Cathodic Corrosion Protection Of High Strength Subsea Bolting

The selection, specification, manufacture and installation of fasteners for subsea use is critical to ensure their resistance to corrosion due to various forms of environmentally assisted cracking.

As Oil exploration progresses into far deeper waters, the cost of a fastener failure or other mechanical component breakdown is both a serious financial risk but more so the environmental damage could be truly catastrophic.

With reputation at stake, Hague Fasteners with 45 years of sector experience and technical excellence ensures your subsea projects are without risk and quality assured.

The Subsea specifications Hague Fasteners work strictly too give particular emphasis on the prevention of environmentally induced cracking under the conditions of cathodic prevention. Cathodic protection is frequently used in Marine vessels, and offshore and subsea steel structures to reduce the base metal corrosion by making it the cathode in an electrochemical cell.

It is HagueÂ’s decades of experience and knowhow that gives their ever growing Subsea customer base the peace of mind that the special fasteners manufactured and coated by Hague Fasteners do not deviate from the expert specifications designed to minimise the risk from the various forms of environmentally assisted cracking (EAC).

These include stress corrosion cracking (SCC), hydrogen embrittlement (HE) and sustained load cracking (SLC).

The sectors supplied by Hague Fasteners are almost always the high performance applications requiring higher strength fasteners. A major issue with fasteners used offshore and subsea is that higher strength fasteners are susceptible to stress corrosion cracking and hydrogen embrittlement. In general, higher the strength, the higher the hardness of the material and the greater the susceptibility to these failure mechanisms.

The more common critical offshore and subsea bolting material grades requested are the common bolting materials ASTM A 320 Grade L43, ASTM A320 L7 and ASTM A193 Grade B7, the fastener industry is flooded with inferior imported mass produced petrochemical fasteners where quality is often compromised in exchange for being the cheapest and securing contracts. Hague Fasteners distance themselves from this side of the market as failures in these cheap and suspect quality items have occurred, particularly where the use of cathodic protection increases their susceptibility to hydrogen cracking.

Hague Fasteners certify their manufactured items with additional PMI testing, MPI testing and further ensure integrity of their components by limiting the hardness well below the proven 34 HRC where high strength bolting becomes highly susceptible to cracking from hydrogen embrittlement induced by cathodic protection. For reference, the maximum hardness of regular B7 is 35 HRC and hence can fall above the susceptible range.