Piping

1Q. What tend to be concerns in piping?

1A. Existing designs tend to have corrosion under insulation (CUI) problems in aging plants, flange leaks due to bolt loosening and gasket problems or weld cracking due to vibration, thermal upsets or poor field repair welds. Re-rates can cause temperature problems if the piping flexibility studies have not been performed. Of course there is always the probability that the wrong piping material or welding procedures have been used. New plants can have all of the above too.

2Q. What is a piping flexibility study?

2A. It's an analysis of the piping and it's connection to the various pieces of equipment. It is usually performed by a piping designer using rather sophisticated software which considers the extremes of temperatures in the design window. The idea is to keep the loads low enough so that the equipment is not overstressed. However the piping can't be so flexible that it will vibrate or sag and look like spaghetti. Too flexible and more piping is used thus a higher project cost. Too rigid a piping system and the loads are too high. It's a real juggling act to get it all correct and much experience is required to do it right.

3Q. We have a small manufacturing plant and are putting in some piping. Should we be following some design practice?

3A. It depends on the type manufacturing plant and the type piping service. Domestic water is one thing, but hydrocarbons are another. Typically ANSI B31.3 Chemicals Plant and Petroleum Refinery Piping are followed for this type service. For boilers ANSI B31.1 Power Piping is followed. The Nuclear, Refrigeration, Pipeline all have their own Codes to follow. When in doubt use a contractor familiar with your type of operation so that all national and local regulations and codes are met.

4Q. What is stratified fluid bowing in piping?

4A. When hot fluid only fills part of a pipe, a temperature difference occurs from one side to the other. This can cause the pipe to "bow" in the direction of the hotter side, and can cause higher stresses on that side of the pipe or vessel. This is not normally analyzed in a typical piping flexibility study.

5Q. What problem does a blocked-in liquid in a piping system cause?

5A. When a pipe is full of liquid and tightly blocked in at each end and the temperature of the piping and liquid increase the same amount, the liquid expands more than the steel pipe. Something has to give, so the pressure in the pipe will rise. If conditions are just right the pipe can burst.