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Hydrogen Embrittlement of ASTM A320 L7 & L43 Grade Carbon Alloy Steel Bolts in Subsea Environments

Picture for Hydrogen Embrittlement of ASTM A320 L7 & L43 Grade Carbon Alloy Steel Bolts in Subsea Environments
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This paper reports an approach towards studying the susceptibility of materials to hydrogen embrittlement of several yield strength levels of ASTM A320 L7 & L43 grade carbon alloy material used for bolting . The test method used is based on ASTM E1820 using pre-cracked compact tension (CT) specimens in a seawater environment and under cathodic protection. The procedure has been to monitor the crack growth and the crack growth rate (CGR) at various constant stress intensity (K-levels) and at varying cathodic protection potentials. In this way these two parameters can be seen as representative of the susceptibility to embrittlement cracking of the materials at the specific stress intensity levels and as a function of the varying CP levels.The results indicate the strong effect that both stress intensity K-values and applied potential have on crack growth rates in environment and on the resulting susceptibility of the material to embrittlement. On the practical operational level the results also highlight the importance of actively monitoring and controlling cathodic protection (CP) potential levels as a means of increasing the allowable margin of error of the intersection between material quality design factors and the effect of the challenging environments of Oil & Gas subsea drilling and production operations.

Product Number: 51319-12785-SG
Author: Herman Amaya
Publication Date: 2019
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$20.00
$20.00
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A Fracture Mechanics Approach To Characterizing Hydrogen Embrittlement Of Fasteners

Product Number: 51321-16798-SG
Author: Herman E. Amaya, Behrang Fahimi, Ramgopal Thodla
Publication Date: 2021
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Materials properties that are used in specific oil and gas environments are de-rated due to the risks associated with hydrogen embrittlement cracking. In oil production environments the concern is for the onset of stress corrosion cracking (SCC), while in seawater environments the concern is for Hydrogen Induced Stress Cracking (HISC). Both are hydrogen embrittlement phenomena with the distinction being the source of hydrogen for each. In SSC the source of hydrogen is from the presence of H2S in the oil production fluids, and in HISC the source of hydrogen is from the dissociation of water from the cathodic protection system. This paper is focused on the latter phenomena and aims to characterize the susceptibility of carbon alloy steels as applied in fastener applications, in a seawater environment under cathodic protection.
Picture for Effect of Different Strength Levels, Coatings and Cathodic Charging Levels on the Hydrogen Embrittlement Resistance of AISI 4340 Bolting Material
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Effect of Different Strength Levels, Coatings and Cathodic Charging Levels on the Hydrogen Embrittlement Resistance of AISI 4340 Bolting Material

Product Number: 51320-14469-SG
Author: Timothy Haeberle, Evan J. Dolley Jr.
Publication Date: 2020
$20.00

AISI 4340 low-alloy steel (UNS G43400) is frequently used for critical bolting applications on subsea equipment in the oil and gas industry because of its ability to be heat treated to high strength levels while maintaining high toughness, even in large diameter bolting.  However, several field incidents resulting from hydrogen embrittlement of AISI 4340 bolting have brought into question the maximum hardness that should be specified for low-alloy steel bolting and whether zinc electroplating can contribute to hydrogen embrittlement of low-alloy steel bolting in subsea applications.  

In this evaluation, the relative hydrogen embrittlement resistance of AISI 4340 with different mechanical properties and surface conditions was determined using electrochemical pre-charging followed by step loading per ASTM F1624-121 in a 3.5% NaCl solution.  The test specimens were round, notched tensile test bars stressed in uniaxial tension to simulate the load on a tensioned bolt.  Testing was performed on material at two different strength levels with no coating, with zinc electroplate (both baked and un-baked), and with a phosphate coating to evaluate the effects of coatings.  The tests were performed in air, in the NaCl solution at open circuit potential, and in the NaCl solution at -950 mV, -1050 mV, and - 1250 mV (Ag/AgCl) to evaluate the effects of different levels of cathodic protection. 
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