In this research paper, the failure pressure predictions were obtained for a pipeline section by analyzing a combined corrosion defects, which joins together a general corrosion and a pitting corrosion defects. Well-known conventional mathematical methods were used in this study to predict the failure pressure of corroded steel pipelines, such as: B31G, RSTRENG-1, Shell-92, DNV, PCORR, and Fitnet FFS. The equations reported for corrosion defects with more complex characteristics developed by Choi et al., and Cronin et al. were also used. Furthermore, Finite Element (FEM) is one of the most employed nonlinear methods because of its good response of pipeline failure prediction under the corrosion mechanism. So, FEM methodology results the least conservative in comparison with the others mathematical models, according to the literature, for this reason it was used to compare the standard deviation  of the methods. Failure pressure predictions determined that the most conservative methods were: Shell-92, Fitnet FFS, Choi's method, B31G, RSTRENG-1, Cronin´s method, PCORR and DNV, in that order.

This paper presents experimental research work on the combination of grinding and wet welding techniques to repair T-welded connections employed in the construction of offshore structures. A longitudinal rectangular grinding profile was performed at the weld toe of T-welded connections for localized cracking material removal. Two different grinding depths of 6 mm and 10 mm were performed in the welded connections to eliminate two different level of damage depth. Subsequent wet welding was applied in the grinded region to repair the grinded material. The wet welding was performed in a hyperbaric chamber simulating three different water depths: 50 m, 70 m and 100 m (shallow water). Once the combined repair techniques were performed, further experimental work was done to characterize the mechanical behavior of the repaired structures. The mechanical characterization was done with tensile, Charpy tests and Vickers Hardness tests. The region of interest from the structures was the weld toes the grinded-wet welding repair of the T-welded connections. Subsequent scanning electron microscopy (SEM) was also performed to examine the developed microstructures in the T-welded connection. The results showed that the combination of the repair techniques can restore the mechanical properties of the damaged structures. This was demonstrated by the measurement of the ultimate tensile strength, which were similar to those measured with no repair applied techniques. But the Charpy energy values were quite lower to those previously measured. This behavior was attributed to the level of porosity formed by the high level of gases created during the welding process for the simulated water depths, which were more severe at the higher water depth resulting in pore formation

Abstract:The mechanical behavior of API 5L X52 steel with planar type laminations was studied in the present work. Planar laminations were proposed in the base metal (BM), heat affected zone (HAZ) and welding bead (WB). Three-dimensional finite element (FE) models, kinematic hardening and mechanical properties for BM, HAZ, and WB were activated in the finite element program. The results showed that crack propagation corresponds to the direction of the main stress. For a crack length (2a) of 10.01 mm, crack propagation may occur at the right crack tip towards the outer wall of the BM. For 2a of 15.12 mm, crack propagation was located on the right crack tip and propagates to the inner wall. For 2a of 17.12 mm, crack propagation was observed at the left crack tip and propagates to the outer wall in the BM. The results achieved by FEM agree when compared with real laminations in API 5L pipelines.

This study presents, for the first time, the mechanical behavior of API 5L pipeline steels X42, X52, X60, X70, X80, and X100 with external and internal corrosion defects as well as a combination of both defects that has been named external–internal corrosion defects. The conventional methods to predict failure pressure in corroded pipes, such as B31G, RSTRENG-1, SHELL, DNV-99, PCORRC, and FITNET FFS, have also been discussed in this article. In addition, pipeline failure pressure has been estimated using the finite element method, considering that it is the best approach to calculate actual failure pressure. The external and internal corrosion defect investigated in this research manifests as a rectangular shape with spherical ends at the edges. When the external–internal corrosion defect appears, failure pressure data decrease dramatically because of severe damage. This is due to the decrease in the ligament (effective area) caused by the corrosion defect. To have a good estimation of the pipeline failure pressure with an external–internal corrosion defect, DNV-99 method can be used with acceptable certainty.

The stress concentration factors (SCFs) in welded connections usually occur at zones with high stress levels. Stress concentrations reduce the fatigue behavior of welded connections in offshore structures and cracking can develop. By using the grinding technique, cracking can be eliminated. Stress concentration factors are defined as a ratio of maximum stress at the intersection to nominal stress on the brace. Defining the stress concentration factor is an important stage in the fatigue behavior of welded connections. Several approaches have evolved for designing structures with the classical S-N approach for estimating total life. This work correlates to the stress concentration factors of T-welded connections and the fatigue behavior. Stress concentration factors were computed with the finite element employing 3D T-welded connections with intact and grinding depth conditions. Then, T-welded connections were constructed with A36 plate steel and welded with E6013 electrodes to obtain the stress-life (S-N) approach. The methodology from previous works was used to compute the SCF and fabricate the T-welded connections. The results indicated that the grinding process could restore the fatigue life of the T-welded connections for SCFs values in the range of 1.29. This value can be considered to be a low SCF value in T-welded connection. However, for higher SCF values, the fatigue life decreased, compromising and reducing the structural integrity of the T-welded connections.Nowadays, fatigue work on T-welded connections has been carried out, repaired by U-shape grinding under plane stress condition [7][8][9]. A better approach was achieved by performing 3D finite element modelling and applying empirical formulations [8,10]. Unfortunately, the empirical formulations can only be applied for a U-shape grinding depth of 27% of the plate thickness. For example, in the industry, deep cracks can be identified at