When connecting copper pipes together for plumbing, you can use compression fittings or you can solder the joints. Both types of connections have specific uses and advantages, and the Occupational Safety and Health Administration (OSHA) regulates one of the uses.
Compressions fittings assemble easily to install into shut-off valves that supply water to sinks, toilets, refrigerators, ice makers or dishwashers. They are also easy to take apart.
Soldering joints are much more difficult. To solder pipes together or take them apart, you need to heat the fittings with a torch until they are hot enough to melt the solder.
Compression fittings work best on appliances or fixtures that will eventually be replaced. Soldered joints work best on permanent plumbing connections that may never need to be taken apart.
The stronger solder joints withstand stress, pressure and motion better than compression fittings. If a fixture or appliance will move around a lot, such as a movable dishwasher, you should not use a compression fitting.
You can use compression fittings for low pressure, non-flammable gas such as nitrogen. But if you use copper pipe for a flammable gas, you need to solder the fittings at over 537 degrees C to meet OSHA specifications.