Sour service requirements for drilling equipment
This questions pops up frequently: What are the “NACE” requirements for drilling equipment? i.e. drill pipe, drill collars, and crossovers? The answer is not about metallurgy. According to ISO 15156 / NACE MR0175, drilling equipment is protected not by controlling the metallurgy but by controlling the drilling mud. Drilling equipment requires high strength and low cost, this means High Strength Low Alloys such as AISI 4145 are heat treated beyond the 22HRC limit recommended for avoiding SSC.
ISO 15156 / NACE MR0175 acknowledges this and in Table 1 List of Equipment, the drilling, well and well-servicing equipment is excluded from the standard requirements. In section -2 A.126.96.36.199 it highlights the importance of drilling fluid control by one of the following methods:
Maintenance of pH 10 or higher to neutralize H2S in the drilled formation;
use of chemical sulfide scavengers;
use of a drilling fluid in which oil is the continuous phase.
This means the corrosion is managed at the drilling rig witn controlled additions of chemicals in the drilling fluids, these drilling chemicals control the pH and scavenge H2S.
There is one case where this may not apply, drilling risers for offshore HPHT wells may have a blow out preventer on the surface, which means that in case of a kick the riser may be exposed to production fluids.