Construction personnel including civil engineers, who want to know or are newly or about to be involved in a Gas Pipeline Project may find this piece of writing useful in order to have a quick panoramic understanding of the same. The on site execution of a typical Gas Pipeline project broadly includes the following steps or activities:
Preliminary survey in order to fix an approximate route for the pipeline followed by land acquisition related activities.
Establishing acquisitioned route (ROW) by surveyor and marking of the boundaries. Right of Way or ROW includes sufficient working space to facilitate all relevant activities required for laying the pipeline, including passage for movement of equipments & vehicles etc.
Clearing of acquisitioned ROW in order to facilitate smooth future activities. Accurate establishing of centre line of pipeline by putting pegs at suitable intervals & points (pegging) by surveyors as per approved drawings.
Marking of Trench & excavation of the same by excavators as per drawings/specs/safety norms etc. including stacking of excavated earth along ROW & disposal of excess at suitable locations.
Preparation of Trench bed for laying of welded pipe segments of suitable lengths including maintaining sufficient spaces at points where these pipe segments would be welded inside the trench & also laying of approved bedding material layer.
Stringing of pipes along the trench including adequate supporting & stringing log documents.
Bending of high-radius bends by pipe bending machine at construction site. These bends are required at points where the pipeline changes direction gradually. For abrupt or steep change of direction Low Radius(LR) bends are required which generally manufactured in factories.
Grinding of pipe ends in order to make it ready for welding followed by welding fit-up as per specs for ensuing welding activities. Welded joints are thoroughly checked for defects by welding experts.
Laying of welded pipeline segments in the trench using equipments like Hydra. Generally the lengths of these segments are limited keeping in view of laying convenience & other technicalities.
Holiday Testing for pre-coated pipe segments laid in the trench in order to check for defects in coating. A common coating adopted for gas pipelines is multi layered Poly Ethelene(PE) coating carefully done in factories. Defects in coating are immediately taken care of.
Welding of joints of already laid pipeline segments in the trench and coating & Holiday Testing for the same.
Hydro Testing of laid pipeline segment. This is done to check for any leaks etc. Laying of top bedding layers of suitable materials as per spec.
Backfilling of Trench over bedding layer including compaction in layers as per specification.
There are also other construction related work in various pipeline stations e.g. IP (Intermediate Pigging) Stations, Pumping Stations etc. which proceed simultaneously.
Pigging of the laid pipeline between Pigging Stations in order to clear the inside of pipeline from possible debris. This is generally a pre-commissioning activity.
Inspection of placing of various markers/signposts along the pipeline/ROW after completion of backfilling in all respect & making the ROW ready for commissioning purpose.
Note: There are also many other ancillary activities within or outside execution site. The above article is meant for a brief idea about some of the salient construction activities on such a project. Some activities could vary from project to project in minor ways. Many of these activities are similar for several other types of pipeline.