Hydrogen Safety Engineering Fundamentals
Hydrogen was first observed and collected by Robert Boyle in 1671 by dissolving iron in diluted hydrochloric acid. But only in 1761 Henry Cavendish discovered hydrogen and Antoine Lavoisier named it water forming — “Hydro” in Greek means “water” and “Gignomai” means “forming”.
It is the most abundant element in Universe 75% by mass and 90% by volume. Hydrogen is colourless, odourless and insipid.
Interaction with materials
Hydrogen can cause significant deterioration in mechanical properties of metals. This is known as hydrogen embrittlement. Most of the hydrogen material problems involve welds or the use of an improper material. Hydrogen is non corrosive, but many materials absorb hydrogen, especially at high temperature. Steel absorb hydrogen and result in embrittlement which leads to failure in equipment.
High Temperature Hydrogen Attack [HTHA] : a damage mechanism that results in cracking and other defects within steel . This occurs in high stress areas within piping and vessels and likely to occur to high processing temperature.
In current cases material selection in hydrogen service is highly overlooked but the importance of materials in association with hydrogen is clear from the Hydrogen embrittlement and other failure mechanism associated with hydrogen and material interaction.
Mechanical integrity challenge : Since hydrogen can diffuse through some materials. Elastomers and gasketing materials must be carefully selected for the operating pressure and temperature to ensure adequate sealing surfaces.
Human factor hazards : Unlike hydrocarbons, hydrogen is low density hence it rises to high points in confined spaces, enclosed processing equipment’s .All workers should understand the buoyant nature of hydrogen. Since it can introduce risk in areas of plant they are not accustomed to reviews. Finding ceiling mounted electrical devices that are not intrinsically safe. Also hot work permits that are issued without testing atmosphere at the high point region within equipment or enclosure. Failure to provide proper ventilation. Failure to design piping that does not have piping dead legs or high points that can form a pocket of hydrogen accumulation.
The main technical aspects of identifying hazards and managing risk includes :
1.Establish and maintain process safety information that is important to understanding the design basis of the system
2. Conduct hazard identification and risk analysis on the facility
3.Implement and maintain safety record
An example of HTHA carbon steel heat exchanger ruptured at a petroleum refinery. The cause of the equipment failure was HTHA, a damage mechanism that results in cracking and other defects within steel. Mainly occur in high processing temperature that are above 400 F.
Common mitigation that organisations leverage
Safety by design : inherent safety can be introduced into the system by limiting the volume of hydrogen inventory stored in one place and eliminating situations where it can cause an explosion
Inventory management and facility spacing: Facility must be designed with the assumption that ignition can occur to help minimize the impact of primary and secondary fires and explosion
Ventilation : Hydrogen systems are often located outdoors to avoid explosion concerns. Ventilation should be designed to maintain concentration of hydrogen 25% of the LEL and equipment should be routinely tested to ensure it is operating to the design basis.
Ignition source management : manage ignition sources via bonding, grounding and ensuring that electrical devices meet applicable hazardous area classification
Leak and flow detection system : fixed flammable gas and flame detectors are recommended for facilities that transfer and store bulk hydrogen
Human factor assessment: employees training should be provided to employees to inform about high risk potential and human factor controls that help error proof the work .
