Understanding NACE MR0175/ISO 15156-2 Requirements for Cr-Mo, Low-Alloy Steel Rams

The inquiry is regarding the title of Paragraph A.2.3.2.2 in NACE MR0175/ISO 15156-2, “Shear rams,” which permits the use of rams made from quenched and tempered, Cr-Mo, low-alloy steels up to a maximum hardness of 26 HRC provided that the composition and heat treatment are carefully controlled and supporting SSC testing is carried out. The text of this section doesn’t limit these provisions to shear rams, but the section’s title implies that only shear rams are covered by its provisions. The inquiry raises concerns about whether all Cr-Mo, low-alloy steel rams should be allowed up to 26 HRC to ensure maximum hang-off capacity and for anti-extrusion purposes, not just shear rams.

Updated NACE MR0175

An updated version of NACE MR0175 2020 states:

Rams manufactured in quenched and tempered Cr-Mo low-alloy steels (UNS G41XX0, formerly AISI 4IXX, and modifications) are acceptable if the hardness does not exceed 26 HRC. If the hardness of these alloys exceeds 22 HRC, careful attention shall be paid to chemical composition and heat treatment to ensure their SSC resistance. SSC testing, as agreed with the equipment user, shall demonstrate that the performance of the alloy meets or exceeds that of field proven material.