X-Ray CT inspection limitations in a thick-walled LPBF hydraulic manifold : an industrial case study

Bartolj, Jan (author), Trajkovski, Ana (author), Majdič, Franc (author)

Metal additive manufacturing (AM) enables compact hydraulic manifolds with curved internal channels, reduced part count and integrated functionality. However, these benefits also create major inspection challenges, especially in thick metallic sections containing closely spaced and intersecting passages. This study examines the practical use of X-ray computed tomography (CT) for an industrial hydraulic manifold manufactured from maraging steel MS1 by laser powder bed fusion (LPBF). Selected cross-sections from the reconstructed CT volume were compared with the nominal computer-aided design (CAD) geometry and evaluated using a qualitative interpretability classification supported by comparative image contrast-to-noise ratio (CNR) analysis and approximate projected steel thicknesses. Clearly interpretable regions showed higher and more consistent CNR, whereas geometrically congested regions generally exhibited lower and more variable local contrast. However, projected material thickness alone did not determine interpretability, indicating an additional influence of geometric overlap, orientation and reconstruction artefacts. Particular attention was given to a channel wall adjacent to a locally collapsed external support structure. No spatially persistent through-wall discontinuity was identified, although smaller defects, local wall thinning and metallurgical changes could not be excluded. A pneumatic immersion test at 0.8 MPa showed no visible bubble formation or observable pressure decrease. This pressure exceeded the expected operating pressure of the affected relief or tank channel but was substantially below the 35 MPa maximum intended pressure of the pressure-side circuits and therefore did not constitute structural qualification. The study demonstrates that whole-component CT can provide useful local inspection information for complex LPBF manifolds, but its reliability depends strongly on local geometry and acquisition conditions. Quantitative image assessment and complementary functional testing may therefore be required when CT results are insufficient for complete qualification.

• Language: English
• Keywords: laser powder bed fusion, hydraulic manifold, X-ray computed tomography, non-destructive testing, internal channels, leak testing
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 19 str.
• Numbering: Vol. 16, iss. 9, art. 969
• PID: 20.500.12556/RUL-188481
• UDC: 621.386:621.762
• ISSN on article: 2075-4701
• DOI: 10.3390/met16090969
• COBISS.SI-ID: 292157699
• Publication date in RUL: 23.09.2026

Record is a part of a journal

• Title: Metals
• Shortened title: Metals
• Publisher: MDPI AG
• ISSN: 2075-4701
• COBISS.SI-ID: 15976214

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: lasersko taljenje v prašni postelji, hidravlični bloki, računalniška tomografija z x-žarki, nedestruktivno testiranje, notranji kanali, testiranje puščanja

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0231
• Name: Tribologija