An HIC steel plate is a carbon steel plate which is tested specifically to assess the susceptibility of the material to hydrogen induced cracking, a problem which is commonly found in the oil, gas and chemical industries in what are known as wet h2s and sour service environments.
The build up of hydrogen sulfide in pressure vessel tanks found in these industries is a major concern as it leads to a condition known as hydrogen induced cracking or HIC, where the inner wall of the pressure vessel suffers from the effects of hydrogen corrosion. As pressure vessels and steel boilers operate at a different internal pressure/temperature to the ambient pressure/temperature, such cracking can cause a reduction in load bearing capacity which could cause a potentially catastrophic failure. It is therefore vitally important that procurers in the oil and gas industry have confidence in the longevity of the steel supplied for this purpose.
HIC corrosion in a steel pressure vessel should be considered a risk at hydrogen sulphide levels in excess of 3.5mbar. Where this scenario exists, the steel should therefore be tested for its resistance to the onset of hydrogen induced cracking – the performance of the steel is directly related to the quality of the material and for this reason, greater emphasis is being placed on the quality of the steel at the processing stage. Controlling the amount of hydrogen that is picked up in the processing cycle of the material will increase the longevity of the plate in situ. Ultimately, engineers in the oil and gas industry need to have a realistic view of how long the material will last.
HIC resistant steel can undergo a variety of tests which are normally specified by the customer. Commonly, an unstressed sample is exposed to a solution at ambient temperature and pressure. After a predefined period the sample is withdrawn and assessed. Such a test can provide a clear indication of the materials suitability for purpose. Tests can be carried out at the mill itself or by an independent testing house. Certification is issued with the plate to confirm the result of any test, offering full traceability.
Another variant of the HIC problem is SOHIC or stress orientated hydrogen induced cracking. This is where exposure to hydrogen sulphide can effect the stress load around the heat affected zone of welds since this is the weak point in the tank. Whether HIC or SOHIC, the need for steel to be tested for resistance to hydrogen induced cracking is critical.