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O2 Contamination in Ssc / Hic Qualification Test Environments – Impact on Test Results and Discussion on Acceptable Limits

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It is a well-admitted fact that oxygen contamination shall be avoided during standard H2S cracking tests. Until 2016 NACE technical methods related to H2S cracking resistance evaluation (e.g. NACE TM0284 and NACE TM0177) only gave general suggestions about O2 pollution. For instance it was recommended that ‘tests vessels shall be capable of being purged to remove O2’ and also that ‘O2 contamination is evident by a cloudy appearance’. In the 2016 revisions of NACE TM0177 and NACE TM0284 documents quantitative limits of O2 contamination were included:- Test method must ensure that the test solution contains less than 50 mass. ppb dissolved O2 before the introduction of H2S.- A more stringent limit of 10 ppb max. is imposed when testing Corrosion Resistant Alloys (CRA) or high strength low alloy steels (> 80 ksi).However the scientific basis of these values have not been well-established yet and there is still a lack of available experimental data to illustrate the potential impacts of small dissolved oxygen contents on the cracking resistance of different materials. In addition while the revised test methods explicitly address initial contamination of the test solution before H2S introduction they do not consider a continuous oxygen supply during testing. This possible continuous O2 contamination is extremely difficult to eliminate and control for example in case of poor laboratory practices oxygen ingress may arise by permeation through polymer tubings used for the tests or in case of a lack of tightness of gaskets.In order to better understand the impact of O2 contamination on H2S cracking a 3-years Joint Industrial Project (JIP) was launched at the end of 2015. The objectives were to evaluate if continuous O2 contamination can affect H2S cracking test results. A range of steel grades covering different types of O&G applications such as line pipe OCTG and flexible wires were used. Sulfide Stress Cracking (SSC uniaxial tensile as well as 4 point-bend tests) and Hydrogen Induced Cracking (HIC) tests were conducted with well-controlled and continuous O2 contamination. Three levels of O2 partial pressures in the gas feed corresponding to 300 ppb 50 ppb and less than 10 ppb dissolved O2 were used. These levels were selected to simulate poor deaeration and the current limits specified in the last standard revisions respectively.In parallel to the standard qualification tests hydrogen permeation and weight-loss corrosion experiments were performed with the same test matrix covering all regions of the SSC severity diagram. This paper aims at sharing the main results of this JIP. 

Product Number: 51319-12894-SG
Author: Christophe Mendibide
Publication Date: 2019
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There is an increasing need to define the operating envelope for materials typically used as oil country tubular goods. This paper reports results of sulfide stress cracking (SSC) tests that were performed in mild sour environment at temperatures below 107°C.
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51318-10931-Impact of oxygen pollution on H2S corrosion and hydrogen permeation

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Author: Martien Duvall Deffo Ayagou / Christophe Mendibide / Claude Duret-Thual / Jean. Kittel / Nicolas Ferrando
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Role of Non-Metallic Inclusions and the Microstructure Constituents on HIC Performance

Product Number: MPWT19-14439
Author: Amro Al-Hattab1,Diaa Elsanosy2, Gaurav Tomer3, Abdullah Al-Jarbou4
Publication Date: 2019
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With increasing oil & gas demand and depletion of sweet reserves, oil & gas companies in the regional
economies are focusing towards the exploitation of sour resources. This necessitates the use of pipelines
and down-hole tubing made from special steels with significant resistance to hydrogen-induced cracking
(HIC). These steels are produced through specific technologies for enhanced chemical composition control
and microstructural engineering to incorporate the required strength, weld ability and improved HIC
resistance. It is well established that the HIC initiates at sites with microstructural heterogeneities whether
due to presence of gross nonmetallic inclusions or the micro-structural constituents. The presence of central
segregation further aggravates the conditions particularly when the final pipe sizes require the longitudinal
slitting of the coils. Presence of non-metallic inclusions in the steel makes it vulnerable to hydrogen-induced
cracking under wet H2S environment. The mechanism of HIC begins with the generation of hydrogen atoms
by corrosion reaction of H2S and Fe in the presence of free water. The hydrogen atoms then diffuse into
steel and accumulate around the inclusions. The higher number of inclusions equates to the more sites
available for hydrogen adsorption. Recombination of hydrogen atoms to H2 molecules builds up a heavy
gas pressure in the interface between matrix and inclusions. Cracking initiates because of the tensile stress
field caused by hydrogen gas pressure and crack propagates in the surrounding steel matrix. The
longitudinal slitting exposes the internal microstructural abnormalities to the skelp edges which are then
incorporated in the thermally stressed weld zone. While the post-weld heat treatment (PWHT) mostly
homogenizes the weld zone microstructure, the presence of excessive central line features cannot be
completely removed thereby making this zone more prone to HIC attack
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