By Tim Daly
The value of a steam system is directly related to the amount of work the system can get out of the heat in the steam, and how much unused steam is left over when the work is complete. Knowing that, it is the system designer’s job to ensure that he is sizing every part of the system to be optimally efficient. It is the pipefitter’s job to ensure that all aspects of the system operate at optimum efficiency.
To design an efficient steam system, the first things that the engineer is going to consider are how much steam does the system need, and how can he maximize the work while minimizing the amount of steam generated.
For pipefitters, this translates to ensuring that the entire system remains insulated and that all trap stations are in good working order. If the steam is allowed to loose temperature unnecessarily, then more steam will need to be generated and efficiency is lost. If traps are allowing steam to pass into the condensate returns, then more steam will need to be generated to replace it and efficiency is lost. Unfortunately for many companies, the people responsible for maintaining efficiency earned their positions by getting a good college education and serving the company well in getting their products to the consumers. Not having a good background in energy related matters, they don’t understand how much money they are losing if the steam system is not running at peak efficiency, and they may not even know what peak efficiency for the steam system is.
I went to a class once concerning boiler plant operations. The instructor was a plant manager from a mid-western power company. During one segment of the training he stated that when it comes time for belt tightening for industrial facilities, the first two things the company cuts back on are training and preventative maintenance, because although the company will eventually suffer costs associated with these cuts, they are not usually felt immediately. This allows a department manager to show early cost savings, and therefore look like a hero.
At the military base where I work in Connecticut, steam pipes have been run through trenches under the streets and sidewalks. The biggest problem we’ve had is keeping the trenches dry. There have always been sump pumps installed, but too often they would get clogged with debris and stop, or electricity would be cut, or the hot water from condensate or heating water leaks would be more than the sump pumps could handle. They tried steam fired pumps for a while, but the results were no better. Recently they decided to go with a process known as direct burial. For this, they’ve basically started putting insulated pipe into the trenches, within a second pipe—on the idea of a double wall fuel tank—creating a void space. Then, instead of placing the trench covers back down, they fill the hole with sand and pave it over. The pipes come up for valve stations where lines branch off to buildings, then go right back down into the ground. Where the pipes come up, they have trap stations, steam bleed off points, and telltale vents from the void space to let the pipefitter know if a pipe is leaking underground. We have not had a problem with any of these types of installations, but the oldest of these lines less than two years old, so I can’t give a definitive assessment yet.
In wooded areas or fields, the pipes are kept above ground. As pipefitters, these are by far the parts of the system we like best. It’s easy to work on, and as long as the insulation remains intact, there are very few problems to encounter. These types of installations are not more widely used because they are somewhat ugly to look at, so while you might see this kind of installation in a strictly industrial complex, military commanders frown on looking at it. Of course you’d also need to raise the pipes above the streets to cross intersections.
Another relatively “new to me” installation practice that I’ve noticed since leaving my job in the power plant, and returning to the field, concerns wye strainers. I was always taught to install wye strainers vertically. That is so gravity will force debris caught in the strainer to drop into the leg of the wye to be removed. The new school of thought is to install the strainers with just a slight offset from completely horizontal. This is so water will not become trapped in the strainer where steam whistling over the top could pick it up, therefore potentially creating a water hammer effect downstream.
When working with steam systems, it is imperative that you remember to consider expansion and contraction. Where I work, there has also been a shift towards bellows type expansion joints and away from the piston types. Some companies frown on the piston type of expansion joints because they require upkeep in the form of occasionally repacking them, whereas the bellows types never need repacking. The piston types seem to be more rugged and do not need to be replaced as often. But, as we discussed up above, many managers seem interested in saving money immediately instead of considering the long term costs.
If you are called upon to make a repair on a steam system, remember that there will be contraction of the pipes when the system is cooled down. Ensure that you have good anchor points installed before you break any flanges or cut into the system. When your work is complete, ensure that you remove any anchors that you installed to allow for the expansion that will occur when the steam is reintroduced into that portion of the system. When installing expansion joints, ensure that all of the pipe guides are installed properly, and remember to remove the braces on new bellows type expansion joints after they are installed and before the steam is turned on.
Pipefitters working steam systems must always remember to be vigilant about their Personal Protective Equipment. Steam is hot, and steam pipes are heavy and hard. And it is possible that superheated steam leaks will be heard and not seen. Where long sleeves, long pants, safety shoes, safety glasses, hard hats, and gloves.