Chloride-induced stress corrosion cracking (CISCC) of strain-hardened type 304 stainless steel bolts
A number of strain-hardened, Type 304 stainless steel bolts, (ASTM A193 B8, Class 2) failed unexpectedly at an offshore facility during a pneumatic leak test of gas piping exiting a test separator. The bolts that failed were operating at temperatures below 50°C. The failure has been attributed to chloride-induced stress corrosion cracking (CISCC).
Strain-hardening austenitic stainless steel nuts and bolts to increase their strength may increase their sensitivity to CISCC and reduce their safe upper temperature limit. Other factors such as aggressive environments (e.g. offshore and coastal facilities and areas exposed to wet deluge testing) and increased stress / strain may also increase susceptibility to CISCC.
The intent of this Externally Shared Learning is to help mitigate the risk of such failures occurring elsewhere in new or existing facilities by highlighting the following, for consideration:
- Due to external threats, Type 304/304L stainless steel nuts and bolts are typically not recommended for use offshore or at non-cryogenic onshore coastal facilities.
- Low alloy steel bolting or corrosion resistant alloy (CRA) bolts are suggested for flanged connections between CRAs (with low alloy steel bolting being preferred)
Corrective actions and recommendations
- What might you want to consider?
Desk Top Review Consider undertaking 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 / coastal environment and / or wet deluge testing. During this consider noting any reference to B8 Class 2 bolting, (ASTM A193 B8 Class 2, or ASTM A320 Class 2), strain-hardened or cold worked material.
- Visual Survey Consider conducting a visual survey to confirm the number and location of the nuts and bolts identified through the desktop review.
- Replacement Plan Consider developing a prioritized 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 Piping Specification Documentation Consider updating each facility’s piping specification documentation to reflect the changes to the nuts and bolts which are installed on that facility.
- Dispose of Inventory Consider arranging for the disposal of all Type 304/304L nuts and bolts held in storage, both on site and off site
Safety alert number: 297
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