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The operational experience within the oil, gas and process industry has shown that process equipment such as pressure vessels, piping, components and structures & pipelines encounter damage during operation phase and sometimes the damages exceed the design requirements. In this situation the continued operation of the said item is questionable. Also the regulatory authorities will not allow the damaged equipment to be operated with the known flaw without any remedial action. The most widely used design codes ASME, ANSI, API etc do not allow flaws such as cracks due to deterioration during operation. However API recommended practice 579 provides guidelines on Fitness for Service (FFS) assessments on process equipment, structures & pipeline for continued service. API 579 provides criteria to make a decision whether to continue to operate the said equipment with the known flaw detected during inspection or to repair, monitor or replace the entire equipment.
Localised pitting corrosion in a portion of pipeline. |
API 579-1/ ASME FFS-1: 2007 provides the assessment procedures for the various possible damage mechanisms as listed below.
- Assessment of existing equipment for brittle fracture
- Assessment of general metal loss
- Assessment of local metal loss
- Assessment of pitting corrosion
- Assessment of hydrogen blisters and hydrogen damage associated with HIC and SOHIC
- Assessment of weld misalignment and shell distortions
- Assessment of crack-like flaws
- Assessment of components operating in the creep range
- Assessment of fire damage
- Assessment of dents, gouges, and dent-gouge combinations
- Assessment of laminations
The assessment procedure shall be selected based on operative damage mechanisms in the component/ equipments in questions.
For each of the above assessment procedures there are different level of assessment routes namely Level 1, 2 and 3. In some cases the assessment routes are more than 3 especially for the crack-like defects.
AGT has experienced engineers in performing FFS assessments for variety of assets as per API 579-1/ ASME FFS-1: 2007.
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