Overhead pipelines are used to transport Coke Oven (CO) gas and other gases. The pipelines are 10 – 15 m above the ground. Depending on joining of the pipe segments the pipelines are classified into two types – Welded and Flanged. The total length of the Coke Oven gas network is 20 km. The maximum straight length between joints is around 200 m. The diameter of the pipeline varies from 1000 to 3200 mm. The maximum flow rate of the gas in the network is 10,000 Nm3/hr with a maximum pressure of 0.12 Bar. The pipelines are not insulated and the pipe wall thickness varies from 16 to 20 mm. The pipelines are exposed to the atmosphere and temperature of the pipelines is the ambient temperature. The pipes are made of Copper Steel while the flanges are made of Plane Carbon Steel.
The pipelines and the other supporting structures get corroded due to the presence of different chemical constituents in the gas leading to the reduction in pipe wall thickness. Condensate is formed due to the presence of impurities in gases such as Tar, Naphtha & Sulphur. Condensate from the pipelines also drips from flange joints on adjacent lines/structures due to which the supporting structures, as well as underlying utility pipelines, also gets corroded.
The condensate also degrades the performance of control valves/on-off valves resulting in frequent maintenance. Scales, both internal and external, also builds upon these pipelines, which causes further pipeline degradation and process interruptions. These scales are made up of a mixture of Naphtha and Ammonia. The problem of corrosion is pronounced in the flanges, U sections, and bends, where the gas direction changes.
Corrosion and condensate deposition affects the process parameters like pressure and flow rates. Any uncontrolled variation in the process parameters leads to disintegration or even explosion of the pipelines, which is highly undesirable and needs to be prevented at all cost. At present, any problems with the pipeline, like corrosion, blockages & sedimentation, get identified only after leakages are observed. Drain plugs are provided at many places to remove the condensate. During the maintenance, condensate is removed and pipe wall thickness is measured.
In summary, the problem to be solved/addressed is the detection of corrosion and formation of sediments and deposits inside pipelines and providing an early warning that will enable us to take necessary actions to prevent any damages to the pipeline.
Options that have been tried earlier and the corresponding issues faced are
- Manual periodical cleaning of pipelines. Issues faced: more shutdowns, high repair costs
- Gaskets/seals/rope replacement. Issues faced: low effectiveness, high downtime, leakages
- Anticorrosive treatment. Issues faced: High costs, low retention
The solution must meet the following requirements:
- Facilitate online/ advance detection/condition monitoring of the above-cited issues while the media is in service
- Enable monitoring of pipe wall thickness
- Monitor inner deposits and tapping them out, if any.
- Provide early warnings
- Provide the exact location of problems
- Must not impact any process parameters
- Self-diagnostic, reliable & easy to maintain
- Provide dashboard/map of the diagnostics and problems detected
- Low cost
Following constraints should also be considered while developing the solution:
- Shutdowns are not available
- Use of radioactive materials is not permitted
- Internal parts are not accessible for inspection
- Puncturing of pipelines is not allowed
- The solution should not necessitate maintenance of its own