MTBF and hydrogen

Functional safety of system components

The large-scale use of green hydrogen will become a reality for many chemical processes in the near future. The petrochemical industry is also preparing for greening with increasing use of hydrogen.

Minimize the probability of failure in the supply chain

The process chains in the growing climate-friendly hydrogen market require innovative storage technologies and efficient transportation options for green electricity. The top priority is sustainable security of supply, even with increasing use of hydrogen and reduced use of fossil fuels.

Some of the existing infrastructure - e.g. from the natural gas supply - can be used, but new hydrogen value chains must also be effectively integrated. This includes smooth interlinking between offshore structures, ports and inland supply and their greatest possible reliability in ongoing operations.

Planning and assessment of the probability of downtimes

When planning new systems or upgrading existing supply systems, planners and plant manufacturers must be able to consult reliable standardized information from component manufacturers, in addition to their own experience. Manufacturers of electrolyzers conduct a hazard and risk assessment for their systems in accordance with the HAZOP hazard analysis procedure.

The effectiveness of a system can be measured using key figures that evaluate the components in terms of their trouble-free running time. For example, if unsuitable valves are installed in a hydrogen plant, this leads to unwanted disruptions to the system function or even to a system failure/shutdown. 

Unplanned downtimes/failures can be reduced to a minimum by a customized layout of the system with the best possible interaction of all components and the associated consideration of the expected downtimes. Various acronyms and abbreviations exist for the availability of technical systems, which provide information about the operating time or repair frequency of a component.

The time average value – Mean Time

Mean time values are used as key figures when evaluating the system components.

It must be taken into account whether the part in question is intended for repair in the first place. If this is not the case, the acronym MTTF (Mean Time To Failure) is used to assess it, which indicates the mean time to irreparable failure as a key figure. MTTF therefore serves as an indicator of the average service life of a component. If the component fails, it is not repaired but simply replaced.

If repair/maintenance is possible, the MTBF (Mean Time Between Failures) indicator is used. It describes the average operating time of the component, e.g. an industrial valve, between two failures, i.e. the average probability of failure. This key figure provides information about the product reliability of the valve assuming round-the-clock operation throughout the year (24/365) and its functional safety.

The higher the MTBF value, the more reliable the valve is. To determine the MTBF failure probability, the boundary conditions to which the device or system is exposed must also be taken into account, e.g. ambient temperature, number of start/stop cycles per day or compliance with the specified maintenance intervals. In addition, there are factors that cannot be influenced, such as the type of installation of the component in question.


Determining the MTBF key figure

The MTBF figure can be calculated in three ways.

For example, an analysis can be carried out on the individual components of newly developed valves. For this purpose, empirical values from commercially available databases are used, which provide information on component reliability. However, this method is very time-consuming, can only be carried out externally and is only suitable for new products.

Another way of determining the MTBF value is to evaluate complaints. This is standard practice at Mankenberg. It goes without saying that this method is only suitable for existing products or series. On the other hand, the analysis is cost-effective as it can be carried out internally with the data available at Mankenberg.

The third way to determine an MTBF figure is to analyze the system on the basis of downtimes. This analysis is not suitable for Mankenberg, as it does not consider individual industrial valves, but the entire system.

Complaint evaluation to determine the MTBF key figure

At Mankenberg, complaints are documented with various reference values. In addition to the data of the complaint case, the overview also includes details of the sales quantities per valve series and any other complaints that have occurred for this valve type in the past. The available data goes back more than 20 years to the time when the company's own ERP system was implemented.

The failure rate analysis distinguishes between four groups: dangerous and non-dangerous faults (Safe/Dangerous) as well as the possibility of detecting these faults or not (Detected/Undetected). 

In this way, a total of four different values are displayed with the Greek letter Lambda λ and a pair of letters as a symbol:

  • λSD = safe detected
  • λSU = safe undetected
  • λDD = dangerous detected
  • λDU = dangerous undetected

This is used to calculate the total failure rate (safety function) λtot device.

If you add the mean repair time MTTR (Mean Time to Repair) to the calculated figure, you get the MTBF value.

Key figures increase planning capability

Customers receive valuable information on the operating time of the valve they have purchased for their system planning. The results are issued in a form similar to a manufacturer's declaration. The customers were very satisfied with the data provided, as they were able to use it for their preventive maintenance (TPM) and minimize unplanned downtimes of their systems.

Vite, vite! Act quickly in the case of a plant shutdown

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