Increase In Collapse Pressure Research Articles

Effect of Strain Hardening on Increase in Collapse Pressure during the Manufacture of ERW Pipe

Plastic deformation during the manufacture process of electric resistance welded (ERW) pipe determines the stress–strain relationship of the steel pipe, which affects the collapse pressure of offshore pipelines. To track the deformation history of the pipe, the entire process was simulated via finite element analysis using a solid element. A material model that considered both the Bauschinger effect and strain hardening was adopted. Various sizes of pipe cross-sections were simulated. As greater compression was applied during the sizing process, the strain hardening effect became more significant, so that the compressive yield strength was increased in the circumferential direction. The strain hardening effect was most prominent for a smaller diameter-to-thickness ratio (D/t), so that an increase in the collapse pressure could be obtained with a larger sizing ratio. Therefore, current design criteria for the collapse pressure recommended by Det Norske Verita (DNV) and API could be enhanced for a smaller D/t to consider the strain hardening effect during the sizing process.

Mechanical Properties of a Biodegradable Balloon-expandable Stent From Poly(L-lactide) for Peripheral Vascular Applications

Background: Biodegradable polymeric stents represent a competitive approach to permanent and absorbable metallic stents for vascular applications. Despite major challenges resulting from the mechanical properties of polymeric biomaterials, these stent concepts gain their attraction from their intrinsic potential for controlled biodegradation and facile drug incorporation. This study demonstrates the mechanical properties of a novel balloon-expandable slotted tube stent from PLLA. Method of Approach: Polymeric balloon-expandable slotted tube stents (nominal dimensions: 6.0×25mm) were manufactured by laser machining of solution cast tubes (I.D.=2.8mm, d=270±20μm) from biodegradable (1) PLLA and (2) PLLA/PCL/TEC. The stents were tested in vitro for their mechanical properties: deployment, recoil, shortening, collapse, and creep behavior under a static load of 100mmHg. In vitro degradation was performed in Sørensen buffer solution at 37°C. After 0∕2∕4∕8∕12∕24 weeks the remaining collapse stability and molecular weight were assessed. Results: All stents could be deployed by balloon inflation to 8bar at 1bar∕min (PLLA) and 3bar∕min (PLLA/PCL/TEC). Recoil, shortening, and collapse pressure were: 2.4%∕3.4%∕0.67bar (PLLA), and 8.8%∕2.3%∕0.23bar (PLLA/PCL/TEC). A static load of 100mmHg induced pronounced creep processes in the PLLA/PCL/TEC stent. The PLLA stent remained patent and exhibited no creep propensity. During in vitro degradation an increase in collapse pressure was observed (maxima at 12w: 1.3bar (PLLA), 0.7bar (PLLA/PCL/TEC)). At 24 weeks, molecular weight was decreased by 28% (PLLA), and 52% (PLLA/PCL/TEC). Conclusions: Stents fabricated from pure PLLA exhibited adequate mechanical properties. The slow permissible deployment rate, however, limits their potential application range and demands further development.

Interfacial Interactions of Cations with Amphiphilic Dihydroxyphosphonyl-calix-[4]-arene Mesosystems

Two novel amphiphilic phosphorylated-calix-[4]-arenes, 5,11,17,23-tetrakis(dihydroxyphosphonyl)-25,26,27,28-tetradecyloxy-calix-[4]-arene and 5,11,17,23-tetrakis(dihydroxyphosphonyl)-25,26,27,28-tetradodecyloxy-calix-[4]-arene, have been synthesized, and their interactions with the cations Na+, K+, Mg2+, and Ca2+ have been measured at varying concentrations of the chloride salts. The systems were studied both at the air−water interface and in aqueous suspension as colloidal nanostructures. In the Langmuir experiments, monolayer expansion and increase in collapse pressure were observed for Na+ at a concentration of 145 mM. For Mg2+, there was monolayer expansion accompanied by the formation of a second phase at a subphase concentration of 30 mM. In contrast, in the case of Ca2+ there is an apparent contraction of the monolayer. The nanostructures were imaged by means of atomic force microscopy in the noncontact mode. As aqueous dispersions, no change in size or stability of the colloidal systems was observed with the monovalent cations; however, for the divalent cations at concentrations above 3 mM for Mg2+ and 3 mM for Ca2+ there is aggregation and flocculation of the dispersions.

Anion and Cation Interactions withp-Dodecanoylcalix[4]arene Monolayers at the Air−Water Interface

The Langmuir compression isotherms of p-dodecanoylcalix[4]arene have been studied on subphases containing varying concentrations of group IA salts. The effect of anions on the stability of the monolayers shows that, for acetate and bicarbonate, there is a large increase in collapse pressure, when sodium is the countercation. In the case of cation effects, rubidium chloride shows a large stabilization of the monolayer.

Langmuir and Langmuir−Blodgett Films of NLO Active 2-(p-N-Alkyl-N-methylamino)benzylidene-1,3-indandioneπ/A Curves, UV−Vis Spectra, and SHG Behavior

We study 2-(p-N-hexadecyl-N-methylamino)benzylidene-1,3-indandione (1a) as a model compound for the preparation of nonlinear optically (NLO) active Langmuir−Blodgett (LB) layers. The pressure−area (π−A) isotherm of (1a) at the air−water interface is investigated. A limiting area of 0.60 ± 0.02 nm2 per molecule is found. The alternate-layer LB deposition of compound (1a) and an inert spacer, cadmium stearate, at different surface pressures is performed. The effects of temperature and delay time between spreading of the Langmuir film and the deposition of the LB films are studied. An increase of collapse pressure from 20 to 30 mN/m is observed as the delay time increases. UV−vis spectra indicate a uniform transfer of (1a) and show compression-induced changes as a function of the deposition conditions. A split of the absorption maximum is observed for LB films deposited at higher pressures and lower temperatures. The two bands can result from two different molecular electronic transitions, affected by the aligning influence of the surface, and the different environments in the film compared to solution. Alternatively, these two bands can be associated with (at least) two different conformers. The orientation of the transition moments is evaluated on the basis of polarized UV−vis spectra at different angles of incidence, and found to be 40−44°. Significant second harmonic (SH) generation by the LB films is observed. Analysis of the SH response gives a tilt angle of 44°, in agreement with the finding from UV absorbance.