How do you qualify a new material for use in a pressure vessel design?

To qualify a new material for use in a pressure vessel design, engineers must demonstrate that the material meets the mechanical, chemical and fabricability requirements defined by the applicable pressure equipment code, supported by documented test data and traceability records. The qualification process is not a single step but a structured sequence of verification activities that confirms a material’s fitness for the specific operating environment. The questions below walk through the key stages and considerations that govern material approval in pressure vessel engineering.

What criteria determine whether a material is suitable for pressure service?

A material is suitable for pressure service when it can be shown to have adequate strength at the design temperature, sufficient toughness to resist brittle fracture, compatibility with the process fluid, and the ability to be reliably welded and fabricated to the required geometry. These four criteria form the baseline against which any candidate material is assessed, whether it is an established grade or a novel alloy being considered for the first time.

Strength requirements are expressed through allowable stress values derived from tensile and yield strength data across the full operating temperature range. Toughness is assessed through impact testing, particularly where low temperatures are involved. Corrosion compatibility must be evaluated against the specific process chemistry rather than general guidance, since trace contaminants or concentration effects can dramatically alter corrosion behaviour. Fabricability covers weldability, formability and the ability to meet dimensional tolerances after fabrication, including any post-weld heat treatment that the material may require.

For corrosion-resistant materials such as titanium, zirconium or nickel alloys, the suitability assessment also includes confirming that the alloy grade is appropriate for the specific corrosive environment, not simply that the material family is corrosion resistant in general terms.

How does the ASME or PED code qualification process actually work?

Under ASME Section VIII and Section II, a material must either appear in the code’s approved material specifications or be qualified through a formal procedure that generates the data needed to establish allowable stress values and assign the material to an appropriate P-Number for welding qualification purposes. The PED framework in Europe operates differently, relying on harmonised European material standards, but the underlying logic is the same: the material must have a defined, verified set of mechanical properties that the designer can use with confidence.

For a material already listed in ASME Section II Part D, the allowable stress values are published and the designer can use them directly, provided the material certificate confirms conformance to the relevant specification. For a material not yet listed, the manufacturer or applicant must submit a code case application, providing test data across the temperature range, weld procedure qualification results, and evidence of fabrication experience. Code cases are reviewed by the relevant ASME committee and, once approved, allow the material to be used under defined conditions.

Under the PED, materials not covered by a harmonised standard can be used through a European Approval of Materials, which follows a comparable evidence-based review process. In both frameworks, the burden of proof rests on demonstrating performance through data rather than through assertion.

What material tests are required before a new material can be approved?

Before a new material can be approved for pressure service, the minimum required tests typically include tensile testing across the design temperature range, Charpy impact testing at the minimum design temperature, hardness testing, and chemical composition verification. Additional tests may be required depending on the material type, the operating environment and the applicable code.

The core test programme for most pressure vessel material qualifications includes:

Tensile testing: to establish yield strength, ultimate tensile strength and elongation at room temperature and at elevated temperatures if applicable
Impact testing: Charpy V-notch tests to confirm adequate toughness, particularly at low design temperatures
Chemical analysis: to verify composition against the material specification and confirm the absence of harmful trace elements
Hardness testing: to check consistency across the material and, where relevant, across weld zones
Corrosion testing: for corrosion-resistant alloys, immersion or electrochemical tests in representative process media may be required to confirm compatibility
Non-destructive examination: ultrasonic or radiographic testing to confirm the internal soundness of the base material

For clad materials, which combine a structural backing material with a corrosion-resistant inner layer, additional tests are required to verify the bond integrity between layers and the corrosion resistance of the cladding itself. The test scope is defined by the applicable code and by the specific demands of the application.

How do operating conditions affect which material properties must be verified?

Operating conditions directly determine which material properties are critical and therefore which tests must be prioritised. A material that performs adequately at ambient temperature and low pressure may be entirely unsuitable for elevated-temperature, cryogenic or high-pressure service without additional verification of properties that are not relevant at baseline conditions.

At elevated temperatures, creep behaviour becomes relevant alongside tensile strength, because a material may yield progressively under sustained stress even when peak stress remains below the nominal yield point. The code allowable stresses at high temperatures already account for this, but the designer must confirm that the specific material heat conforms to the data on which those values are based.

At low temperatures, the primary concern shifts to brittle fracture risk. Impact testing at the minimum design metal temperature is essential, and many codes require that impact test results meet defined absorbed energy thresholds before a material can be used below a certain temperature.

Where the process involves cyclic loading, fatigue behaviour must also be considered. For highly corrosive environments, stress corrosion cracking susceptibility becomes a critical property to verify, since some alloys that are corrosion resistant under static conditions can fail rapidly under combined stress and chemical exposure. The operating conditions, taken together, define the property map that the qualification programme must address.

What role does fabrication behaviour play in material qualification?

Fabrication behaviour is a central element of material qualification because a material that cannot be reliably welded, formed or heat-treated to produce a sound vessel is not practically usable, regardless of its nominal mechanical properties. Weldability is typically the most critical fabrication characteristic and is assessed through welding procedure qualification in accordance with ASME Section IX or the equivalent EN ISO standards under the PED framework.

Welding procedure qualification involves producing test welds using the proposed process parameters, then subjecting the weld and heat-affected zone to the same mechanical and non-destructive tests required for the base material. For materials with limited ductility, high hardenability or sensitivity to hydrogen embrittlement, the welding procedure must demonstrate that these risks are managed through appropriate preheat, interpass temperature control or post-weld heat treatment.

Formability is equally important for components manufactured from plate or tube, where the material must tolerate cold or hot forming without cracking or degrading its mechanical properties. Some high-strength alloys and duplex stainless steels require careful control of forming temperature and subsequent heat treatment to restore the intended microstructure. These fabrication constraints are not obstacles to material use, but they must be understood and planned for before a material is committed to a design.

When should an engineer consider a non-listed or novel material instead of a standard one?

An engineer should consider a non-listed or novel material when no standard code-listed material can simultaneously satisfy the mechanical, corrosion-resistance and fabricability requirements of the application, or when a new alloy offers a demonstrated performance advantage that justifies the additional qualification effort. This situation arises more frequently in highly corrosive, high-temperature or otherwise extreme service environments where the limitations of conventional materials are well established.

The decision to pursue a non-listed material carries a significant qualification burden. The engineer must be prepared to generate the full dataset required for a code case or material approval, including testing across the design temperature range and welding procedure qualification. This process takes time and adds cost, which must be weighed against the performance benefit.

In practice, the most common drivers for considering novel or non-listed materials are:

No listed material provides adequate corrosion resistance in the specific process chemistry
A newer alloy grade offers improved properties over the listed equivalent, particularly in high-temperature or cyclic service
Weight or dimensional constraints require a material with a higher strength-to-weight ratio than standard options provide
A technology licensor specifies a proprietary alloy or a grade not yet included in the applicable code edition

In all cases, the engineer should engage with the relevant notified body or inspection authority early in the process, since the approval pathway and timeline will affect project scheduling.

How do inspection and documentation requirements differ for newly qualified materials?

Newly qualified or non-listed materials are subject to more extensive inspection and documentation requirements than established code-listed materials, because the body of accumulated fabrication experience is smaller and the consequences of an undetected material anomaly are potentially more significant. The inspection programme must be defined at the design stage and agreed with the relevant inspection authority before fabrication begins.

For base material, the documentation requirements typically include mill certificates with full chemical and mechanical test results, traceability records linking each piece of material to its heat and lot, and confirmation that the material was produced and tested in accordance with the applicable specification. For novel materials, additional third-party verification of the mill certificate data may be required.

During fabrication, the non-destructive examination scope for newly qualified materials is generally more extensive than for standard materials. Radiographic or ultrasonic examination of welds, hardness surveys of weld zones and heat-affected areas, and ferrite content measurements for austenitic or duplex alloys are common additions to the baseline inspection plan. Post-weld heat treatment, where required, must be documented with calibrated temperature records.

The final documentation package, sometimes referred to as the manufacturer’s data report or the technical file under the PED, must demonstrate that every stage of material qualification, fabrication, inspection and testing has been completed and recorded in a traceable manner. This documentation forms the basis for the vessel’s operating life and any future inspection or repair decisions.

How Coek supports material qualification for complex pressure vessel projects

When a project involves advanced, non-standard or newly qualified materials, the fabrication partner’s role extends well beyond cutting and welding plate. Coek Engineering combines in-house mechanical engineering expertise with extensive hands-on experience in demanding materials including titanium, zirconium, Hastelloy, Inconel and clad constructions to support the full qualification and fabrication process.

For EPC contractors, technology owners and industrial end users working with technically challenging equipment, Coek’s capabilities in this area include:

Translating process requirements and material specifications into manufacturable mechanical designs
Developing and qualifying welding procedures for advanced and corrosion-resistant alloys
Managing inspection and documentation requirements in line with ASME, PED and ISO 9001 standards
Fabricating custom pressure vessels in materials that demand precision process control throughout manufacturing
Supporting clad construction projects where base material and cladding must each meet separate qualification requirements

If your project involves a material qualification challenge or requires a fabrication partner with proven expertise in advanced pressure vessel materials, contact Coek Engineering to discuss your requirements.

Frequently Asked Questions

How long does the material qualification process typically take, and how should engineers plan for it?

The timeline for qualifying a non-listed material can range from several months to over a year, depending on the complexity of the test programme, the availability of accredited testing laboratories, and the review cycle of the relevant code committee or notified body. Engineers should initiate the qualification process as early as possible in the project lifecycle — ideally during the front-end engineering phase — to avoid it becoming a critical-path constraint. Early engagement with the inspection authority and a clearly scoped test plan are the most effective tools for keeping qualification timelines predictable.

What is the difference between a material certificate and a material qualification, and why does it matter?

A material certificate (such as an EN 10204 3.1 or 3.2 certificate) confirms that a specific batch of material conforms to its stated specification in terms of chemical composition and mechanical properties. A material qualification, by contrast, is the broader process of demonstrating that a material type is fit for a specific service application under the applicable pressure equipment code. A certificate alone is not sufficient for a novel or non-listed material — it must be supported by the full qualification dataset, including test results across the design temperature range and welding procedure qualification records. Confusing the two is one of the more common documentation errors encountered during third-party inspection.

Can a material that has been qualified for one pressure vessel project be reused for a different application without repeating the full qualification process?

In many cases, yes — but only within the boundaries established by the original qualification. If the new application falls within the same design temperature range, pressure class, process chemistry and code edition, the existing qualification data can typically be referenced without repeating the full test programme. However, if the new application introduces conditions not covered by the original qualification — such as a lower minimum design metal temperature, a different corrosive medium, or a different welding process — additional testing will be required to extend the qualification scope. Engineers should review the original qualification documentation carefully against the new design conditions before assuming transferability.

What are the most common reasons a material qualification programme fails or is rejected by the inspection authority?

The most frequent causes of qualification rejection are incomplete traceability records, test results that fall outside code-required thresholds (particularly Charpy impact values at low temperatures), and welding procedure qualification data that does not adequately cover the thickness range or heat input conditions used in production. Gaps in chemical analysis documentation and failure to test at the actual minimum design metal temperature — rather than a conservative approximation — are also recurring issues. Engaging an experienced welding engineer and a qualified inspection body from the outset of the programme significantly reduces the risk of these failures.

How does post-weld heat treatment (PWHT) affect the material qualification process for advanced alloys?

For many advanced alloys — including high-strength low-alloy steels, duplex stainless steels, and nickel-based alloys — post-weld heat treatment has a direct effect on the final mechanical properties of the weld and heat-affected zone, meaning that PWHT parameters must be incorporated into the welding procedure qualification rather than treated as a separate manufacturing step. The qualification test welds must be subjected to the same PWHT cycle that will be applied in production, and the mechanical test results must be obtained from post-PWHT specimens. Any subsequent change to the PWHT temperature, hold time, or heating and cooling rates may invalidate the existing qualification and require requalification.

Is it possible to use a material that meets a foreign national standard (for example, a Japanese JIS or Chinese GB grade) in an ASME or PED-governed vessel?

Yes, but the pathway to approval requires additional steps compared to using a natively listed material. Under ASME, a material produced to a foreign standard can be used if it is demonstrated to be equivalent to an existing ASME specification or if a code case is approved for that specific grade. Under the PED, a material not covered by a harmonised European standard must go through the European Approval of Materials process. In both cases, the material producer’s quality system, testing protocols, and traceability practices must be shown to meet the requirements of the applicable code — simply having a conforming test certificate from the country of origin is not sufficient.

What should an engineer do if a material anomaly or non-conformance is discovered during fabrication of a newly qualified material?

Any non-conformance discovered during fabrication of a newly qualified material must be formally documented and assessed against the material specification and the applicable code before work continues. The engineer should raise a non-conformance report, determine whether the anomaly is within acceptable limits (for example, a minor dimensional deviation) or constitutes a genuine material defect, and involve the inspection authority if the defect affects structural integrity or code compliance. For novel materials with limited fabrication history, even seemingly minor anomalies warrant closer scrutiny, since there is less accumulated experience to draw on when judging whether a deviation is benign. Attempting to proceed without formal disposition is one of the most serious errors a fabrication team can make and can result in rejection of the completed vessel.