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Nowadays, an increasing number of oil and gas transmission pipes are constructed with high-strength low alloy steels (HSLA; nonetheless, many of these pipelines suffer from different types of hydrogen damage, including hydrogen-induced cracking (HIC). Many studies are being done to investigate the role of key metallurgical and processing factors to limit the negative effects of HIC in HSLA steel pipes.

Fatigue crack growth rate (FCGR) data were measured in high pressure hydrogen gas versus stress intensity factor range (ΔK) in specimens removed from a X100 welded steel pipe. Three distinct regions of the pipe weld were examined: base metal, weld fusion zone, and heat affected zone. Tests were performed at a load ratio (R) of 0.5, frequency of 1 Hz, and at a hydrogen gas pressure of 21 MPa. Tests were also performed in air at 10 Hz as a reference. Fatigue crack growth rates were observed to be over an order of magnitude higher for tests performed in hydrogen compared to the rates from tests in air. Residual stress measurements were collected on identical specimens cut from the base metal, weld, and heat affected zone to account for their influence on measured FCGR data. The slitting method provided residual stress and residual stress intensity factor (Kres), the effect of which was removed from the FCGR data using Knorm in order to provide a more direct comparison of crack growth resistance of the base metal, weld and heat affected zone. Prior to accounting for residual stress, FCGR in hydrogen gas appeared to be highest in the weld fusion zone. After accounting for residual stress effects, the weld fusion zone FCGR data converged to the base metal FCGR data, which underscores the importance of accounting for residual stress effects when assessing fatigue performance.

Nowadays, an increasing number of oil and gas transmission pipes are constructed with high-strength low alloy steels (HSLA; nonetheless, many of these pipelines suffer from different types of hydrogen damage, including hydrogen-induced cracking (HIC). Many studies are being done to investigate the role of key metallurgical and processing factors to limit the negative effects of HIC in HSLA steel pipes. The thermomechanical control process (TMCP) is a microstructural control technique that avoids the conventional heat treatment after hot rolling and attempts to obtain the desired mechanical properties during the forming process. Recent research has shown that TMCP provides high HIC resistance without adding high amounts of alloying elements or applying expensive heat treatments. However, there is an incipient knowledge on predicting HIC behavior, both in susceptibility and kinetics, in HSLA steel pipe when it is exposed to hydrogen charging service conditions. This paper presents a review of the current developments of HSLA and TMCP of pipeline steels, as well as the phenomenological and empirical models proposed to predict the kinetics of HIC as a function of key parameters such as heat treatments and microstructures, especially nature and spatial distribution of non-metallic inclusions and the hydrogen permeation rate and the mechanical and fracture mechanics properties. [ABSTRACT FROM AUTHOR]

Fatigue crack growth rate (FCGR) data were measured in high pressure hydrogen gas versus stress intensity factor range (ΔK) in specimens removed from a X100 welded steel pipe. Three distinct regions of the pipe weld were examined: base metal, weld fusion zone, and heat affected zone. Tests were performed at a load ratio (R) of 0.5, frequency of 1 Hz, and at a hydrogen gas pressure of 21 MPa. Tests were also performed in air at 10 Hz as a reference. Fatigue crack growth rates were observed to be over an order of magnitude higher for tests performed in hydrogen compared to the rates from tests in air. Residual stress measurements were collected on identical specimens cut from the base metal, weld, and heat affected zone to account for their influence on measured FCGR data. The slitting method provided residual stress and residual stress intensity factor (K res ), the effect of which was removed from the FCGR data using K norm in order to provide a more direct comparison of crack growth resistance of the base metal, weld and heat affected zone. Prior to accounting for residual stress, FCGR in hydrogen gas appeared to be highest in the weld fusion zone. After accounting for residual stress effects, the weld fusion zone FCGR data converged to the base metal FCGR data, which underscores the importance of accounting for residual stress effects when assessing fatigue performance. [ABSTRACT FROM AUTHOR]

In order to comparatively assess near-neutral pH stress corrosion cracking (NNpH-SCC) resistance of pipeline steels with different strength, constant load tests in NS4 solution purged with 5%CO2-N2 gas mixture were conducted on American Petroleum Institute (API) grade X70, X80 and X100 pipeline steels. Experimental results show that pit cracks appeared on the surface of X70 steel and non-pit cracks appeared on X100 steel. However, for X80 steel both pit cracks and non-pit cracks were observed, but pit cracks dominated. The near-neutral pH SCC resistance decreased in the order of X70, X100 and X80 at the same applied stress level. [ABSTRACT FROM AUTHOR]