Jan 2014
Gas Distribution
Study of crater formation threshold during gas leakage on high pressure pipes
Jan 2014
Feb 2016
National Grid Gas Distribution and National Grid Gas Transmission
Neil Jackson – National Grid Gas Distribution Project Manager
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Network Innovation Allowance
The main objective is to develop and to validate a method and model to determine the limit between crater formation (that leads to a gas release into air with well known consequences) and gas migration in soils for gas transmission pipelines. The JIP partners are looking to develop learning in order to have a realistic model for the scenario of small leak on a high pressure pipe.

Experimental tests will be performed in order to collect data to develop and validate adequate models to determine this criterion. A two phase programme is planned. Phase 1 will involve a review of existing knowledge, followed by a series of large scale experiments to address the gaps in knowledge. Phase 2 will involve the development and validation of a mathematical model to determine the relationship between crater formation and gas migration for different soil types and pipeline parameters.

Tests will be performed with high pressure natural gas and hydrogen.

Experimental parameters for the characteristics are:

  • Release diameter: 5 and 12 mm (to be representative of corrosion leaks)

  • Release direction: upwards, downwards, horizontally

  • Release pressure: 16, 40, 70 and 100 bar gauge.

If during the experiments it appears useful for the project partners to test another release diameter, it will be possible to test one less than 12 mm after checking that this release diameter have a compatible burst disk.

Experimental parameters for the ground characteristics are:

  • Ground nature: clay, sand

  • Ground compactness: q4 density

  • Gas: methane, hydrogen

A video from above and sideways at ground level will be taken and based on the experimental results, analytical models will be developed in order to:

  • Respect the main geomechanical models,

  • Determine the main criteria for crater formation according to the various parameters (soil characteristics, pressure, size and orientation of leak).

  • Quantify dispersion of gas in the soil (1D spherical or linear geometries).

To develop and validate a methodology and a model in order to determine the limit between crater formation and dispersion of gas in soil for high pressure pipes.

The experimental work will be able to identify the conditions (pressure and leak sizes) under which gas soil migration rather than crater behaviour would occur. This would result in the development of a model that could be used to predict future behaviour.