Standards and quality inspection for industrial materials: From certificates to acceptance inspection

A batch of material may have complete certification and match the ordered grade, yet disputes can still arise during acceptance inspection. Two parties may measure the same steel plate with the same measuring tool and reach different conclusions simply because the measurement conditions are not the same.

For industrial materials, documentation, test methods and operating data represent different layers of evidence. Each layer answers a different set of questions.

This knowledge series provides an overall framework for correctly interpreting and using inspection certificates, test methods, tolerances, traceability data and acceptance criteria.

1. Three layers of evidence must be considered separately

Screenshot 2026 09 22 125726 — **CO certificate (***Image: thyssenkrupp)*

When evaluating a material batch, three layers of evidence should be distinguished because they answer three different questions.

Evidence layer	Question to answer	Evidence used
Identification and traceability	What is the material and where did it come from?	Inspection certificate, identification number, batch number and traceability chain
Properties and test results	What properties does the material have, and how were the values determined?	Certificates, test standards, test reports, tolerances and measurement conditions
Operating performance	How long does the material remain in service at the actual operating position?	Baseline data and actual measurements before and after the material is put into operation

These three layers of evidence are connected, but they do not replace one another.

Certificates and traceability records help identify what material was delivered and which batch it belongs to. Test methods, standards and measurement conditions show how material properties were determined and verified. Service life, however, can only be evaluated using data from the actual operating position.

A material batch that fully complies with its certificates is therefore not, by itself, evidence that the material is suitable for a particular application or will achieve a specific service life. If no baseline was established before the material was replaced, the plant will also lack the data required to determine how much improvement the new solution actually delivers.

2. Distinguishing CO, CQ and inspection certificates

CO and CQ are widely used terms, but their functions are still frequently confused. It is therefore important to distinguish what each document actually represents.

CO relates to the origin of the goods.

CQ is commonly used to refer to documentation concerning product quality or product properties. However, the term alone does not specify who confirms the information, on what basis the tests were performed, or whether the data is linked to the actual batch delivered.

For metallic products, EN 10204 classifies inspection certificates according to the basis of validation and the type of inspection.

For this reason, when specific evidence is required, a general statement such as “CQ required” is not sufficient. The required type of inspection certificate should be specified.

Further details on certificate types and the evidential value of each document are provided in Part 1: What do material certificates and documents prove.

3. Classifying the level of assurance behind material data

A common mistake when reading a material data table is to focus on the numerical value while overlooking how that value is declared.

A value may fall into one of three categories:

Declaration level	Meaning	How it should be used
Guaranteed value	The manufacturer is responsible for the declared value	May be considered for inclusion in acceptance criteria
Typical value	Reference value only, not guaranteed	Use for guidance, not as an acceptance criterion
Converted value	Value derived from another measurement	Should not be treated as a directly measured value

In some data tables, yield strength may be stated only as a typical value rather than a guaranteed value. For certain thinner thickness ranges, hardness may not be measured directly but instead converted from tensile strength.

This directly affects the acceptance criteria. If a quality department uses a typical value as a mandatory acceptance limit, the supplier may respond during a dispute that the value was provided only for reference and was not guaranteed.

Before including a numerical value in a contract or acceptance criteria, at least three questions should therefore be answered:

At what declaration level is the value stated?
Which test method was used to determine it?
If the value relates to toughness, at what temperature was the test performed?

Without this information, a numerical value alone does not provide sufficient basis for an acceptance decision.

4. Information that needs to be clarified before ordering

Some information cannot be requested only after the material has already arrived at the warehouse.

This is because certain tests or delivery conditions must be specified before production.

Information to clarify	Related standard	Why it matters
Type of inspection certificate	EN 10204	The default certificate may not be the type required by the plant
Tolerance class	EN 10029	If not specified in the order, the supplier may provide the standard tolerance class rather than the highest-accuracy class
Ultrasonic inspection of internal soundness	EN 10160	Available only if agreed in advance
Impact testing at a specified temperature	EN ISO 148-1	Test temperature affects the result obtained
Surface and edge quality class	EN 10163-2	May affect machining, bending and welding

Impact testing requires particular attention.

A toughness value without the corresponding test temperature does not provide sufficient information for comparison.

For destructive testing, the sampling position and sampling direction may also need to be specified where these factors are important to the application.

These requirements are covered in more detail in Part 2: Test methods and material quality inspection.

5. No single standard covers the entire acceptance inspection process

Each technical question needs to be checked against the appropriate standard and corresponding method.

Question to answer	Standard	Inspection function	Inspection method
What type of inspection certificate is provided?	EN 10204	Quality department	Verify the certificate type stated on the document
Brinell hardness	EN ISO 6506-1, EN ISO 6508-1	Quality department	Portable hardness tester, on a ground and flat surface
Vickers hardness	EN ISO 6507-1	Laboratory	Cannot be checked in the workshop, must be specified in the order
Rockwell hardness	EN ISO 6508-1	Laboratory	Check whether the declared value is guaranteed or typical
Yield strength, tensile strength, elongation	EN ISO 6892-1	Warehouse, quality department	Ruler, square, flat table, measurement at the specified distance from the edge
Impact toughness	EN ISO 148-1	Laboratory	Available only if specified in the contract
Metallic material bend test	ISO 7438	Warehouse	Visual inspection, checking and edge measurement
Tolerances for hot-rolled steel plate	EN 10029	Installation team	Compare with approved reference images
Tolerances for continuously hot-rolled flat products	EN 10051	Warehouse	Inspect before the material is accepted into storage

In addition to standards used for batch acceptance inspection, this knowledge system also refers to other standards for wear classification, wear testing, steel materials and fabrication.

Content group	Standards used
Wear classification and wear testing	DIN 50320:1979-12, DIN 52108, ASTM G65, ASTM C704
High-strength steel	EN 10025-6, EN 10149-2
Welding and fabrication	EN 1011-2, EN ISO 3834-2, EN 14700

Three points should be kept in mind when using standard numbers.

First, the correct part of the standard needs to be identified. Some standards consist of multiple parts covering different product types or test conditions.

Second, the current status of the standard needs to be checked. DIN 50320:1979-12 has been withdrawn and is used in this knowledge system only as a framework for classifying wear mechanisms, not as a basis for acceptance inspection.

Third, the material scope needs to be checked. A test result obtained using a method intended for non-metallic inorganic materials should not be placed directly alongside a steel test result as though the two values were equivalent.

Standards may be revised over time. Before including a standard number in a contract or acceptance inspection record, the currently applicable version should be verified.

6. The same material can produce different results when tested differently

A test result does not depend on the material alone.

It also depends on:

test method
measurement scale
sampling position
sampling direction
sampling depth
test temperature
surface condition
equipment used

For example, Brinell and Rockwell both measure hardness, but their results cannot be converted with absolute accuracy for every material.

When comparing two batches, it is therefore more appropriate to use the same hardness scale and the same measurement conditions rather than repeatedly converting between different scales.

Portable measuring instruments also have measurement error compared with laboratory testing.

Workshop measurements can be useful for screening or detecting abnormalities. However, before using them as the basis for final acceptance inspection, the measurement error of the equipment and the test conditions need to be understood.

Further details are provided in Part 2: Test methods and material quality inspection.

7. Correct measurement requires more than the correct tool

One common source of dispute is that both parties use the same measuring tool but do not measure under the same conditions.

When evaluating tolerance and flatness, at least the following should be agreed:

applicable standard and version
specified tolerance class
measurement position
distance from the edge
reference length
supporting surface
measuring equipment

If one party measures close to the edge while the other measures at the position specified by the standard, the results may differ.

If the plate is placed on a surface that is not sufficiently flat, the supporting surface itself may affect the flatness assessment.

For this reason, a report that states only “pass” or “fail” does not provide enough information for later verification.

These principles are discussed in detail in Part 3: Material tolerances and measurement methods for acceptance inspection.

8. Traceability needs to extend from the documentation to the actual material in use

Having documentation does not necessarily mean that the traceability chain remains intact.

The chain can be broken when:

one plate is cut into multiple components
grinding or machining removes the identification number
remnant material is returned to storage
the material passes through multiple intermediate stages

For steel plate, the identification number marked directly on the material is an important link between the physical plate and its documentation.

Paint markings and labels may support warehouse identification, but they do not provide the same level of traceability.

Identification	Role
Identification number on the material	Important evidence linking the material back to its source
Documentation matching the identification number	Links the material to the batch data
Paint marking	Supports identification
Label or tag	Supports identification

When one plate is cut into several components, the relationship between the original identification number and a temporary identification number should be established before the plate is divided.

Without this step, the fabricated component may no longer contain sufficient information to trace it back to the original plate.

The detailed process is covered in Part 4: Traceability and identification of material from an incorrect source.

9. Acceptance inspection and material selection involve different responsibilities

A material may fully comply with its certificate and still be unsuitable for the specific operating position where it has been selected.

When asking who is responsible if a problem occurs, the issue should therefore be divided into three separate questions:

Question	Responsibility
Does the material match the declared specification?	Manufacturer and certificate
Is the material suitable for the specific position?	Person responsible for material selection
Were cutting, welding, fixing and installation performed correctly?	Installation contractor

These are three different layers of responsibility.

If they are not separated from the beginning, a situation may arise in which the manufacturer confirms that the material complies with its certificate and the installation contractor confirms that the work followed the required procedure, yet responsibility for selecting that material for the specific position remains unclear.

The material selection decision should therefore include:

input data
basis for the selection
responsible person
acceptance criteria
measurement data after the material is put into operation

Further details are provided in Part 5: Acceptance criteria and responsibility for material selection.

10. Acceptance criteria need to provide a verifiable basis for inspection

Not every requirement written into a document can automatically become an acceptance criterion.

At a minimum, each criterion should define:

numerical value and unit
identified test method
declaration level
who performs the measurement and where it is performed
material group to which the criterion applies

The fifth point is particularly important.

A criterion that is valid for structural steel may not be appropriate for a hardfacing layer. Similarly, a requirement developed for metallic materials may not be suitable for ceramics or other non-metallic materials.

Before a requirement is included in the acceptance criteria, the material group to which it applies should therefore be clearly identified.

If the scope of application is not defined, an acceptance criterion may incorrectly reject a material that is performing according to its intended design characteristics.

11. Common mistakes to avoid when preparing acceptance inspection documentation

No.	Mistake	Resulting issue
1	Treating a certificate as evidence of service life	A certificate does not reflect operating performance at the actual position
2	Failing to specify the tolerance class in the order	The material may be supplied to a class different from the actual requirement
3	Failing to request ultrasonic inspection in advance	The required result may not exist once the material has been delivered
4	Using a typical value as a mandatory limit	A typical value does not have the same basis as a guaranteed value
5	Comparing two materials using different hardness scales	The two values are not fully equivalent
6	Using a toughness value without recording the test temperature	A key test condition is missing
7	Measuring flatness under different conditions	The two parties may obtain different results
8	Treating paint markings as traceability evidence	Paint markings support identification only
9	Accepting material into storage when the document number does not match the identification number	The traceability chain is broken
10	Referencing a standard without checking the applicable version	A revised, replaced or no longer suitable version may be used

Some of these errors need to be prevented before the order is placed. Once the material batch has been produced or delivered, not every missing item of data can be created retrospectively.

12. Six detailed articles in this knowledge series

The Standards, Certification and Inspection knowledge series consists of six detailed articles. The series progresses from interpreting certificates and material data to test methods, tolerances, traceability, acceptance criteria and situation-based inspection procedures.

Part 1: What do material certificates and documents prove?

Part 1 explains the types of documents commonly used when purchasing and accepting materials, and how they differ according to who validates them, the basis of inspection and the degree to which they are linked to the actual batch delivered.

The article also helps identify information that needs to be clarified before ordering, particularly the required type of inspection certificate.

Certificates help establish what the material is and what data is associated with the batch. They do not, by themselves, demonstrate that the material is suitable for a specific application or will achieve a particular service life in operation.

Part 2: Test methods and material quality inspection

Part 2 focuses on how a numerical value in material documentation is generated and how that value should be interpreted.

The article covers destructive testing, non-destructive testing (NDT), Brinell and Rockwell hardness testing, tensile testing, impact testing, ultrasonic inspection, and sampling position and direction.

Two results are meaningfully comparable only when the test methods and test conditions are compatible. The numerical value should therefore not be considered separately from the method used to generate it.

Part 3: Material tolerances and measurement methods for acceptance inspection

Part 3 covers tolerance classes, measurement positions, distance from edges, reference length, supporting surfaces and the conditions that need to be agreed before measurement results are evaluated.

This section helps address situations where two parties measure the same material but reach different conclusions.

Before determining that a material does not comply, it is necessary to check whether both parties are using the same standard, the same tolerance class and the same measurement conditions.

Part 4: Traceability and identification of material from an incorrect source

Part 4 follows the traceability chain from the batch number and identification number on the material through to the associated documentation and fabrication records.

The article also explains how traceability can be maintained after a plate is cut into multiple components, particularly when identification markings may be removed during cutting, grinding or machining.

Traceability does not end at receiving inspection. The traceability chain needs to continue through to the actual material or component that is put into service.

Part 5: Acceptance criteria and responsibility for material selection

Part 5 separates three areas of responsibility that are often confused: whether the material matches its declared specification, whether the material is suitable for the intended operating position, and whether machining, fixing and installation have been carried out correctly.

The article also explains what an acceptance criterion needs to include in order to provide a sufficient basis for inspection, including the value, unit, test method, declaration level, responsible party and applicable material scope.

Whether a material is suitable for a specific operating position is a separate technical decision that requires input data, a documented basis for selection and an identified responsible person.

Part 6: Material inspection and acceptance inspection procedures for different situations

Part 6 connects the topics covered throughout the knowledge series and organizes them into practical workflows for different situations.

The article focuses on three main cases:

preparing to place an order
material has just arrived at the warehouse
a difference or dispute has arisen over measurement results

Each situation requires a different starting set of data and evidence. The next step should therefore be determined by what information is missing at that point, rather than applying the same procedure to every case.

13. Where should you start?

The six parts do not necessarily need to be read in sequence when addressing a specific task.

Situation	Content to prioritize
Preparing an order	Part 1, Part 2 and Part 3
Material has just arrived at the warehouse	Part 1 and Part 4
Measurement results differ	Part 2 and Part 3
Developing acceptance criteria	Part 1, Part 2 and Part 5
Determining responsibility for material selection	Part 5
Unsure where to begin	Part 6

The highest priority remains the stage before ordering.

The inspection certificate type, tolerance class and certain tests can only be properly arranged when the requirements are defined from the beginning.

14. Notes on applying this knowledge

First, standards may be revised, replaced or withdrawn over time. Before including a standard number or threshold in a contract or acceptance inspection record, the currently applicable version should be checked.

Second, this knowledge series focuses on technical evidence and the organization of the acceptance inspection process. It does not interpret responsibility under Vietnamese law. Legal or contractual responsibility should be assessed separately.

Third, measurements taken with portable instruments are subject to measurement error and depend on the conditions under which they are performed. A quick workshop measurement should not automatically be treated as a complete substitute for a standardized laboratory test.

Fourth, certificates and traceability do not demonstrate service life at a specific operating position. Evaluating operating performance requires baseline data and follow-up measurements from the actual equipment.

Fifth, the receiving inspection checklists, common points where the traceability chain may be broken, and methods for organizing records in this knowledge series are based on Gia Anh’s working experience. They support the inspection process but are not presented as requirements of a separate standard.

A well-structured acceptance inspection record should do more than confirm whether the material matches its documentation. It should allow the reviewer to trace what requirements the material was ordered against, how each value was determined, which batch the actual material came from, who made the material selection decision, and what operating data was used to verify the result after installation.