How to Assess Hydrogen Pipeline Integrity by Applying Fracture Mechanics

Introduction

When pipelines transport hydrogen instead of natural gas, safety planning must consider the fluid being handled. That means pipeline operators must verify the service life of new or converted pipelines by applying fracture mechanics that consider the probability of the transport medium (in this case, hydrogen) causing damage. Material embrittlement induced by hydrogen could lead to sudden fractures. In cases where this is a concern, evaluations using fracture mechanics to assess the reliability and integrity of steel pipes exposed to cyclic loads are necessary.

GET H₂ is a German initiative consisting of seven companies planning to build cross-border infrastructure for green hydrogen, from production to transport and purchasing. By use of green hydrogen in refineries, steel production, and other industries, the initiative is intended to prevent emissions up to 16 million tons of CO₂ by 2030. The German government is not alone in its efforts to replace fossil energy carriers by power produced from renewable sources under its Hydrogen Strategy. Global industries and economies are likewise planning along these lines.

The establishment and development of a hydrogen economy offers various advantages compared to the expansion of the power grid. For one thing, a large part of the existing natural gas infrastructure can be used for the new form of energy; furthermore, the laying of buried pipelines is readily accepted by the public and can be realized at manageable costs. In addition, many manufacturers, installation, and operating companies have experience in working with pipeline parts and technical components as well as storage caverns. Nevertheless, safety, reliability, and maintenance practices must take the specific concerns associated with hydrogen into consideration.

Natural Gas Networks Ready for Conversion

History has shown that natural gas lines tolerate changes in the fluids they transport. When first installed, the pipeline networks transported what is known as “town gas” produced from coal. Town gas already contained a high percentage of hydrogen as well as methane, nitrogen, and carbon monoxide. In the second half of the 20th century, town gas was replaced by natural gas. Natural gas is categorized as “low calorific gas” or “high calorific gas”. The latter has a higher methane content and calorific value. As less low calorific gas is extracted, the amount of high-calorific gas fed into our gas networks is currently increasing.

Successful conversion has always depended on professional planning and implementation of the associated technical measures. In Germany, many owners and operators of gas grids can look back on over 100 years of experience – the same length of time for which some of their networks have been in operation. Now, state-of-the-art measures must be determined to ensure safe operation of the pipelines that will transport 100 percent hydrogen in the future. Pipes for cross-regional gas transport have diameters of up to 55 inches (1,400 mm) and are operated at pressures of up to 1,450 psi (100 bar).