Material behavior in extreme conditions: L450Q (X65Q) corrosion resistance, strength and toughness variation following exposure to environments with elevated H2S partial pressure

AUTHOR/S: Roberto Morana, Laura Alleva, Giuseppe Mortali, Stefano Crippa, Federico Tintori, Mariano Armengol Lamazares PAPER PRESENTED TO: NACE CORROSION CONFERENCE 2012, March 11-15, 2012 Salt Lake City, Utah, USA

ABSTRACT

Oil and natural gas transporting plants in arctic field (i.e. North America, Kashagan, Karachaganak) normally operate at temperatures up to 100°C or even more. During the shut down operations, in winter time, pipelines materials reach very low temperatures (-40°C) and are subjected to a severe environment with high concentration of hydrogen sulfide (5-20%) and to an important step in pressure in the subsequent re-starting operations. Therefore, there is the need of assessing material performances in presence of H2S partial pressure up to 20 bar or more.

The present work assessed the following issues for L450Q (X65Q) grade Carbon steel for linepipe:

  • the effect of hydrogen on material strength and toughness at low temperatures.
  • the general corrosion and stress corrosion cracking resistance in extreme conditions with high pressure of H2S looking for a window of applicability.

Ductile-brittle transition curve and mechanical properties were evaluated by means of Charpy-V, tensile and Crack Tip Opening Displacement (CTOD) methods for as received materials and after exposure to H2S containing environment. Furthermore autoclave exposures of coupons and stressed samples (Four Point Bent Beam, FPB) in environment containing elevated values of H2S partial pressure (10 and 16 bars) at different pH (3.5, 4.5) were carried out.

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