no time limit exists, these proofs must be available at any time. Document management therefore requires particular care.
The retention must provide protection against various risks:
- Loss due to inadequate backup or missing backup systems
- Damage due to improper storage or environmental influences
- Unauthorised changes due to a lack of access controls
- Illegibility due to ageing in the case of paper documents
Many companies today rely on electronic document management systems. These offer advantages in terms of administration and accessibility. The authenticity and integrity of the digital documents must, however, remain ensured.
Engaging an accredited testing laboratory considerably increases the basic confidence in the quality of testing. Accredited testing laboratories are assessed in Germany by DAkkS as a third party. This independent supervision creates considerably greater acceptance among customers and supervisory authorities.
Tests in accordance with DIN EN ISO/IEC 17025 by accredited bodies enjoy particular confidence. The regular surveillance by accreditation bodies guarantees consistent quality. This can bring decisive advantages in the welding approval.
With the publication of new versions of the standard, the question of the validity of existing qualifications often arises. Existing procedure tests can be described in the range of validity based on the new edition. The prerequisite is the fulfilment of the required test requirements.
WPS qualification by means of a welding procedure test remains the most demanding procedure among all available qualification methods. Companies should choose this path deliberately when other qualification procedures do not apply or when codes, materials or the degree of mechanisation require it.
The investment in a well-founded qualification pays off through process reliability and consistent quality. The systematic documentation in WPQR and WPS creates transparency for all parties involved. Experienced testing bodies support companies with sensible testing concepts and the necessary infrastructure.
Accredited laboratories offer additional security through their own surveillance. They increase the acceptance of the qualification among customers and authorities. When applied appropriately, welding procedure testing in accordance with DIN EN ISO 15614 offers a clearly structured, internationally recognised framework for high-quality and safe welded joints.
