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Generally, 316L stainless steel instrumentation tubes working in a humid environment with a large amount of Cl− all the year round have serious corrosion problems, so the stainless steel substrate should be gradiently coated with nano-ZrO2/α-Al2O3 slurry. In this article, the slender 316L stainless steel tube was first ground by magnetorheological fluid and then coated with the slurry, which can not only increase the contact area between the coating and the substrate but also prevent the generation of new substances that have adversely affected the adhesion of the coating. The properties of the samples were characterized and analyzed; the results showed that the substrate ground by magnetorheological fluid is more favorable for bonding with coating under the grinding conditions that the speed of the tube is 210 rpm, magnetic induction intensity is 40.83 mT, and mass ratio of micron and submicron magnetic particles is 2.3. The coating prepared under the above conditions has uniform thickness, flat surface, and can better inhibit the diffusion of Cr of the substrate to its surface. It can be obtained from corrosion resistance analysis that the coating has the highest self-corrosion potential of −0.016 V and the lowest corrosion current density of 0.491 μA/cm2, which indicate that the coating has the strongest corrosion resistance. According to the composition analysis of the coating, the composition of the corroded coating is similar to that of the coating itself, but accompanied by a small amount of Fe, which indirectly indicates that the coating is relatively compact, the coating is well bonded with the substrate, and the coating can protect the substrate; thus, the service life of 316L stainless steel instrumentation tubes is extended.

For the purpose of a better understanding of the mechanical behavior of pipe joints’ interface which is critical for the integral performance of a pipe system, and excessive torsional loading that is typical for their interfacial failure, the interfacial behavior of adhesive bonded pipe joints under torsion loads is theoretically studied throughout the full-ranged failure process based on a local bond-slip law with hardening and exponential softening. Firstly, closed-form solutions for the interfacial shear stress distribution and load–displacement response are derived to describe the four basic loading stages. Secondly, a simplified law is used by changing the exponential softening law into a tri-linear one to make the comparison. According to the analytical solutions of two laws, the influences of the bond length on load–displacement curve including the ultimate loads and relative slips are discussed, with the similarities and differences between the two laws being studied. Thirdly, by introducing a dimensionless damage parameter, the results of the finite element method (FEM) using ABAQUS modeling are compared with analytical results. Based on these coincident results, the parametric studies of bond lengths and ratios of torsion stiffness on specific cases were conducted to explain the stress transfer mechanism and interface crack propagation. Both their ultimate bearing capacity and ductility improve in an increase of bond lengths, while the ductility reduces as the ratio of torsion stiffness increases. The outcomes of this paper are helpful to improve the safety and applicability of bonded pipe joints in engineering design and application.

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