When Is It Appropriate to Use A Pipeline Scraper 1

[drywall]

It is normal practice to provide scraper facilities for cross country crude and other services which will leave a residual on the pipe interior wall. However, I have also observed scraper facilities for gasoline, diesel, benzene, propane, butane, ethane and natural gas liquids. This puzzles me, for example, although gasoline will gum it also is often used as a solvent for cleaning grease covered metals. So why do we need to scrape the line?

 

[BigInch]

The ability to insert scrapers, spheres, pigs is needed for a number of reasons. If scrapers are not needed to clean the line from deposits from a vary pure product, they are typically needed to keep the line clean of other particulate contaminations native to the pipeline environment used to transport the product.

Pigs and scrapers allow the ability to clean lines of dirt and grits, flakes from corrosion, broken pieces of various equipment (cone filters, etc.) miscelaneous chemical additives (glycols and amines for gas treating, etc.), that find their way into pipelines, foreign contaminates from corrosion and reactions between the pipe surfaces and the products that can all collect at low spots in the pipeline. A very good example would be from water vapor and dust that is contained in the air that enters a large storage tank when it is emptied when the liquid within is pumped out and on into the pipeline. The water vapor and the dust (and Lord knows what else) that the air contains will form mud at the bottom of the tank when the tank cools off. The next time the tank is filled, the mud mixes with the new liquid, so when its ready for transport, all of that goes down the pipeline. After several hundred miles of pipeline a lot of the contaminate could easily settle out to make deposits inside the pipeline.

A third reason is that, as of a few years ago, it is required by US law to have the capability to insert instrumented pigs in federally regulated pipelines to examine the pipe wall for defects, so that pressure integrity of the pipelines can be demonstrated and risk from leaks to the environment and possible explosions can be minimized.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

As for when, when the line has more pressure drop than historical or models and its costing you extra in pumping or you can't meet throughput commitments.