Erwin Gamboa

Bond Slip Models for Uncorroded and Corroded Steel Reinforcement in Class-F Fly Ash Geopolymer Concrete

AbstractGeopolymer concrete is an innovative construction material that utilizes industrial by-product waste materials to form a cement replacement for concrete manufacture. In order to simulate the behavior of reinforced concrete at all load levels, an understanding of the bond between the reinforcement and the concrete is required. That is, at the serviceability limit state, the bond between the reinforcement and the concrete controls the formation of cracks, crack widening, and tension stiffening. Similarly, adequate bond between the reinforcement and the concrete is required at the ultimate limit state to ensure the full capacity of the reinforcement is obtained. Over time, the bond between the reinforcement and concrete can deteriorate due to corrosion, thus impacting the overall performance of a structure. This paper presents a wide-ranging study of the bond between reinforcement and geopolymer concrete including an investigation of the influence of corrosion. This study involved 102 pull-out test s...

High-pH inclined stress corrosion cracking in Australian and Canadian gas pipeline X65 steels

High-pH stress corrosion cracking is a form of environmental degradation of gas pipeline steels. The crack path is intergranular by nature and typically perpendicular to the maximum applied (hoop) stress (i.e. perpendicular to the pipe outer surface). Some unusual instances of cracks have been observed in Canadian and Australian X65 pipes, where cracks grow away from the perpendicular for considerable distances. This paper presents a comparative study in terms of crack morphology, mechanical properties and crystallographic texture for these Australian and Canadian pipe steels. It is shown that the crack morphologies are quite similar, the main difference being the angle at which the cracks propagate into the material. This difference could be explained by the different through-wall texture and grain aspect ratio measured in the two materials. The interdependency of crack tip plasticity, crack tip electrochemistry and anisotropy in microstructural texture seems to heavily affect the resulting inclined crack path.

TOMOGRAPHY OF INCLINED SCC CRACKS IN AUSTRALIAN GAS PIPELINES

Stress Corrosion Cracking (SCC) in pipeline steel occurs when an aggressive environment and tensile stresses act on a susceptible microstructure. Typically, SCC in gas pipelines tends to travel perpendicular to the hoop stresses in the through wall direction. Studies conducted on the TransCanada pipeline where a rupture had occurred revealed the incidence of SCC cracks whose crack path deviated at an angle from the normal. These inclined cracks have also been found in a pipeline in Australia which has lead to an increased need to better understand inclined SCC. This paper, based on the Australian pipeline, investigates the incidence rate, morphology, and observed interactions of inclined SCC in the Australian pipe.Copyright

Influence of Strain on Current Densities and Stress Corrosion Cracking Growth Rates in X65 Pipeline Steel

High pH stress corrosion cracking (SCC) in gas pipelines has been seen to grow along an incline angle rather than perpendicular to the outer surface. Crack tip strain enhanced electrochemistry has been previously postulated as a reason for the inclination, and recent computer simulations that take this effect into account produce realistic crack paths. This study attempts to determine the effect of strain on the electrochemical response of X65 steel, and the impact that the strain has on growth rates for inclined SCC. Potentiodynamic tests were conducted on X65 tensile specimens with residual plastic strain or in situ elastic strain. An increase of the current density up to 300% was observed within the SCC potential range. Computer simulations were also conducted to show the qualitative effect of this increase in current density on the growth rate, and results indicated that inclined SCC could grow to 50% wall thickness faster than straight SCC if the current density along the inclined angle is 20% higher...

An Investigation of Residual Stress, Hardness, and Texture on Stress Corrosion Cracking in a Gas Pipeline

Stress Corrosion Cracking (SCC) may be a serious problem in gas pipelines. This work studies the hardness and residual stress profiles in two nominally identical sections of adjacent pipe with similar environment and coating, one of which was affected by detectable SCC and the other that was not. The results show changes in texture, residual stress, plastic strain, and hardness at the pipe surface which may be responsible for the altered susceptibility to SCC.

Fatigue Crack Growth Comparison Between Sleeved and Non Sleeved Pipeline

A section of gas pipeline containing dormant stress corrosion cracks was removed from service and pressure cycled, and the crack growth from fatigue was measured. Crack growth was able to be conservatively calculated by BS7910. Parts of the pipeline section had composite repair sleeves placed over it in order to compare fatigue crack growth of sleeved and unsleeved cracks. Sleeved cracks consistently showed less crack growth than unsleeved cracks; this is believed to be due to reduced hoop stresses in the pipe under the composite repair sleeve and reduced crack opening. A simple model of the sleeve repair was developed which was consistent with the measured strains in the pipe. The application pressure of the sleeve repair affects the amount of stress reduction in the pipe and the amount of crack growth experienced. Two possible methods of repair of SCC affected pipelines were validated by this work.

Compositional aspects of cellulosic electrodes used for welding pipelines

The mechanical properties and compositional limits of line pipe for all major pipeline projects are subject to stringent project specific specifications and have substantial user input. The standards for welding electrodes do not have the same level of user involvement and permit significant latitude in terms of alloy design despite the fact that it is known the original electrode design can be markedly altered by elemental transfer as a result of changes in welding parameters and also the condition of the electrodes prior to welding. Several commercially available E8010 consumables have been evaluated under simulated field welding conditions. In addition, the influence of welding arc length and electrode conditioning were investigated. Significant variations in microstructure, hardness and Charpy impact toughness were noted and appear to be primarily related to the final chemical composition of the deposited weld metal. The weld metal carbon equivalent values ranged from 0.20 to 0.42 and all consumables contained additions of Ti and B in the flux coating which resulted in significant levels of B in the final deposited weld metal. It is recommended that the appropriate standards relating to the production and performance of cellulosic consumables be addressed to ensure complete disclosure of consumable formulations to the end user.Copyright