Internal roughness testing service

Internal Roughness Testing Service – Accredited ISO/IEC 17025 Surface Characterization and Flow Performance Assessment for the Croatian Market

Internal roughness is a critical surface parameter that significantly influences the flow characteristics, pressure drop, heat transfer efficiency, corrosion susceptibility, and fouling behavior of pipes, tubes, ducts, and other fluid‑handling components. In industries such as oil and gas, chemical processing, power generation, water treatment, pharmaceuticals, food and beverage, and hydraulic systems, the accurate characterization of internal surface topography is essential for optimizing system design, predicting service life, and ensuring operational efficiency and safety. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Carinska uprava enforce strict quality, energy efficiency, and performance standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of internal roughness is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive internal roughness testing service, applying standardized methods such as ISO 4287, ASME B46.1, ISO 13565, ASTM D7127, VDA 2005, and HRN EN ISO 4287 to measure surface roughness parameters (Ra, Rz, Rq, Rmax, and Rsk) using contact and non‑contact profilometry techniques, and to correlate roughness with fluid flow performance and corrosion resistance. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Internal Surfaces and Components We Regularly Test

Our laboratory receives a wide variety of components and internal surfaces for roughness testing. Typical samples include:

• Pipes, tubes, and pipelines – seamless and welded, metallic and non‑metallic, for oil, gas, water, and chemical transport.
• Heat exchanger tubes and condensers – for power generation and chemical processing.
• Hydraulic and pneumatic cylinders – for industrial machinery and automotive applications.
• Valve bodies and fittings – for fluid control and regulation.
• Pump casings and impellers – for centrifugal and positive displacement pumps.
• Medical and pharmaceutical tubing – for drug delivery and diagnostic systems.
• Food and beverage processing equipment – for hygienic and sanitary applications.
• Prototype and new component designs – submitted by manufacturers for validation of surface quality before series production.
• Field‑retrieved components – for failure analysis and remaining life assessment.

Contact Profilometry – Stylus‑Based Roughness Measurement

Contact profilometry uses a diamond stylus that traverses the internal surface of the component, measuring the vertical displacement of the stylus as it moves across the surface. This method is the most widely used and standardized technique for measuring surface roughness. Our procedures follow international standards and the requirements of the Croatian industrial, automotive, and energy sectors.

• Stylus profilometry measurement (ISO 4287 / ASME B46.1 / HRN EN ISO 4287 / NTC 5600 – for general surface roughness) – we use a calibrated contact profilometer with a diamond stylus (tip radius 2 μm to 5 μm) to measure the surface roughness profile along a specified evaluation length (typically 5 mm to 20 mm) on the internal surface of the component. The stylus traverses the surface at a constant speed (typically 0.5 mm/s to 1 mm/s), and the vertical displacement is recorded. We calculate the standard roughness parameters: Ra (arithmetic mean deviation), Rz (average maximum height), Rq (root mean square deviation), Rmax (maximum peak‑to‑valley height), and Rsk (skewness). We report the roughness profile, the measured parameters, the evaluation length, and the measurement uncertainty.
• Roughness measurement on curved surfaces (NTC 5601 – for pipes and tubes) – for curved internal surfaces (e.g., pipes), we use a special probe or a test fixture that allows the stylus to traverse the surface in a controlled manner. We apply a correction factor for the curvature effect and report the corrected roughness values. We report the roughness values and the correction factor.
• Roughness measurement on small‑diameter tubes (NTC 5602 – for confined spaces) – for small‑diameter tubes (< 10 mm), we use a miniature stylus probe with a smaller tip radius (1 μm) and a reduced gauge length. We report the roughness values and the measurement limitations.
• Roughness measurement at different orientations (NTC 5603 – for the directional analysis) – we perform roughness measurements in multiple directions (e.g., longitudinal and transverse) to evaluate the anisotropy of the surface texture. We report the roughness values for each direction and the anisotropy ratio.
• Roughness measurement at different temperatures (NTC 5604 – for the thermal effect) – we perform the roughness measurement at elevated temperatures (e.g., 40 °C, 60 °C) using a heated test fixture, to evaluate the effect of temperature on the surface topography. We report the roughness values at each temperature.

Optical Profilometry – Non‑Contact Roughness Measurement

Optical profilometry uses white light interferometry, confocal microscopy, or laser triangulation to measure the surface topography without physical contact. This method is ideal for soft, delicate, or highly reflective surfaces, and it provides a high‑resolution 3‑D representation of the surface. Our procedures follow international standards and the requirements of the Croatian high‑precision and medical device industries.

• White light interferometry (WLI) – ISO 25178 / NTC 5610 – for high‑resolution 3‑D surface measurement – we use a white light interferometer to scan the internal surface of the component and generate a high‑resolution 3‑D topographic map. We measure the 2‑D parameters (Ra, Rz, Rq) and the 3‑D parameters (Sa, Sz, Sq, Ssk, and Sku). We report the 3‑D surface map, the measured parameters, and the areal material ratio.
• Confocal microscopy (NTC 5611 – for the high‑magnification surface imaging) – we use a confocal microscope to capture high‑magnification images of the internal surface, and we generate a 3‑D surface reconstruction from the stack of images. The roughness parameters and the surface texture are reported. We report the 3‑D surface images and the roughness parameters.
• Laser profilometry (NTC 5612 – for the large‑area scanning) – we use a laser triangulation profilometer to scan the internal surface over a large area (up to several centimeters) and to measure the surface profile. We report the 2‑D and 3‑D roughness parameters and the surface map.
• Comparative measurement of different optical methods (NTC 5613 – for the method validation) – we perform roughness measurements using multiple optical methods (WLI, confocal, and laser) and compare the results to identify the most appropriate method for the specific material and surface texture. We report the comparison and the method recommendation.
• Measurement of transparent and reflective surfaces (NTC 5614 – for the special materials) – for transparent (e.g., glass, polymer) or highly reflective (e.g., polished metal) surfaces, we use an optical profilometer with a specific light source (e.g., a blue light or a polarized light) to reduce the reflection and to obtain a reliable measurement. We report the roughness values and the measurement conditions.

Roughness Parameters and Interpretation – Quantifying the Surface Texture

The surface roughness parameters provide a quantitative description of the surface texture. Our tests measure a comprehensive set of parameters, and we interpret the results in the context of the specific application (e.g., flow performance, corrosion resistance, or sealability).

• Amplitude parameters (Ra, Rz, Rq, Rmax – NTC 5620 – for the height characterization) – we measure the amplitude parameters (Ra, Rz, Rq, and Rmax) from the roughness profile. The amplitude parameters describe the vertical extent of the surface irregularities. We report the amplitude parameters and the interpretation.
• Hybrid parameters (Rsk, Rku – NTC 5621 – for the shape characterization) – we measure the skewness (Rsk) and the kurtosis (Rku) of the roughness profile. The skewness describes the asymmetry of the profile, and the kurtosis describes the peakedness. These parameters are used to assess the load‑bearing capacity and the wear resistance of the surface. We report the Rsk and Rku values and the interpretation.
• Spacing parameters (RSm, RΔq – NTC 5622 – for the lateral characterization) – we measure the mean spacing of the profile irregularities (RSm) and the root mean square slope (RΔq). These parameters are used to assess the density of the surface features and the surface drainage properties. We report the RSm and RΔq values and the interpretation.
• Material ratio curve (Abbott‑Firestone curve – NTC 5623 – for the bearing area analysis) – we generate the material ratio curve (the Abbott‑Firestone curve) from the roughness profile. The curve provides the bearing area as a function of the depth. The material ratio is correlated with the sealing performance and the wear resistance. We report the material ratio curve and the Rpk, Rk, and Rvk parameters.
• Correlation of roughness parameters with the application (NTC 5624 – for the performance‑based assessment) – we correlate the measured roughness parameters with the specific application (e.g., the pressure drop in a pipe, the heat transfer in a heat exchanger, or the leakage in a seal). The correlation is based on the empirical models (e.g., the Moody chart, the Nusselt correlation) or on the manufacturer's specifications. We report the correlation and the application‑specific recommendations.

Corrosion and Fouling Susceptibility – Evaluating the Effect of Roughness on Durability

The internal roughness of a component can significantly affect its resistance to corrosion, erosion, and fouling. Our tests evaluate the susceptibility of the surface to these degradation mechanisms and provide data for the selection of the optimal surface finish for the intended service environment.

• Corrosion susceptibility assessment (NTC 5630 – for the pitting and crevice corrosion) – we correlate the measured roughness (especially the Rz and Rmax values) with the susceptibility to pitting and crevice corrosion. A rougher surface provides more sites for the initiation of localized corrosion. We report the corrosion susceptibility rating and the recommended surface finish.
• Erosion resistance assessment (NTC 5631 – for the particle erosion) – we correlate the roughness with the erosion resistance (especially the Rsk and RSm values). A surface with a positive skewness (peaks) is more susceptible to erosion. We report the erosion resistance rating and the recommended surface finish.
• Fouling and deposit formation assessment (NTC 5632 – for the scaling and bio‑fouling) – we correlate the roughness (especially the Ra and Rz values) with the tendency for deposit formation (fouling). A rougher surface provides more sites for the adhesion of deposits. We report the fouling susceptibility rating and the recommended cleaning intervals.
• Wear and abrasion resistance assessment (NTC 5633 – for the mechanical wear) – we correlate the roughness (especially the Rpk and Rk values) with the wear resistance. A surface with a low bearing area (low Rpk) is more wear‑resistant. We report the wear resistance rating and the recommended surface treatment.
• Corrosion and roughness correlation (NTC 5634 – for the life prediction) – we use the measured roughness and the material's corrosion rate to predict the service life of the component. The life prediction is based on the NACE or the API corrosion models. We report the predicted service life and the recommended inspection intervals.

Environmental and Aging Effects on Roughness – Evaluating the Long‑Term Stability

The internal roughness of a component can change over time due to corrosion, erosion, wear, and deposit formation. Our environmental and aging tests evaluate the long‑term stability of the surface finish, ensuring the reliability of the component over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Corrosion and erosion exposure test (NTC 5640 – for the simulated service exposure) – we expose the component to a corrosive or erosive environment (e.g., salt spray, acidic solution, or abrasive slurry) for a specified duration (e.g., 7, 14, or 28 days) and then re‑measure the internal roughness. The change in the roughness (in %) is reported. We report the roughness after exposure and the change.
• Thermal aging effect on roughness (NTC 5641 – for the heat‑aged components) – we age the component in an oven at a specified temperature (e.g., 70 °C, 100 °C) for a specified duration (e.g., 7, 14, or 28 days) and then re‑measure the roughness. The change in the roughness and the formation of any oxide scale are reported. We report the roughness after aging and the oxide condition.
• Water immersion and moisture effect (NTC 5642 – for the moisture‑exposed components) – we immerse the component in water (or a process fluid) for a specified duration (e.g., 7 days) and then re‑measure the roughness. The change in the roughness and the presence of any deposits are reported. We report the roughness after immersion and the deposit condition.
• Chemical exposure effect (NTC 5643 – for the chemically exposed components) – we immerse the component in various chemicals (e.g., mineral oil, 10 % HCl, 10 % NaOH, or a solvent) for a specified duration (e.g., 7 days) and then re‑measure the roughness. The change in the roughness and the surface condition (e.g., etching, pitting) are reported. We report the roughness after chemical exposure and the surface condition.
• Wear and abrasion effect (NTC 5644 – for the mechanical wear) – we subject the internal surface to a specified number of wear cycles (e.g., by passing an abrasive fluid through the component) and then re‑measure the roughness. The change in the roughness and the wear pattern are reported. We report the roughness after wear and the wear pattern.

Complementary Tests – Dimensional Inspection, Hardness, and Material Verification for Roughness Correlation

To provide a comprehensive assessment of the component's quality and to understand the factors that influence the surface roughness, we perform complementary tests, including dimensional inspection, hardness testing, and material verification.

• Dimensional inspection (NTC 5650 – for the diameter, wall thickness, and geometry) – we measure the internal diameter, the wall thickness, and the geometry (the ovality, the straightness) of the component using calibrated instruments (e.g., micrometers, bore gauges, and CMM). The dimensions are correlated with the roughness. We report the dimensions and the geometry.
• Hardness testing (ASTM E18 / NTC 5651 – Rockwell, Brinell, or Vickers) – we measure the hardness of the component material (HRC, HRB, HB, or HV). The hardness is correlated with the wear resistance and the ability to maintain a smooth surface finish. We report the hardness and the correlation.
• Material identification (FTIR, XRF – NTC 5652 – for the material verification) – we use Fourier‑transform infrared spectroscopy (FTIR) and X‑ray fluorescence (XRF) to identify the chemical composition of the component material and to verify that it matches the specified grade. The material type is correlated with the roughness and the corrosion resistance. We report the material identification and the compliance.
• Metallographic examination (ASTM E3 / NTC 5653 – for the grain size and the microstructure) – we examine the microstructure of the component material (the grain size, the phase distribution, and the inclusion content) using optical microscopy and SEM. The microstructure is correlated with the surface finish and the wear resistance. We report the grain size, the phase distribution, and the inclusion rating.
• Surface defect analysis (NTC 5654 – for the detection of defects) – we use a borescope or a video inspection system to inspect the internal surface for defects (e.g., cracks, pits, laps, or gouges) that could affect the roughness and the performance. We report the location, the type, and the severity of any defects.

Test Report and Recognition in the Croatian Industrial, Energy, and Manufacturing Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (profilometers, optical profilers, CMMs, and measuring instruments) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the test sample (component type, material, dimensions, and manufacturer).
• Detailed description of the test methods applied (ISO/ASME/ASTM/VDA/HRN EN/NTC standards, test conditions, and measurement parameters).
• Numerical results: roughness parameters (Ra, Rz, Rq, Rmax, Rsk, RSm, Rpk, Rk, Rvk), 3‑D parameters (Sa, Sz, Sq), dimensional data (diameter, wall thickness), hardness (HRC/HV), and property retention after environmental exposure (%).
• Graphical data: roughness profiles, 3‑D surface maps, material ratio curves, and roughness vs. application correlation plots.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ISO 4287, ASME B46.1, ISO 13565, HRN EN ISO 4287, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs of the internal surface (from the borescope inspection) and the profilometry traces.
• Recommendations for surface finish optimization, material selection, and quality control measures to achieve the required roughness and performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for industrial and energy compliance, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of pipes, tubes, and other fluid‑handling components. Additionally, we offer consulting services for the selection of optimal surface finishes, the design of corrosion‑resistant and erosion‑resistant systems, and the implementation of quality control programs for internal surface quality, contributing to the safety, efficiency, and reliability of fluid‑handling systems in the diverse and growing Croatian market, from the oil and gas pipelines to the pharmaceutical and food processing facilities.