Session: CS-08-01 Hydrogen Effects on Material Behavior for Structural Integrity Assessment (Joint MF-2)

Paper Number: 61411

Start Time: Wednesday, July 14, 2021, 09:00 AM

61411 - Probabilistic Design Factors for Pipes Used for Hydrogen Transport 

Hydrogen transport is generally made by pipelines. This solution is preferable over transport on the road by truck for safety reasons. Pure hydrogen is transported via pipelines. The introduction of hydrogen into the existing pipeline network has been proposed as a mode of transporting renewable energy from the production site to the consumers systems such as large wind farms. If mixed with relatively low concentration about less than 5% -15% of hydrogen by volume, this solution is viable on condition that the risks associated with the use of the gas mixture in end-use devices (such as household appliances), general public safety or the sustainability and integrity of the existing network of pipelines are not significantly affected. Any introduction of a hydrogen mixture would require modifications to the design, monitoring and maintenance practices of existing networks.

durability of metallic pipes is affected when exposed to hydrogen for long periods, in particular with higher concentration hydrogen in operating at high pressure by a phenomenon so-called hydrogen embrittlement. This effect strongly depends on steel strength and must be assessed on a case-by-case basis. However, the pipe steels in transport systems are mainly made of medium resistance steels, typically API 5L X52, which are quite sensitive to embrittlement induced by hydrogen under normal operating conditions.

 Pipeline design ensures that failure occurs when the strength capacity of the pipe steel is exceeded. This consists of verifying that the membrane stress does not exceed the admissible stress define as the material strength divided by a safety factor. In codes, this approach is slightly different as the acceptable service pressure has to be lower than the value of the maximum allowable operating pressure (MAOP).  Pipe MAOP have received attention mainly in codes . 

The calculation of the MAOP is based on the so-called “boilermaker formula” which introduces a design factor f₀  given by the code.

Different values of design factor are suggested according to different location (urban, semi-urban or rural areas). These values are estimated by experts and are known to belong to deterministic approach. New trend of safety is based on an allowable probability of risk as a compromise between safety and cost.

 For pipes used for hydrogen transport, the highest value of admissible risk is a probability of occurrence of  P_r = 10^-5_.

In general, the probability of an incident and the human, economic or societal consequences of this particular incident are combined into an overall risk factor.  The risk associated with pipeline for hydrogen transport is determined using the following general equation:

Risk = Frequency of pipeline failure * probability of flow lesser than a critical value,
* probability of ignition * probability of the presence of a person * probability of lethal effects greater than a threshold value.

Probabilistic design factors for pipes used for hydrogen transport are proposed for 3 locations: urban, peri-urban and rural areas.

The used method involves a risk equation defined as the product of probability of leakage after failure, probability to have a gas flow greater than a prescribed value, probability of ignition, probability of lethal effects greater than a threshold value and probability of the presence of a person corrected by an environment factor and a risk reduction coefficient. The results obtained are less conservative than the deterministic values provided by ASME code.

Presenting Author: Pluvinage Guy UL

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