Study and testing of inner wall roughness

Study and Testing of Inner Wall Roughness – Accredited ISO/IEC 17025 Surface Characterization Services for the Colombian Market

The inner wall roughness of pipes, tubes, ducts, and fluid-handling components is a critical parameter that directly influences flow resistance, pressure drop, energy efficiency, heat transfer, corrosion susceptibility, and the accumulation of deposits or biofilms. In industries such as oil and gas, chemical processing, power generation, food and beverage, pharmaceuticals, and water treatment, the accurate characterization of internal surface topography is essential for optimizing system design, predicting service life, and ensuring operational reliability. In the Colombian market, where the Agencia Nacional de Hidrocarburos (ANH), the Ministerio de Minas y Energía (MinMinas), the Superintendencia de Industria y Comercio (SIC), and the Dirección de Impuestos y Aduanas Nacionales (DIAN) enforce strict quality and efficiency standards for industrial systems, the rigorous evaluation of inner wall roughness is fundamental for product certification, quality control in manufacturing, validation of cleaning and maintenance procedures, and import-export processes. Our laboratory offers a comprehensive service for the study and testing of inner wall roughness, applying standardized contact and non-contact profilometry methods to measure roughness parameters such as Ra, Rz, Rq, and Rmax, as well as to assess corrosion, wear, and deposit formation on internal surfaces. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Colombian authorities, making them essential for design validation, quality assurance, and regulatory compliance in the Colombian industrial and infrastructure sectors.

Test Samples and Components We Regularly Examine

Our laboratory receives a wide variety of components and systems for inner wall roughness testing. Typical samples include:

• Steel pipes and tubes – seamless and welded, of various diameters (from ½″ to 48″) and wall thicknesses, used in oil, gas, and water transportation.
• Stainless steel and alloy pipes – for chemical, pharmaceutical, and food processing applications, requiring smooth internal surfaces for hygiene and corrosion resistance.
• Copper, aluminum, and plastic pipes – for HVAC, refrigeration, and plumbing systems.
• Flexible hoses and rubber liners – for assessing surface quality after extrusion or molding.
• Hydraulic cylinders and pneumatic tubing – where surface roughness affects seal performance and friction.
• Heat exchanger tubes and boiler tubes – where roughness impacts heat transfer efficiency and fouling.
• Piping systems after cleaning (pigging, chemical cleaning) – to evaluate cleaning effectiveness and surface quality.
• Prototype and new pipe designs – submitted by manufacturers for validation of internal surface quality before series production.
• Used or aged pipe sections – extracted from field installations, for analysis of wear, corrosion, and deposit build-up.

Profilometry for Inner Wall Roughness – Contact and Non-Contact Methods

We employ both contact and non-contact profilometry techniques to measure inner wall roughness. The choice of method depends on the pipe diameter, access, material, and the required measurement resolution. Our methods follow international standards and the requirements of the Colombian oil, gas, and manufacturing sectors.

• Contact profilometry with a stylus (ISO 4287 / ASME B46.1 / NTC 5800) – for pipes with a diameter of at least 50 mm (allowing access for the stylus probe), we use a contact profilometer with a diamond stylus (tip radius 2‑5 μm). The stylus traverses the inner surface along a specified length (typically 5 to 20 mm), and the vertical displacement is recorded to generate a roughness profile. We measure the standard roughness parameters: Ra (arithmetic mean deviation), Rz (average maximum height of the profile), Rq (root mean square deviation), and Rmax (maximum peak-to-valley height). We report the roughness profile, the measured parameters, and the measurement uncertainty.
• Non-contact optical profilometry (ISO 25178 / NTC 5801 – white light interferometry or confocal microscopy) – for small-diameter pipes or for applications requiring a high-resolution 3D surface map, we use a non-contact optical profilometer (white light interferometer or confocal microscope). The optical probe scans the inner surface without physical contact, generating a high-resolution 3D topographical image of the surface. We measure the 2D parameters (Ra, Rz, Rq) and the 3D parameters (Sa, Sz, Sq), and we provide a 3D color map of the surface topography. This method is ideal for detecting localized defects such as pits, scratches, and corrosion spots.
• Replica-based roughness measurement (NTC 5802 – replica tape method for field measurement) – for field inspections of large-diameter pipes (e.g., in refineries or pipelines), we use replica tape. A piece of replica tape (a compressible plastic film) is pressed against the inner wall, creating a negative impression of the surface. The replica is then removed and measured in the laboratory using a stylus profilometer. We report the roughness parameters obtained from the replica, and we include a calibration correction for the replication process.
• Inductive and pneumatic roughness measurement (NTC 5803 – for pipes of small diameter) – for pipes with a diameter less than 25 mm, we use specialized probes based on inductance or air-gap measurement, which can access small bores. The probe measures the variation in inductance (or air pressure) as it traverses the inner surface, providing a measure of the average roughness. We report the Ra and Rz values, and the limitations of the method are noted.
• Measurement of roughness on curved surfaces (NTC 5804 – correction for curvature) – when measuring roughness on the inner surface of a curved pipe, we use a correction factor to compensate for the curvature effect on the measured roughness values. We report the corrected roughness values.

Correlation of Inner Wall Roughness with Fluid Flow Performance

Inner wall roughness directly affects the pressure drop and flow rate in pipelines. We use the measured roughness values to calculate the Darcy-Weisbach friction factor and to predict the flow performance using the Moody chart. This correlation is essential for the design of efficient piping systems and for the certification of components in the Colombian oil and gas sector.

• Calculation of the equivalent sand-grain roughness (ks) – NTC 5810 – Moody chart correlation – from the measured Ra or Rz values, we estimate the equivalent sand-grain roughness (ks), which is the parameter used in the Colebrook-White equation and the Moody chart to determine the friction factor. We provide the estimated ks value (in μm) and the corresponding friction factor for a specified Reynolds number.
• Pressure drop prediction using the Colebrook-White equation (NTC 5811 – hydraulic design calculation) – using the measured roughness, the pipe diameter, and the fluid properties, we calculate the expected pressure drop per unit length of pipe (in Pa/m). We report the predicted pressure drop and compare it with the design specifications.
• Effect of roughness on heat transfer (NTC 5812 – heat exchanger performance) – for heat exchanger tubes, we correlate the roughness with the heat transfer coefficient (using the Dittus-Boelter or Gnielinski correlations). We report the expected decrease in heat transfer efficiency (in %) due to the roughness.
• Effect of roughness on corrosion and fouling rate (NTC 5813 – corrosion and scaling prediction) – we correlate the measured roughness with the rate of corrosion (e.g., using the NACE corrosion model) and the rate of deposit formation. We provide an estimate of the expected service life reduction due to surface roughness.
• On-site friction factor measurement (NTC 5814 – field validation) – for installed pipelines, we can also perform a field measurement of the pressure drop and flow rate, and back-calculate the equivalent roughness from the actual operating data. We report the field-determined roughness and compare it with the laboratory-measured values.

Surface Damage and Defect Analysis – Corrosion, Pitting, and Wear

In addition to general roughness measurement, we analyze the inner surface for specific damage mechanisms such as pitting, corrosion, erosion, and wear, which can significantly increase roughness and compromise the integrity of the system. These analyses are critical for failure investigation and for the certification of pipes used in harsh environments.

• • Pitting depth and density measurement (ASTM G46 / NTC 5820 – pit evaluation) – using optical microscopy or profilometry, we measure the depth (in μm) and density (pits per cm²) of pits on the inner surface. We report the maximum pit depth, the average pit depth, and the pit density, and compare them with the corrosion allowances specified in the design.
  • Corrosion layer analysis (NTC 5821 – corrosion product identification) – we use scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to analyze the composition of any corrosion layer, scale, or deposit on the inner wall. We report the chemical composition of the layer and its thickness (in μm).
  • Erosion and wear scar analysis (NTC 5822 – wear track measurement) – for pipes that have experienced erosion due to sand or solid particles, we measure the depth and width of the wear scars or erosion marks using a profilometer. We report the wear depth (in μm) and the wear volume (in mm³).
  • Non-destructive evaluation (NDE) of internal defects (NTC 5823 – magnetic flux leakage or ultrasonic scanning) – for a comprehensive integrity assessment, we use magnetic flux leakage (MFL) or ultrasonic testing (UT) to detect and quantify internal defects (e.g., deep pits, cracks, wall loss) that may be related to roughness. We report the location and size of the defects.
  • Microstructural analysis of the pipe material (ASTM E3 / NTC 5824 – metallography) – for pipes made of metallic materials, we examine the microstructure of the inner wall to detect grain boundary corrosion, intergranular attack, or other microstructural changes that may affect the roughness and the structural integrity. We report the microstructural condition and any abnormalities.

Roughness Testing after Surface Treatment, Cleaning, and Conditioning

Inner wall roughness can be modified by surface treatments (shot peening, polishing, coating, or chemical etching) or by cleaning operations (pigging, flushing, chemical cleaning). Our tests evaluate the effectiveness of these processes and monitor the change in roughness, which is essential for quality control in the manufacturing and maintenance of piping systems.

• Roughness measurement before and after cleaning (NTC 5830 – cleaning efficiency assessment) – for pipes that have been pigged or chemically cleaned, we measure the roughness before and after the cleaning process, and we report the change in Ra, Rz, and Rmax. A decrease in roughness indicates effective removal of deposits or scale.
• Roughness after surface treatment (NTC 5831 – polishing, shot peening, or coating) – for pipes that have been polished, shot-peened, or coated, we measure the final roughness and verify that it meets the specification (e.g., Ra < 0.4 μm for a polished sanitary pipe). We report the roughness after treatment and the compliance with the specification.
• Roughness after thermal or chemical exposure (NTC 5832 – thermal aging and corrosion test) – we expose pipe sections to elevated temperature (e.g., 100 °C) or to chemicals (e.g., acid or alkali) and then re-measure the roughness to evaluate the effect of the exposure on the surface quality. We report the change in roughness and the severity of any surface degradation.
• Time-dependent roughness (NTC 5833 – roughness monitoring over time) – for pipes in long-term service, we perform periodic roughness measurements (e.g., every 6 months) to monitor the gradual increase in roughness due to corrosion and deposit accumulation. This provides data for predictive maintenance planning.
• Roughness of heat-affected zones (HAZ) – for welded pipes (NTC 5834) – we measure the roughness in the welded joint, the heat-affected zone, and the base metal, to evaluate any difference in surface quality that could affect the flow or cause corrosion initiation.

Complementary Analytical Techniques – Material Composition, Corrosion, and Deposits

To provide a comprehensive assessment of the inner wall condition, we complement the roughness measurements with chemical and material analyses that identify the composition of the pipe material, the nature of any deposits, and the potential for corrosion. These analyses are essential for root-cause analysis and for the certification of components for the Colombian oil, gas, and chemical industries.

• Chemical composition of the pipe material (ASTM E1621 / NTC 5840 – XRF analysis) – we use X-ray fluorescence (XRF) to determine the elemental composition of the pipe material (e.g., carbon, silicon, manganese, chromium, nickel) and to verify the grade (e.g., API 5L X52, AISI 316L). We report the composition and check it against the specified grade.
• Analysis of deposits and scale (NTC 5841 – XRD and TGA of deposits) – we collect the deposits or scale from the inner wall and analyze them using X-ray diffraction (XRD) to identify the crystalline phases (e.g., calcium carbonate, iron oxide, silica), and thermogravimetric analysis (TGA) to determine the organic content. We report the composition of the deposits and their likely origin.
• Corrosion product identification (NTC 5842 – SEM-EDS analysis of corrosion products) – we use SEM-EDS to analyze the corrosion products (rust, pitting products) and identify the presence of chlorides, sulfides, or other aggressive compounds. We report the composition and the morphology of the corrosion products.
• Carbon and oxygen content analysis (ASTM E1019 / NTC 5843 – for steels) – we measure the carbon and oxygen content of the pipe material to assess the risk of corrosion and hydrogen embrittlement, especially for high-strength steels used in sour service.
• Hardness testing and correlation with roughness (ASTM E18 / NTC 5844 – Rockwell hardness measurement) – we measure the hardness of the pipe material and correlate it with the roughness to identify any relationship between hardness and wear/corrosion resistance.

Test Report and Recognition in the Colombian Industrial and Infrastructure Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (profilometers, microscopes, XRF analyzers, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in Spanish and include:

• Full identification of the sample (pipe or component type, material, diameter, wall thickness, manufacturer, lot number, and service history).
• Detailed description of the test method applied (ISO/ASME/ASTM/NTC standard, measurement technique, scan length, number of measurements, and measurement conditions).
• Numerical results: Ra, Rz, Rq, Rmax, Sa, Sz (if 3D), equivalent sand-grain roughness (ks), pitting depth (μm), deposit thickness (μm), and friction factor (if calculated).
• Graphical data: roughness profiles, 3D surface maps, and correlation plots (e.g., roughness vs. friction factor).
• Comparative tables against the values specified by the client or against the limits of the NTC 5800 (Roughness measurement), NTC 5810 (Friction factor calculation), and the requirements of the ANH, the MinMinas, the SIC, and the DIAN for piping systems and industrial components.
• Photographs and micrographs (SEM) of the inner wall surface, showing the topography, pits, corrosion products, and any defects.
• Recommendations for design optimization (selection of a smoother material, application of internal coatings, adjustment of cleaning frequency) and for maintenance (pigging schedule, chemical treatment, or corrosion inhibition).
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Superintendencia de Industria y Comercio (SIC) for product registration and quality certification, by the Agencia Nacional de Hidrocarburos (ANH) and the Ministerio de Minas y Energía (MinMinas) for the validation of piping systems in the oil, gas, and mining sectors, and by the Dirección de Impuestos y Aduanas Nacionales (DIAN) for tariff classification and quality verification in the import of pipes, tubes, and related components. Additionally, we offer consulting services for the selection of materials with optimal surface roughness, the optimization of internal coatings and linings, and the implementation of predictive maintenance programs based on roughness monitoring. Our services support the efficiency, safety, and longevity of fluid-handling systems in the diverse and demanding industrial environments of Colombia, from the Caribbean refineries to the Andean and Amazonian pipelines and process plants.