Construction of the Pipeline Part of the System of Transit Gas Pipelines

The northern SGT gas pipeline has been built basing on administrative decisions on construction permit issued to the Investor and covering the DN1400 pipeline with its process infrastructure and a fibre optic cable in a HDPE protective tubing.

The design of work organisation envisioned occupying a 36m wide right-of way in agricultural areas (subject to reclamation) and 26 m wide alignment in forest areas where 8 m wide deforested strip was left directly over the buried pipeline. Archaeological exploration was conducted within the pipeline right-of-way before the construction commencement.

The scope of the construction and assembly work within the pipeline part of SGT was as follows:

• Preparatory operations : Staking of the pipeline centreline, topsoil removal, trees and brushwood clearing, area check for unexploded ordnance, construction of the access and assembly roads, and pipe stringing.
• Welding : Cutting and bevelling the pipes, curves bending, welding (various welding methods were used - traditional manual welding with cellulose and alkaline electrodes, semi-automatic and automatic MIG welding).
• Weld control: 100 % welds were subject to ultrasonic inspection (manual or using the Rotoscan automatic inspection system) while warranted welds and other particularly important ones (on terrain obstacles and river crossings as well in built-up areas (approx. 30% of all welds) were additionally X-ray inspected
• Weld insulation and insulation airtightness check by means of a spark flaw detector (poroscope).
• Earthwork and assembly of pipeline sections :Terrain dewatering, pipeline trench digging, laying the pipeline on the trench bottom, welding the pipeline sections together and placing the inserts, pipeline stabilisation in wetlands by installation of concrete saddle-shaped weights, installation of cathodic protection elements on the pipeline, laying the fibre cable protective tubing, as-built survey, backfilling and restoring the original ground surface profile.
• Terrain obstacle crossing : Transport facilities (roads and railway lines) were crossed in agreement with a facility owner by means of either the open-cut or trenchless pipe jacking/boring method, usually in DN1700 casing pipe; water bodies were crossed by means of the open-cut method, building by-pass channels and cofferdams upstream and downstream of the crossing; next the banks of the water body were rebuilt and strengthened.
• Crossing of large rivers : Two crossings (of the Warta and Skrwa rivers) were made by means of micro-tunnels under the river’s bed; other crossings used an open trench in the river’s bed. Then a section of the pipeline, welded together on the bank and loaded with a continuous concrete jacket (so called siphon) was pulled across the river (on the Noteć River crossing in the Pakość Lake area the siphon was put on supports attached to stilts driven into the river’s bottom); all crossings (except that on the Skrwa River) were made as two-line ones.
• Process assemblies (ZZU i ZPT) :Assembly of the armature including the basic shut-off armature, i.e. ball valves with electro-hydraulic drive, equipped with the line-break system for remote control; installation of process piping, power supply; AKPiA (Control and Measurement Instruments and Automation) containers for remote control; area development (sites, roads and fencing).
• Cathodic protection : This is a system of active pipeline anti-corrosion protection provided by means of cathodic polarisation with electric current from external sources in areas of insulation defects and loss; the cathodic protection installation is equipped with measurement points along the pipeline, monoblocks for electric separation of the pipeline parts covered by the protection and seven stations with anodic earthing devices; process and input piping (so called shleyfs) of the compressor stations and their connecting assemblies have a separate cathodic protection installation connected with compressor station protective installation.
• Hydraulic tests :Buried and pre-cleaned stretches of the pipeline underwent hydraulic testing (stress testing) consisting in increasing the pressure inside several times to generate in the pipe wall stresses higher by approx. 10% than the pipe material’s yield point (an additional effect of this test is a reduction of the level of stress remaining in the pipe after welding); airtightness test consisting in a 24-hour maintaining inside the pipe a pressure lower than that of the pressure test; pumping the water out, connection of pipe joints, dewatering by means of foam pigs, cleaning with magnetic pigs and check of as-built pipeline geometry with the Calscan calibration pigs; drying the pipeline to the dew point temperature -20 ° C.
• Technical acceptance : Technical acceptance consisting in verification of the as-built documentation of the assembly operations and tests of the pipeline stretch together with the acceptance of mechanical start-up of the shut-off armature drives; the technical acceptance was designed to release a stretch of the pipeline for start-up and filling with natural gas.
• Finishing operations: Rebuilding of land reclamation facilities, marking the pipeline route, topsoil spreading and rehabilitation, rehabilitation of the construction right-of-way in forests, removal of temporary construction site camp facilities including reconstruction of access roads.
• Final acceptance : Conducted for particular project’s tasks and sub-tasks representing a stretch of the pipeline, separated by a separate contract with the contractor.