Risk-based, direct assessment of network of 250 km of pipelines

08/11/2010

TWI has applied its direct assessment service to a network of 250 km of buried, non-pigable, gas and condensate pipelines in the South of Iran. The project provided a complete service to plan and perform inspection and also assessed the inspection results in terms of the pipeline fitness for continued service. The approach combined three main elements:

Risk-based inspection (RBI)
Inspection services
Fitness-for-service assessment

With the recent release, development and adoption of direct assessment standards (for example NACE) for buried pipelines, TWI put together a service to maintain and prove the integrity of pipeline networks.

Direct assessment is a four-step methodology to determine the condition of a pipeline. The methodology assessed the threat from external and internal corrosion and stress corrosion cracking for both the liquid- and gas-carrying lines. The direct assessment approach used can be summarised as consisting of the following general steps:

Phase 1 – Pre-assessment (risk-based study, using TWI RISKWISE for pipelines)

Phase 2 – Indirect inspection (above-ground inspection and flow modelling

Phase 3 – Detailed examination (excavation and inspection

Phase 4 – Post assessment (fitness-for-service assessment)

The process allowed for a cost-efficient, optimised condition assessment to be performed on the entire network of 250 km of pipelines which would otherwise be uninspectable without complete excavation.

For more information, aim@twi.co.uk

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