This paper describes the material selection and the relative testing for production tubing in two fields,
one onshore and the other offshore. Both fields are characterized by sour conditions with relatively low
concentrations of H2S. The offshore field has moderate temperature (102ºC), high salinity (~23 g/l Cl-),
high concentration of bicarbonates and 0.023 bar H2S partial pressure. Conversely, the onshore field has
a high temperature (193ºC), low salinity water phase (~2 g/l Cl-) and 0.08 bar H2S partial pressure.
The onshore field had a production tubing mechanical requirement of 110 ksi minimum yield strength
while the offshore field needed 115 ksi or preferably 125 ksi minimum yield strength for the Vacuum
Insulated Tubing (VIT). A preliminary study concluded that there was a possibility to use modified
martensitic stainless steels but a program of testing needed to be performed to assess the applicability of
these materials. Sulfide stress cracking, stress corrosion cracking, pitting and crevice corrosion tests
were performed under simulated downhole conditions, taking into account the conditions of maximum
susceptibility of these materials to these forms of corrosion.
Results revealed that the onshore wells environment would be too aggressive while the high strength
martensitic stainless steels could accommodate the conditions in the offshore wells.
Keywords: sulfide stress cracking, pitting, crevice corrosion, specified minimum yield strength,
modified martensitic stainless steels