Cleaning
Cleaning of the Pipelines is of utmost importance during Pipeline pre-commissioning in order to remove mill scales and construction debris. Pipeline cleaning is achieved by Running a series of brush pigs from the Launcher to the Receiver. Pipeline material and Internal coating determines the type of bristles on the brush pigs.
Gauging
Gauge pigs are run to confirm mechanical integrity of a pipeline at various stages of construction. A gauge pig is a bidirectional disc pig fitted with an aluminium or steel plate of 6-10 mm thick that deforms when it comes across an obstruction in the pipeline that is not within tolerance. The diameter of the gauge plate is a predetermined size to considering variance tolerances, this is usually 90-97% of the Pipeline ID
Flooding
The pipeline must be filled with filtered and chemically treated water before the pipeline can be Hydrotested, untreated water may be permitted based on how long the water would remain in the pipeline. flooding achieved by propelling batch pigs from one end of the test section to the other with the hydrotest medium which is usually chemically treated/untreated filtered water.
Hydrotest
Hydrotesting Includes pressurization of pipelines above the design pressure and holding the pressure for the specified period of time. Hydrotest consists of a strength test and a leak test. These tests either combined, or conducted separately based on the construction schedule. air content calculations are performed during pressurization to ensure the air in the flooding water is ≤ 0.2%
Dewatering
After the pressure test, the test section need to be bulk dewatered in order to prepare for drying. Dewatering is usually achieved by a train of pigs propelled through the pipeline by air, nitrogen, or product.
Drying
Most of the Hydrocarbon pipelines require drying to a specified dewpoint post Dewatering. Pipeline drying is carried out in order to prevent corrosion, contamination of equipment, enhance export product quality. Drying of pipelines also minimises possibility of hydrate formation during gas in.
Inerting
The Pipelines require to be purged with Nitrogen gas prior to introduction of hydrocarbons. Purpose of nitrogen purging is to achieve oxygen levels down to 2-5%. Different combination of equipment are available for Inerting , these include Nitrogen gas quads, liquid nitrogen supplied in tanks, ambient vaporizers, high pressure nitrogen converters, membrane units etc.. type of equipment is chosen based on the length, size, volume and location of the pipeline.
Caliper Survey
During Pre-commissioning Caliper survey is usually carried out after Hydrotest either combined with dewatering or separately post dewatering.
Caliper-Tool is an intelligent inspection system which serves to measure diameter reductions in pipelines – such as dents, ovalities, girth welds, and wall thickness changes – and to detect T-pieces, valves, and other installations. The basic body is the central mechanical element of the Caliper-Tool. All other components are fixed to the basic body.
Pipeline Chemical Cleaning
Gas export pipelines require very high degree of cleanliness to ensure quality of the product being exported. surfactant and or gel cleaning are carried out in addition to mechanical cleaning to achieve the required level of cleanliness.
Surfactant and gel cleaning can be carried out during pre-commissioning and while the pipeline is in operation. Pig trains consisting of brush and batch pigs with slugs of surfactant/gel in between them are propelled from one end of the pipeline to the other to complete cleaning.
Generally hydrocarbon based surfactants are used for pre-commissioning cleaning and cleaning of live pipelines, water based gels are generally used for cleaning during pre-commissioning, and hydrocarbon based gels are used for cleaning of operational pipelines.
Sygma engineers analyse the potential accumulated debris in the pipeline, debris loading capability of the proposed gel , size and length of the pipelines etc..