TY - THES

T1 - Corrosion Fatigue of a CrMnNiMoN Austenitic Stainless Steel for Drillcollars

AU - Bachhuber, Petra

N1 - embargoed until 29-10-2023

PY - 2018

Y1 - 2018

N2 - Within the application of high performance alloys in the oil and gas industry, high demands towards the materials are set. Especially during drilling operation exposure to high temperature, high stresses and corrosive conditions present a challenging environment. Schoeller-Bleckmann Oilfield Technology GmbH in cooperation with Bohler special steels successfully designs and manufactures several of these components. Special focus is put on the material selection for non-magnetic drillcollars applied as part of the bottom hole assembly (BHA) in the drillstring. Within this thesis the influence of the alloy composition of a CrMnNiMoN alloy and its resistance against corrosion fatigue failure was investigated. In order to determine the corrosion fatigue and fatigue limits, S-N curves have been measured, applying high cycle fatigue on the samples. Fatigue failure is the most severe failure mode for steel components; therefore the samples were exposed to cyclic tensile loads. One sample set of 15 specimens was exposed to high chloride ion concentration and high temperature, the other sample set was exposed to high temperature and an inert medium. This allowed to determine the impact of corrosive conditions on the durability in dynamic stress environment. In order to evaluate the failed samples in corrosive conditions further, the areas of failure were examined under the microscope. To gain further insight on the alloy properties in aggressive environment, current density potentials were recorded to determine the corrosion- and re-passivation potential. Aim of this thesis was to draw comparisons with previously developed alloys to evaluate the applicability of the CrMnNiMoN alloy P511. It is proven that P511 generally shows slightly lower fatigue strength in non-corrosive environment, but significantly higher corrosion fatigue strength in aggressive conditions than comparable austenitic stainless steel alloys [1].

AB - Within the application of high performance alloys in the oil and gas industry, high demands towards the materials are set. Especially during drilling operation exposure to high temperature, high stresses and corrosive conditions present a challenging environment. Schoeller-Bleckmann Oilfield Technology GmbH in cooperation with Bohler special steels successfully designs and manufactures several of these components. Special focus is put on the material selection for non-magnetic drillcollars applied as part of the bottom hole assembly (BHA) in the drillstring. Within this thesis the influence of the alloy composition of a CrMnNiMoN alloy and its resistance against corrosion fatigue failure was investigated. In order to determine the corrosion fatigue and fatigue limits, S-N curves have been measured, applying high cycle fatigue on the samples. Fatigue failure is the most severe failure mode for steel components; therefore the samples were exposed to cyclic tensile loads. One sample set of 15 specimens was exposed to high chloride ion concentration and high temperature, the other sample set was exposed to high temperature and an inert medium. This allowed to determine the impact of corrosive conditions on the durability in dynamic stress environment. In order to evaluate the failed samples in corrosive conditions further, the areas of failure were examined under the microscope. To gain further insight on the alloy properties in aggressive environment, current density potentials were recorded to determine the corrosion- and re-passivation potential. Aim of this thesis was to draw comparisons with previously developed alloys to evaluate the applicability of the CrMnNiMoN alloy P511. It is proven that P511 generally shows slightly lower fatigue strength in non-corrosive environment, but significantly higher corrosion fatigue strength in aggressive conditions than comparable austenitic stainless steel alloys [1].

KW - Korrosion

KW - CrMnNiMoN

KW - Schwingungsrisskorrosion

KW - nicht-magnetische Schwerstangen

KW - Corrosion Fatigue

KW - CrMnNiMoN

KW - Austenitic Stainless Steel

KW - Non-magnetic Drillcollars

M3 - Master's Thesis

ER -