"Pigging station". I remember seeing these a lot as a kid, and I was always wondering what their function was. Finally.

Interesting section:

> There are four main uses for pigs:

> 1. Physical separation between different fluids flowing through the pipeline

> 2. Internal cleaning of pipelines

> 3. Inspection of the condition of pipeline walls (also known as an inline inspection (ILI) tool)

> 4. Capturing and recording geometric information relating to pipelines (e.g., size, position).

--

The topic interested me, so I looked around and found an article in a German newspaper [0], related to the Nordstream pipeline, it is from 2014. I asked ChatGPT to shorten and translate it because some might find the data interesting (prompt: `Shorten each paragraph to a maximum of 3 sentences and translate all to English, leave title and introduction unsummarized. Focus on the facts, numbers are important, pressures and speeds with their corresponding units as well: ...`):

--

OSTSEE-PIPELINE: Pipe Cleaner and Smart Crawler

The gas pipeline through the Baltic Sea is monitored by a special device called a "Molch" (crawler). This device inspects the pipes from the inside. The results of the measurements have now been released.

Pipeline condition must be regularly checked for sea floor changes or damage from trawling nets and anchors. External checks occur every two years using remotely-operated underwater vehicles. Steffen Paeper, responsible for inspections at Nord Stream, says the unique challenge was the pipeline's length.

The Molch was specifically developed for this task by the Rosen Group. Before deployment, it underwent extensive testing in a pipeline with a 1,153 mm diameter. Steffen Paeper stated that larger diameters could theoretically be used but are impractical with current ships.

The Molch detects early corrosion and material loss. It also checks for pipe deformations and curvature radii compliance. Although the pipes are coated with synthetic resin, the coating is absent at welding points, making them susceptible to rust.

The pipes are fitted with sacrificial anodes designed to prevent rust for at least 50 years. Nord Stream keeps a reserve of 480 pipes for any required repairs.

Wheels on the Molch measure the distance covered, enabling location-specific measurements. Mechanical devices with sensors capture the inner geometry, detecting even bumps smaller than 1 mm. These create a 3D image of the entire pipe.

The Molch uses magnetic flux sensors to detect steel corrosion and material loss. This magnetic field is calibrated to work with various wall thicknesses. It also creates a 3D image for future comparison.

Magnetic flux technology isn't new but needed adaptation for this large pipeline. Wall thicknesses range from 41 mm to 27 mm. Gas is pumped in Russia at about 220 bar but arrives in Germany at approximately 110 bar.

The Molch travels at 1.5 meters per second, powered by gas pressure, and reaches its destination in nine days. It generates about 1 TB of measurement data and operates on batteries.

The Molch is inserted and removed through locks with gate valves. It's 6.6 meters long and weighs over 7.3 tons. The worst-case scenario is getting stuck inside the pipeline.

Before the smart Molch's deployment, smaller, simpler versions are sent through. These are one-third the size and weigh 1.5 tons, helping to gauge potential obstacles.

Before inspections, a cleaning Molch removes dust and debris. It takes three to four days to reach Germany, where the collected material is analyzed.

Nord Stream is satisfied with the results. The first line had 8 kg and the second 4 kg of particles, which Steffen Paeper says is minimal given the pipeline's length. No signs of saltwater or corrosion were found. The next inspection is planned in 7 to 10 years.

---

A piece of information that went missing a bit was regarding `Wall thicknesses range from 41 mm to 27 mm. Gas is pumped in Russia at about 220 bar but arrives in Germany at approximately 110 bar.`

> In the Nord Stream pipeline, the Molch has to deal with four different wall thicknesses - from 41 millimeters of steel to 34, 31, and 27 millimeters. This is because the pressure of the gas decreases along the route.

[0] https://www.faz.net/aktuell/technik-motor/technik/die-gaspip...