Inspection is a critical aspect of pipeline integrity and corrosion management, since it determines the condition which defines fitness for purpose, remaining life, repair and rehabilitation programmes, cleaning regimes and inhibition programmes.
Over the line surveys
Over the line surveys are used to determine the position of the pipeline, the extent of protect the pipe is receiving from burial, its coating and CP system. Techniques include:
- CIPS surveys;
- DCVG surveys;
- Electromagnetic surveys;
- ACVG survey;
- Soil studies;
- Resistivity surveys;
- Depth of cover;
- Sub-Meter GPS locating.
Pipeline inspection or pigging is an expensive operation which can present significant risks. It is also complex in that it presents the operator with a number of problems:
- Variety & Technology – there are a large number of vendors and there are various technologies (MFL, ultrasonics, etc.);
- The pipeline and the pig – correct pig traps are needed, and there must be no obstructions (e.g. reduced bore valves or tight bends);
- Cleanliness – the pipeline will need to be clean to ensure good results from the pig;
- Running the pig –conditions such as flow rate, temperature, pressure and composition must be suitable for the pig run;
- Optimising runs – an operator needs to know which of his/her lines to inspect first, and what level of data recording is needed.
The decision to pig, and in particular to inspect, a pipeline is a major stage in the maintenance and integrity management of a pipeline. A step by step process of evaluation, preparation and management is required when preparing and undertaking such projects. Penspen Integrity has a wide range of highly experienced specialists with knowledge covering the whole range of planning and operations for pigging.
Some pipelines are not conventionally piggable due to not having pig traps fitted, only a single end access such as with loading lines or lateral connections, too lower flow rates, mitred bends, small radius bends or back to back bends. The strategy here is to make it piggable or consider other technologies including tethered tools or use direct assessment. Penspen has considerable experience of unconventional pigging methods/technologies.
Direct assessment can be External Corrosion Direct Assessment (ECDA) or Internal Corrosion Direct Assessment (ICDA). Direct assessment is a structured process used as an alternative to pigging it is performed in four stages:
- Pre-Assessment – Collection and evaluation of historical data and pipeline characteristics;
- Indirect Inspection – Use of over the line survey techniques or internal flow and slope assessment to determine high risk areas for excavation;
- Direct Examination – Excavation and inspection;
- Assessment – Assessment of defects and definition of repair and inspection plans.
- Over the line surveys;
- Direct assessment;
- Review of pipeline suitability for pigging or piggability survey;
- Assessment of “unpiggable” pipelines;
- Review and assessment of pipeline cleaning including type of pigs and running sequence needs based on history or likely debris and contamination;
- Preparation of cleaning and inspection procedures;
- Project management including coordination, planning and site supervision of pipeline cleaning and gauging and inspection operations;
- Training of Pipeline engineers and technicians;
- Selection of inspection technology based on likely degradation and inspection objectives;
- Design of pig launching and receiving facilities;
- Design of temporary filtration for debris collection;
- Provision of pigging technicians;
- Full turnkey inspection services.