Qualification of Seamless X60QOS and X65QOS Line Pipe Grades for Extreme Sour Service Conditions with Partial Pressure of H2S beyond 1 Bar

Seamless X60QOS and X65QOS line pipes are widely used for offshore and onshore Sour Service applications. Sour Service refers to the risk of hydrogen related cracking as Sulfide Stress Cracking (SSC). The International standard (NACE MR0175 / ISO 15156) provides requirements for assessing the resistance to SSC, specifically on how to qualify for use in region 3 of the environmental severity diagram (Figure 1 in paragraph of part 2). It is requested to expose materials in an acid solution saturated by 1 bar of H2S (NACE TM0177 Solution A) and to apply a tensile stress above 80% AYS by means of different methods: uniaxial tensile, C-ring or Four-Points Bend. However, for very sour fields presenting H2S partial pressures much higher than 1 bar, the preservation of the SSC resistance might be questioned and is presently a major concern for the O&G industry.
The present paper is dedicated to the evaluation of the SSC resistance of seamless quenched and tempered X65 grades, including the girth weld in the standard NACE TM0177 Solution A up to 15 bar of H2S partial pressure. Corrosion tests consisted of four-point bend tests performed in autoclave vessels. Different test configurations were investigated as specimen sampling locations through the wall thickness and surface state preparation.

Product Number: MPWT19-15127
Author: Florian THEBAULT, Laurent LADEUILLE, Harold EVIN, Laurent LAMPS
Publication Date: 2019
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Role of Metallographic Characterization in Failure Analysis – Case Studies

Product Number: MPWT19-14379
Author: Syed Ahsan Ali
Publication Date: 2019

Conducting a materials failure analysis requires a carefully planned series of steps intended to
arrive at the cause of the problem. Consistent with the current trend towards better accountability
and responsibility, failure analysis purpose has been extended in deciding which party may be
liable for losses, be they loss of production, property damage, injury, or fatality [1]. Hence it
increases the importance of proper implementation of characterization tools in failure analysis to
rightly identify the failure mode.
Present work discusses a few case studies to shed light upon the importance of the metallurgical
characterization tools and techniques in identification of correct failure mode. Some typical case
studies where metallography plays a very important role have been discussed, such as improper
welding joints which led to premature failure, sensitization and stress corrosion cracking in S.S.,
improper heat treatment and forging indicated the microstructures which led to the premature
failure. These cases are examples of only a few laboratory based investigations which justify that
without metallography it is not possible to diagnose the causes of premature failures.
Generally, examination of failed components commence with the low-power stereomicroscope
whereas hand-held magnifying lenses are still in wide use by experts to study fractures mostly
limited now for field purpose [2]. Metallographic examination typically is performed after nondestructive
and macroscopic examination procedures while using the light optical microscopy
which helps to assess the failure mode with respect to material defects, shortcomings in
processing, metallurgical changes etc. Since light optical microscopy has limited value for direct
observation of fracture surfaces (more limited for metals than non-metals), with still more factual
information can be gathered by scanning electron microscopy at higher magnification.

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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

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