Advances in ASTM G170 Rotating Cage: Geometry Effects on Fluid Dynamics and Wall Shear Uniformity (RIP2026-00088)

RHUAN SOUZA, Luan Carrera Santos, Mário Luis Ferreira da Silva, Bernardo Augusto Farah Santos, Maria Eduarda Dias Serenario, Gustavo Leitão Vaz, Jefferson Oliveira, Honória de Fátima Gorgulho, Jose Antonio Da Cunha Ponciano Gomes , Guillermo Vilalta-Alonso, Alysson Helton Santos Bueno

Universidade Federal de São João del-Rei, Universidade Federal de Sao Joao del-Rei, Universidade Federal de São João del-Rei, Universidade Federal de São João del-Rei, PETROBRAS, Governo Federal do Brasil, Universidade Federal de São João del-Rei, Labcorr – Universidade Federal do Rio de Janeiro, Universidade Federal de São João del-Rei, Universidade Federal de São João del-Rei

Evaluating the performance of materials and corrosion inhibitors in CO₂/H₂S environments is essential for ensuring the integrity and reliability of pipelines in the oil and gas industry. Among the laboratory techniques used to reproduce flow-accelerated corrosion (FAC), the Rotating Cage (RC) apparatus, described in ASTM G170, G184, and G202, is one of the most widely adopted. However, the standard rotating cage (SRC) exhibits well-documented limitations: strong nonuniformity in the distribution of wall shear stress (τw), differences between inner and outer sample faces, and pronounced edge effects. These issues generate excessive conservatism in corrosion rate values and reduce the representativeness of laboratory tests.
This work proposes two geometric modifications to the standard RC in order to improve the uniformity of hydrodynamic on the samples. An open cage model without the top and bottom disks (MRC-1), aimed at reducing asymmetries caused by restricted internal flow; and a model containing eight holes inclined at 45° (MRC-2), designed to increase fluid penetration and homogenize turbulence inside the cage. Both designs were evaluated through computational fluid dynamics (CFD) simulations using a multiphase Eulerian–Eulerian approach and a realizable k–ε turbulence model. Subsequently, the three RC configurations (SRC, MRC-1, and MRC-2) were experimentally tested in a 2-L autoclave at 120°C and 5 bar using API X65 steel in a CO₂/H₂S environment generated from sodium thiosulfate.
CFD results showed that the SRC exhibits strong asymmetry in τw and turbulent kinetic energy (TKE) distributions, particularly on inner surfaces, due to the single disk hole. The MRC-1 improved τwuniformity but significantly increased turbulence and shear stress magnitudes. In contrast, the MRC-2 achieved the best performance: the eight inclined holes created a more balanced flow pattern, reduced velocity and TKE gradients between sample positions, and yielded the highest τw uniformity index among all models.
The MRC-2 exhibited physicochemical behavior similar to the SRC but with much lower variability among samples, more homogeneous corrosion product formation, and reduced edge effects, one of the main sources of conservatism in RC testing.
Overall, the MRC-2 demonstrated the most effective improvement to the RC technique, offers more representative corrosion rate measurements, and increases the reliability of laboratory simulations of internal pipeline corrosion.