The International Association of Oil & Gas Producers (IOGP) published an alert regarding an unexpected failure of certain kinds of strain-hardened Type 304 stainless steel bolts. The failure happened at an offshore facility during a pneumatic leak test of gas piping exiting a test separator.
The incident
A number of strain-hardened, Type 304 stainless steel bolts, (ASTM A193 B8, Class 2) failed unexpectedly at an offshore facility while a pneumatic leak test of gas piping exiting a test separator was being conducted.
Strain-hardening austenitic stainless steel nuts and bolts to increase their strength may increase their sensitivity to chloride-induced stress corrosion cracking (CISCC) and reduce their safe upper temperature limit. Other factors such as aggressive environments and increased stress may also increase susceptibility to CISCC.
Probable cause
The bolts that failed were operating at temperatures below 50°C. The failure has been attributed to chloride-induced stress corrosion cracking (CISCC).
Recommendations
– To deal with the risk of such failures, IOGP suggests that the following should be taken into account:
– Due to external threats, Type 304/304L stainless steel nuts and bolts are not recommended for use offshore or at non-cryogenic onshore coastal facilities.
– Low alloy steel bolting or corrosion resistant alloy bolts are suggested for flanged connections between CRAs (with low alloy steel bolting being preferred).
– Consider performing a desktop review to identify the number and location of Type 304/304L(B8) stainless steel nuts and bolts in hydrocarbon systems which are exposed to the marine environment and wet deluge testing. During this consider noting any reference to B8 Class 2 bolting, strain-hardened or cold worked material.
– Consider conducting a visual survey to confirm the number and location of the nuts and bolts identified through the desktop review.
– Develop a plan to replace the nuts and bolts identified above with suitable nuts and bolts. These may include low alloy steel bolting or corrosion resistant alloy (CRA) bolts for flanged connections between CRAs.
-Update each facility’s piping specification documentation to reflect the changes to the nuts and bolts which are installed on that facility.
-Arrange the disposal of all Type 304/304L nuts and bolts held in storage, both on site and off site.
