The Cathodic Disbondment Test (CD test) is carried out in the area of a coating holiday to determine the coating's susceptibility to disbondment due to cathodic corrosion protection. In addition, the test provides information about the quality of the tested coating, since the surface preparation before coating and the actual coating process itself have an effect on the coating's behavior regarding cathodic tunneling. The applicable standards are ISO 21809-1 for 3-layer polyolefin coatings and ISO 21809-2 for FBE coatings.

The lining of a pipe is subject to numerous loads in the course of its service life, such as erosion, temperature fluctuations, pressure or vibrations. The resistance of the lining material to these loads is regularly tested by determining its pressure resistance and tensile bending strength in accordance with DIN 1164. In addition, the lining components are tested and approved by external laboratories for their suitability for drinking water applications.

Offshore service in deep-sea regions involves enormous external pressures on the pipe used. Resistance to these pressures is tested in collapse tests. These tests determine a pipe's collapse resistance under real service conditions. When the external pressure is raised to the point of collapse, the test results provide information about the maximum loadability and failure behavior of the tested pipe.

The Crack Tip Opening Displacement (CTOD) test, according to standards such as BS 7448, ASTM E1290, ISO 12135, and ISO 15653, is a fracture mechanics method used to measure a material's resistance to crack growth, particularly for materials that exhibit plastic deformation before fracturing, such as steel in welded joints. It determines the toughness by measuring the crack tip opening at the onset of failure. A notched specimen, usually with a fatigue-precrack, is subjected to loading (often 3-point bending). A clip gauge measures the crack opening at the mouth, which is then related to the crack tip opening. The resulting CTOD value (d) indicates the material's ductility and resistance to crack propagation.

The drift test in accordance with API 5CT is used to verify the internal dimensional accuracy and straightness of casing and tubing pipes. For this purpose, a calibrated drift (cylindrical test mandrel) with a specified diameter is passed through the pipe over its entire length. The pipe is considered to have passed the test if the drift can be passed through freely and without obstruction.

The Battelle Drop Weight Tear Test serves as an acceptance criterion for individual plates and pipes and is usually carried out on specimens in accordance with DIN EN 10274 and/or API RP 5L3. During the test, pre-notched full-wall specimens are abruptly destroyed by a falling weight equipped with a fin. The percentage of shear fracture area is evaluated, which indirectly provides an indication of the crack arresting capacity of a pipe. In contrast to a Charpy Impact Test, in which a notched specimen is also abruptly broken, the focus of the BDWT-Test is not on crack initiation but on crack propagation. Additionally, the test can be carried out with instrumentation. In addition to the shear fracture ratio, the result provides values for the force and deflection of the specimen. This enables a clear differentiation between crack initiation and crack propagation energy and allows a clear correlation with the fracture surface.

The DSC test (Differential Scanning Calorimetry) is used in the testing of epoxy resins to analyze their curing behavior and thermal properties. The heat flow of the sample is measured during a defined temperature program, allowing conclusions to be drawn regarding the curing reaction, the degree of cure, and the glass transition temperature (Tg). The test is used for quality control and for optimizing curing processes of epoxy systems.

Fatigue tests are used to determine characteristic values for service life analysis. The material sample is subjected to cyclic loading in the range of pure tensile or compressive stress (threshold load test) or containing both tensile and compressive components (alternating load test). The load cycle number at which failure occurs under a specific load is evaluated. In technical terms, a material is considered to be fatigue-resistant under a certain load if the sample survives at least two million cycles without breaking. In certain applications, however, higher cycle numbers may also need to be tested. If different load horizons are tested, the cycles until sample failure can be represented in the form of stress-strain diagrams (Woehler diagrams).

Finite element analysis (FEA) can be used to predict the behaviour of an object on the basis of mathematical calculations. To do this, complex systems are broken down into smaller, simpler parts or ‘elements’, and descriptive differential equations are used to calculate and interpret the effect of an external change on each element individually, taking into account the interaction between the elements, with the aid of simulation software. The aim of finite element modelling is to replicate real systems and loads without the effort, time or risk, expense and cost of building and testing physical prototypes or systems. FEA can therefore be used, for example, to design new materials for steel pipes or to assess and optimise the behaviour of steel pipes under operating conditions.

Ring flattening tests are used for continuous monitoring of the quality of the base material and the weld seam. For this purpose, ring samples are taken from the manufactured pipe and compressed from one side. An assessment is made as to whether and how the areas with the highest tensile stress behave.

Fracture mechanic describes the behaviour of components with cracks or notches and determines whether crack propagation or fracture can be expected under operating conditions. In linear-elastic fracture mechanics (LEFM, for brittle materials), the material behaves in a linear-elastic manner up to deformation-free fracture. The result of such a test is the KIC value, the determination of which is described in ASTM E399. If, on the other hand, the material fails ductile, i.e. with plastic deformation around the crack tip, the concept of flow fracture mechanics (FBM) applies. In this case, the J-integral concept (energy in the crack tip region) is applied, or, in the case of crack tip expansion, the CTOD value is determined. Depending on the material and the standard, different specimen geometries are used. CT, SENT, SENB, or CTOD specimens can be tested within a temperature range of -196 °C up to +150 °C. In addition to determining material properties, component failure can be calculated using fracture mechanics methods for safety analysis, e.g. in accordance with BS 7910 or the FKM guideline. In this way, in addition to the critical crack size, a statement can also be made regarding the remaining service life.

The strain-based design properties of onshore pipe and the reeling properties of offshore pipe are determined in full-scale bending tests. On the LiSA (limit state analyzer) test stand, pipe can be subjected to 4-point bending tests until failure occurs, e.g. by buckling or cracking. This test can be carried out with and without internal pressure. By means of alternating bending cycles, the reeling process simulates the loads acting on offshore pipelines under real service conditions.

The guided bending test is a destructive testing method used to assess bending strength and bending resistance. For metallic materials, the bending test is carried out as a three-point bending test. The specimen is placed on two supports and is subjected to a central load using a bending punch and plastically deformed until a specific bending angle is reached. The results deliver characteristic values for the maximum bending stress, the fracture strength and the failure behaviour of the material. For example, the ductility and integrity of welds can be determined. The results reveal bonding defects, cracks or near-surface inclusions that lead to the failure of the specimen.

In conventional hardness testing, the resistance of a material surface to plastic deformation is determined using a standardised indenter. This is used to apply a specified force to the sample for a standardised period of time, after which the permanent indentation is measured. Since different indenters can be used (pyramid, ball, etc.), the test method must always be specified in addition to the hardness value. Hardness measurement can be used, for example, to compare steels, check the effectiveness of production processes such as heat treatment, assess unacceptable microstructural components such as martensite, or detect local microstructural differences.

The HIC test serves to determine a material's resistance to hydrogen-induced cracking. It provides information about the material's suitability for use with sour gas media. The tests are performed under standardized conditions to NACE TM0284, or under modified conditions adapted to the actual service environment as described in EFC 16 (EFC = European Federation of Corrosion). For the tests, modern, well-equipped laboratories accredited to ISO 17025 are available.

Component tests under internal pressure are carried out on line pipe and pressure vessel tubes. In the context of final inspection, these products are subjected to a pressure equal to 1.5 times the design operating pressure, to ensure that they can resist the service loads involved in the intended application. In addition, burst tests are carried out to determine their maximum loadability and failure mechanisms.

Light microscopic examinations are usually carried out to assess the microstructure. These determine, for example, the phases and phase proportions present or grain sizes. Furthermore, the possible presence of precipitates, segregation or oxides can be evaluated. A maximum magnification of 1000x is usually used. Due to the wavelength of light, the maximum resolution of the light microscope is limited to approximately 0.3 micrometres. If smaller structures are to be made visible, a scanning electron microscope (SEM) or transmission electron microscope can be used. These enable resolution down to atomic size.

The Charpy impact test (ISO 148-1) is a destructive test method for determining the toughness and brittle fracture behaviour of materials under impact loading. Toughness is a measure of the material's resistance to crack propagation. A notched sample is struck by a pendulum hammer from the side opposite the notch, and the absorbed energy is determined as the notch impact energy in joules. The samples are 55 x 10 x 10 mm in size, provided that the wall thickness of the manufactured pipe allows this.

A plastic coating must, above all, protect the pipe body against corrosion and therefore has to reliably resist external influences (pressure, impact, etc.). Peel resistance is an important quality feature of 3-layer polyolefin coatings, and indicates whether or not the 3-layer coating system consisting of a primer, an adhesive, and a polyolefin top layer has been applied correctly. The test is described in DIN 30670, DIN 30678 and ISO 21809-1. In addition, all our coatings have been approved for their respective application by external laboratories.

In-situ stress measurement involves the non-destructive or partially destructive determination of residual stresses in materials that exist without additional external loads. These stresses can result, for example, from forming or heat treatment processes and can lead to premature material failure or a reduction in material stress under external loads. The most commonly used methods are X-ray diffraction (XRD) analysis for near-surface areas, the borehole method with strain gauges (DMS) and, for pipes, the cutting method.

In the ring expansion test, a ring (150 mm high) cut from a pipe is expanded under internal pressure. The ring test press is designed so that the test rings are expanded radially only, and no restriction on longitudinal expansion occurs during the test. A uniaxial stress state exists in the test ring, which corresponds to the loading of the pipeline during operation. During the pressure increase, the circumferential strain ε of the test ring is measured using circumferential measuring chains, along with the fluid pressure p. From these, an integral determination can be made, such as the yield strength, across the entire ring circumference or the entire wall cross-section. In contrast, tensile tests on round specimens merely determine the material’s strength properties in a very localised manner in the transverse direction. Thus, the ring expansion test provides a more realistic description of the component’s strength properties than a tensile test. However, ring expansion tests are considerably more complex, difficult and expensive to conduct compared to tensile tests.

In the slow strain rate test (also called constant extension rate test CERT), a destructive testing method used in materials engineering, a tensile specimen is loaded at a very low, constant strain rate until fracture. This method can be used to investigate the sensitivity of pipe steels to stress corrosion cracking, hydrogen embrittlement or other environmentally induced cracking, for example. The test is usually carried out in an inert medium (e.g. nitrogen, air) and in the actual test medium (e.g. hydrogen gas). The influence of the medium is then assessed by comparing the characteristic values like tensile strength or elongation at break.

The SSC 4-point bending test is used to determine a steel's resistance to sulfide-stress-cracking. It provides information about a material's suitability for use with media containing sour gas and is described in ISO 15156. The tests can be carried out under standardized or modified conditions adapted to the application environment. The respective test conditions are described in NACE TM0177 and/or in NACE TM0316. For the tests, modern, well-equipped laboratories accredited to ISO 17025 are available.

The test is carried out in accordance with the relevant standards, such as DIN EN ISO 14284 and ASTM E415, using spectral analysis (optical emission spectrometry). In this process, the light emitted or absorbed by a sample is broken down into its spectral components.

In steel, ageing leads to embrittlement and, consequently, a reduction in plastic deformation capacity once the yield strength is exceeded. At the same time, the yield strength may increase. The cause of embrittlement are submicroscopic precipitations, e.g. due to the diffusion of carbon atoms to dislocations, which increases their activation energy and aggravates their movement on the slip planes of the crystallites. 
Evidence of possible ageing can only be provided by destructive testing methods (tensile test, notched impact test). A distinction is made between:

a. natural ageing; this occurs after cold forming and subsequent storage (from a few hundred hours to months or years) at room temperature
b. artificial ageing; this occurs after cold forming and subsequent brief heating (minutes to hours) to 100 to 300 °C.

The tensile test is a mechanical material testing procedure used to characterise the strength and deformation behaviour of the material. During tensile loading at low strain rates, the force and change in length of the specimen are measured until it breaks. In the case of steels, this is usually used to determine the yield strength, tensile strength and elongation at break. These characteristic values form the basis for the dimensioning of pipelines, for example, and are used in quality control to assess the uniformity of pipe production.

The through-thickness tensile test (Z‑direction) is used to determine the mechanical deformability perpendicular to the rolling plane. It is applied to assess the susceptibility to lamellar tearing, particularly in highly restrained welded structures. The test is carried out by subjecting a specimen taken from the plate thickness to tensile loading until fracture; the decisive parameter is the percentage reduction of area at fracture. The test is specified in EN 10164 and forms the basis for Z‑qualities such as Z25 or Z35.

The welding procedure qualification serves to determine whether a steel material can be welded without cracking and with the required mechanical properties of the weld under defined manufacturing conditions. In the case of steel pipes, weldability tests are used to demonstrate that grith welds during pipe laying can fulfil the requirements. All parameters used are documented during the welding test. These include the welding process, the size, type and classification of the welding filler material, the type and thickness of the welded base material, type, polarity and level of welding current, welding voltage, welding speed, welding position, type and dimensions of the joint design, preheating temperature, interpass temperature, heat treatment details after welding, etc. The weld seam produced is inspected using both non-destructive methods such as X-ray, ultrasonic or magnetic particle testing, and destructive methods such as microstructure examinations, hardness measurements, tensile tests, and others. The results are summarized within a report (WPQR). In the case of a successful qualification, the preliminary welding parameters are transferred to a final welding procedure specification (WPS).

The purpose of this test is to determine whether corrosion penetrates the coating under cathodic polarisation of the steel substrate; in other words, to verify the correct execution of surface preparation and the application of the epoxy primer, as well as the suitability of the coating system for use in cathodic corrosion protection. The test is described in DIN 30670, DIN 30678 and ISO 21809-1. 

The aim of the test is to detect defects in the coating using a high-voltage test. Defects, such as pores, cracks and/or other weaknesses, are indicated visually and/or acoustically by a spark that jumps between the steel and the test probe. The test is described in DIN 30670, DIN 30678 and ISO 21809-1.

In addition to the standard tests required by the relevant standards during pipe manufacture, MGR has carried out in collaboration with Salzgitter Mannesmann Forschung several tests to assess the integrity of pipelines. Among other things, these tests can examine the collapse behaviour of pipes under external pressure (offshore applications) and determine the maximum load-bearing capacity and failure behaviour of the pipes.

In addition to the standard tests required by standards during pipe manufacturing, further tests can be carried out to assess the quality of spiral-welded pipes. For example, the Crack Tip Opening Displacement (CTOD) test can be performed in accordance with standards such as BS 7448, ASTM E1290, ISO 12135 and ISO 15653. This is a fracture mechanics method for measuring a material’s resistance to crack propagation. It is used in particular for materials that undergo plastic deformation prior to fracture, such as steel in welded joints. The CTOD value (d) resulting from the test indicates the ductility and the material’s resistance to crack propagation.

During final inspection, all pipes undergo a dimensional check. The inspection verifies whether the requirements set out in the specifications regarding pipe geometry (length, diameter, ovality, wall thickness, etc.) and weld formation (weld bevel, edge misalignment, weld geometry, etc.), as well as tolerances for surface defects, have been maintained.

The drop weight test is performed in accordance with DIN EN 10274 and API 5L3 on samples. A defined weight is dropped from a defined height onto a notched sample. The appearance of the fracture surfaces is then assessed. The proportions of the deformation fracture surface and brittle fracture surface of the metal sample are evaluated visually. 

Thermal analysis (differential scanning calorimetry, DSC) is used to characterise the uncured epoxy resin (powder, single-component liquid or two-component liquid) and the cured coating layer. This involves measuring the heat flow of the sample during a defined temperature programme, which allows conclusions to be drawn regarding the curing reaction, the degree of cure and the glass transition temperature (Tg). The test is used for quality control and to optimise the curing processes of epoxy systems.

Elongation at break is tested in accordance with DIN EN ISO 527-1 to DIN EN ISO 527-3. The test provides information on how well a plastic can withstand tensile loads.

In addition to the standard tests required by the relevant standards during pipe manufacture, MGR has carried out several investigations into the assessment of pipe integrity in collaboration with Salzgitter Mannesmann Forschung. Among other things, fatigue tests can also be carried out on pipes. In these tests, pipe material samples are subjected to cyclic loading, comprising peak load tests in the tensile or compressive range as well as alternating load tests involving both tensile and compressive components. These tests enable the determination of parameters for service life analysis.

In addition to the standard tests required by the relevant standards in pipe manufacturing, MGR has carried out several projects in collaboration with Salzgitter Mannesmann Forschung to simulate processes and material behaviour in tube manufacturing. Among other things, the following topics were addressed:

• Residual stress state in the strip after decoiling and straightening of hot-rolled strip
• Anisotropic behaviour in components of spiral-welded pipes
• Simulation of stress states “LiSA”
• Investigation of the effects of specimen straightening on material properties
• Deformation and stress analysis of the roller support in the spiral tube forming line

The results obtained were applied in various projects, for example in the design of tube forming lines or in the preparation of specimens for mechanical testing.

The test is designed to assess the flexibility of three-layer polyolefin coatings on pipes. It is carried out in accordance with ISO 21809-1 and is intended to ensure that the coating does not crack or peel off when bent or deformed, thereby losing its protective function.

Hardness testing is a depth-differential method in which the material’s resistance to permanent deformation is measured. To achieve this, an indenter is pressed into the material with a specific test force. The resulting indentation depth or the permanent impression left by the indenter is then measured, and the hardness value of the metal is calculated. Hardness testing can be used, for example, to assess microstructure and properties of the base material, heat-affected zone and weld metal, or to detect local variations in microstructure.

The HIC test serves to determine a material's resistance to hydrogen-induced cracking. It provides information about the material's suitability for use with sour gas media. The tests are performed under standardized conditions to NACE TM0284, or under modified conditions adapted to the actual service environment as described in EFC 16 (EFC = European Federation of Corrosion). For the tests, modern, well-equipped laboratories accredited to ISO 17025 are available.

The hot tensile test in accordance with DIN EN ISO 6892-2 is a mechanical testing method used to characterise the strength and deformation behaviour of a material at elevated temperatures. This test is typically used to determine, in particular, the yield strength, tensile strength and elongation at break. These parameters form, amongst other things, the basis for assessing the integrity of pipes used for the transport of district heating or hot media.

This test is designed to assess the resistance of factory-applied three-layer polyolefin coatings on pipes to loss of adhesion to the steel substrate in a humid environment. The test may be carried out on the coated pipe without cutting samples. The test is described in DIN 30670, DIN 30678 and ISO 21809-1.

This test determines the depth of penetration of a punch into the coating under specified temperature and load conditions. The test provides information on the coating’s resistance to mechanical stress and is described in DIN 30670, DIN 30678 and ISO 21809-1.

During final inspection, all pipes are visually inspected inside and outside. A check is carried out to ensure that any defects (relating to the surface, weld seam or pipe ends) identified during the preliminary inspection (internally after pipe forming and externally after welding), marked and recorded in the MVS, have been rectified in accordance with best practice. Any rectifications are marked and instructions are provided for further processing.

In macrographic examination (macro-etching), a destructive testing method used to examine welds, the weld structure is made visible in a cross-section. This method allows the weld quality, weld structure, weld geometry and any macro-defects to be assessed.

Determining the melt flow rate of plastic outer casings provides information about the material’s flow behaviour under defined conditions and can therefore help to assess its processability in the molten state.

Optical microscopy can be used to assess the microstructure of the base material, spiral seam or heat-affected zone. In our metallographic laboratory, we can determine the phases present, their proportions and grain sizes. Furthermore, the purity of the raw material can be determined and the possible presence of precipitates, segregation or oxides assessed. If smaller structures are to be visualised, a scanning electron microscope (SEM) or transmission electron microscope can be used. These enable resolution down to atomic scale.

The Charpy impact test (ISO 148-1) is a destructive testing method used to determine the toughness and brittle fracture behaviour of materials under impact loading. Toughness is a measure of the material’s resistance to crack propagation. In this test, a notched specimen is shattered by a pendulum hammer striking it from the side opposite the notch, with the absorbed energy being determined as the impact energy in joules. 

The peel strength test is used to verify the correct application of the combination of epoxy primer, PE adhesive and polyethylene top coat. In this test, the force required to peel the coating away from the metal substrate (steel) at a constant tensile speed must be measured. The test is described in DIN 30670, DIN 30678 and ISO 21809-1. 

The test is carried out in accordance with applicable standards (DIN EN ISO 14284, ASTM E415) using spectral analysis (optical emission spectrometry). This consists of  determining the chemical composition of samples taken from the pipes and comparing it with the results of the melt analysis.

In addition to the standard tests required by regulations during pipe manufacture, MGR has carried out several investigations into the assessment of pipe integrity in collaboration with Salzgitter Mannesmann Forschung. Among other things, residual stress measurements can be performed using non-destructive or semi-destructive methods. The most commonly used methods are X-ray diffraction (XRD) for near-surface areas, the borehole method using strain gauges (SG), and, for pipes, the cut-open method.

In the slow strain rate test (also called constant extension rate test CERT), a destructive testing method used in materials engineering, a tensile specimen is loaded at a very low, constant strain rate until fracture. This method can be used to investigate the sensitivity of pipe steels to stress corrosion cracking, hydrogen embrittlement or other environmentally induced cracking, for example. The test is usually carried out in an inert medium (e.g. nitrogen, air) and in the actual test medium (e.g. hydrogen gas). The influence of the medium is then assessed by comparing the characteristic values like tensile strength or elongation at break.

The SSC 4-point bending test is used to determine a steel's resistance to hydrogen-induced stress cracking. It provides information about a material's suitability for use with media containing sour gas and is described in ASTM G39. The tests can be carried out under standardized or modified conditions adapted to the application environment. The respective test conditions are described in NACE TM0177 and/or in EFC 16. For the tests, modern, well-equipped laboratories accredited to ISO 17025 are available.

The test is carried out in accordance with the relevant standards, such as DIN EN ISO 14284 and ASTM E415, using spectral analysis (optical emission spectrometry). In this process, the light emitted or absorbed by a sample is broken down into its spectral components.

Additionally to the normative standard testing of pipe production MGR has carried out several investigations related to the assessment of pipelines integrity. Among other things the ageing of steel due to several causes (natural, artifical) can be investigated and determinated by means of destructive testing.

The tensile test is used to characterise the strength and deformation behaviour of the manufactured pipes. It is primarily used to determine the yield strength, tensile strength and elongation at break. These parameters are used, amongst other things, for assessing pipeline integrity.

Ultrasonic testing of the raw material takes place at the inlet of the tube forming line using an automated system with up to 20 oscillating probes. The number of probes depends on the strip width and the requirements of the applicable specifications. The raw material (coil) is tested and assessed in accordance with DIN EN ISO 10893-9 using an ultrasonic pulse-echo technique to detect double layers, with the sound beam directed perpendicular to the strip/sheet surface. 

Ultrasonic testing of the weld is carried out using an full automated system. The pulse-echo method is used to test for longitudinal and transverse defects. For this purpose, up to 14 probes are positioned at specific distances from the weld seam or directly on the weld seams. The aim is to detect internal defects such as cracks, lack of fusion or slag inclusions and to assess them in accordance with DIN EN ISO 10893-11.

This test is designed to assess the durability of factory-applied three-layer polyolefin coatings on pipes against loss of adhesion to the steel substrate in a humid environment. The test may be carried out on the coated pipe without cutting samples. The hot water immersion test is described in DIN EN ISO 21809-1.

The weldability of the pipes during the pipe-laying process can be verified in advance at the Salzgitter Mannesmann Forschung laboratory for specific welding processes and filler materials. To this end, a exhaustive welding procedure qualification, including the associated non-destructive and destructive tests, is carried out and documented. The welding parameters used and the results achieved are recorded in  an exemplary welding procedures.

The X-ray inspection, carried out using a digital radiography system, comprises an X-ray tube, a detector (DDA) and analysis software. The procedure involves inspecting and assessing the weld seam, repair areas and the uninspected weld seam at the pipe ends in accordance with DIN EN ISO 10893-7.

Chamfer measurements are performed on finished tubes. The measurement can be performed tactilely or optically. The test is performed to ensure that the geometric requirements for the chamfer are met. Characteristic values that are determined include chamfer length, chamfer angle, etc.

The aim is to check the inner diameter tolerance, straightness and to ensure that the tube is free to pass through. To do this, a standardized mandrel is fed through the entire length of the tube.

The inspection for punctiform or sliver surface inhomogeneities on the outer surface is carried out using eddy currents. The tubes are fed through a fully automated inspection system. Inhomogeneities that have the same interaction volume as the reference reflector are classified as defects and sorted out. Depending on the eddy current testing technique, through holes or notches are used as reference defects. Due to physical limitations, the test is carried out in combination with ultrasonic testing, depending on customer requirements. Eddy current testing is also used as a leak test.

Flattening tests are used for continuous monitoring of the quality of the base material and the weld seam. For this purpose, ring samples are taken from the manufactured pipe and compressed from one side. An assessment is made as to whether and how the areas with the highest tensile stress behave.

Geometric measurements are performed on long tubes as well as short lengths. The measurements can be performed tactilely or optically, using manual measuring instruments or automated systems. The following properties are checked and compared with customer requirements: straightness or roundness, length, axial runout, and, of course, outer and inner diameter as well as wall thickness.

In conventional hardness testing, the resistance of a material surface to plastic deformation is determined using a standardised indenter. This is used to apply a specified force to the sample for a standardised period of time, after which the permanent indentation is measured. Since different indenters can be used (pyramid, ball, etc.), the test method must always be specified in addition to the hardness value. Hardness measurement can be used, for example, to compare steels, check the effectiveness of production processes such as heat treatment, assess unacceptable microstructural components such as martensite, or detect local microstructural differences.

The tensile test, which in this case is performed at elevated temperatures, is a mechanical material testing procedure used to characterize the strength and deformation behavior of the material. It is used to evaluate the high-temperature strength of metals using a tensile testing machine and a furnace. In the case of steels, the yield strength, tensile strength, and elongation at break are usually determined. These characteristic values serve as basis for the dimensioning, for example, and are used in quality control to assess the uniformity of tube production. The test is described in DIN EN ISO 6892-2.

The tubes are tested in accordance with DIN 50104 or other agreed standards (e.g., ASTM, API 5L). The tubes to be tested are subjected to water pressure (max. 750 bar).

Material mix-up checks are carried out to ensure that no other steel grades are delivered to the customer. The measurements can be carried out using a spectrometer or magnetic induction. The entire process can be carried out manually or fully automatically. Ensuring steel quality is important because product properties such as tensile strength, weldability, etc. depend on it.

Light microscopic examinations are usually carried out to assess the microstructure. These determine, for example, the phases and phase proportions present or grain sizes. Furthermore, the possible presence of precipitates, segregation or oxides can be evaluated. A maximum magnification of 1000x is usually used. Due to the wavelength of light, the maximum resolution of the light microscope is limited to approximately 0.3 micrometres. If smaller structures are to be made visible, a scanning electron microscope (SEM) or transmission electron microscope can be used. These enable resolution down to atomic size. In addition, it is possible to determine the degree of purity and the depth of decarburization.

The Charpy impact test (ISO 148-1) is a destructive test method for determining the toughness and brittle fracture behaviour of materials under impact loading. Toughness is a measure of the material's resistance to crack propagation. A notched sample is struck by a pendulum hammer from the side opposite the notch, and the absorbed energy is determined as the notch impact energy in joules. The specimen is 55 x 10 x 10 mm in size, provided that the manufactured tube size allows this - for smaller tubes, under-size samples are taken and results are converted in accordance with the corresponding standards.

Simulated heat treatment in a laboratory furnace up to 1,200°C, followed by a tensile test, hot tensile test, and/or Charpy impact testing.

The ring specimens (specimen length 10–16 mm) are expanded until they break and then checked for macroscopically visible surface defects. The deformability is assessed on the basis of the fracture and the fracture surfaces. The test is described in DIN EN ISO 8495.

Roughness measurements are performed to determine characteristic values for the surface structure. The measurement can be tactile or optical. These characteristic values influence functional properties such as friction, adhesion, wear, etc.

The test is carried out in accordance with the relevant standards, such as DIN EN ISO 14284 and ASTM E415, using spectral analysis (optical emission spectrometry). In this process, the light emitted or absorbed by a sample is broken down into its spectral components.

The step turning test is a test method for determining macroscopic non-metallic inclusions. Three different diameters are created on a sample by turning. The inclusions found in the three diameters are marked and then counted. The test is described in ISO 3763.

The tensile test is a mechanical material testing procedure used to characterise the strength and deformation behaviour of the material. During tensile loading at low strain rates, the force and change in length of the specimen are measured until it breaks. In the case of steels, this is usually used to determine the yield strength, tensile strength and elongation at break. These characteristic values form the basis for the dimensioning of pipelines, for example, and are used in quality control to assess the uniformity of pipe production.

Ultrasound is used to check for inhomogeneities on the inner and outer walls. The tubes are fed through a fully automated testing system and compared with a reference reflector. Inhomogeneities that produce the same or a stronger signal than the reference reflector are detected as defects and rejected. The reference reflector used here is a notch. Due to physical limitations, the test is performed in combination with eddy current testing, depending on customer requirements.

The tubes must be inspected visually to ensure they meet the specified requirements.