In most cases, pipe scale is the material that builds up on the inside of pipes. This material makes the inner area of the pipe smaller, which will either decrease the volume or increase the pressure of the liquid flowing through the system. In addition, this makes machinery based on flowing water work harder to gain the amount of liquid they need. Pipe scale is also the term used to describe the musical resonance of a specific pipe on a pipe organ.
Pipe scale mostly consists of minerals present in the liquid flowing through the pipe. In water, this generally means calcium and magnesium. As water flows, small irregularities in the pipe's surface will catch impurities. These impurities will continue to catch on these rough spots, causing them to grow. This is similar to how the formations in caves are made, just much faster.
The buildup of pipe scale has several direct impacts on the liquid in the pipe. As the inner surface of the pipe becomes smaller, the liquid must change its flow patterns to compensate. If the system allows for quantity variations, the volume of water transferred by the system will begin to decrease. If the system transfers a set volume of liquid, then the pressure and speed will build up in the pipe. This could cause problems if there are weak or leaky joints in the system.
This change in the flow of the liquid may cause problems for systems that rely on it. Systems that use water, like dishwashers or boilers, will need to work harder to get the requisite amount of water they need. This results in more pumping time for the appliance, which ultimately means more electricity used. Non-water systems may have more trouble. If the liquid is a coolant or lubricant, then the flow changes could cause a catastrophic failure of the attached device.
There are several indirect results of pipe scale as well. Longer drain time for sinks and bathtubs allow bacteria and grime to build up. The scale makes the flowing liquid more mineral-rich, which prevents soap from lathering and changes the flavor of drinking water. This also moves the minerals into the attached systems, shortening the lives of attached devices.
When pipe scale refers to music, it is the ratio of the pipes length to diameter. In general, longer pipes are low tones and short pipes are higher-pitched. Changing the width of the pipe allows some pipes to be shorter or longer without changing the tone.