When Spring arrives, it is time to consider how your boiler system will spend the next few months while it sits dormant offline. If you own and/or operate a facility with a commercial steam boiler that only gets seasonal use, then this topic is for you.

When a boiler is not required to produce heat for extended periods of time, it often makes sense to take that boiler “offline” and prepare for a time of “safe inactivity.” The process is known as “laying up the boiler.”  The main reason for doing this is to extend the overall life of the boiler and reduce maintenance costs and downtime. In some cases, proper end of season lay-up can mean the difference between a boiler lasting 10 years or lasting for more than 30. This post covers the features and benefits of performing a WET lay-up. (The next post in this series will cover a DRY boiler lay-up procedure.) The wet lay-up protocol is the one that you want to use if you have a boiler that is sitting idle, but that may need to be ready to go online in a hurry. This is also known as a standby boiler.

For the purposes of this post we will assume that you have the best water treatment company in your area and, during heating season, your boiler water treatment levels are maintained within specific optimal operating ranges to effectively inhibit corrosion and prevent scale. However, for seasonal boilers, during the non-operating months, even the best boiler water treatment program must be supplemented to prevent corrosion.

There are two primary methods of laying up a boiler –  wet lay-up and dry lay-up. As you can guess there are benefits and potential downfalls to each. Choosing the correct method is not always obvious and so it may make sense for you to get some guidance from an experience water treatment service provider. Some factors in the selection of lay-up include the size and type of boiler, the length of time the boiler will be offline, the temperatures that the boiler will be subjected to while offline and the resources needed to refill and monitor the boiler with treated water.

Why do I need to lay-up my boiler anyway?

When a boiler is taken off-line and allowed to cool down for extended periods of time, a boiler lay-up program is highly recommended, to offset the increased levels of oxygen in the boiler. Oxygen can quickly produce pits in tube sheets and boiler tubes. Once oxygen pitting starts, it can easily corrode through a boiler tube in a very short period of time. When it is time to start your boiler back up in the fall, you first have to make a call to a mechanical contractor to plug or replace tubes. Not good for your boiler and very expensive.

What do I need to do when my boiler is taken offline?

When a boiler is taken out of service, the boiler should be cooled until the water is below the atmospheric boiling point, but not below 180°F, and then the boiler should be emptied and flushed out. An inspection should be made to determine what repair work is necessary and what cleaning should be done. A decision should then be made on whether to employ dry or wet storage techniques.

Wet Lay-up Procedures

A wet procedure may be used for a boiler that is taken offline completely or for one that has been placed in a “standby” condition. Wet storage is particularly useful if the standby boiler may be required to go back online at short notice or if it is impractical to employ a dry storage procedure. The method is not generally employed for reheaters or for boilers which may be subjected to freezing or sub-freezing temperatures.

There are a few alternative procedures that may be employed in a wet lay-up. The following is the most typical:

The clean empty boiler should be closed and filled to the top with water that has been conditioned chemically to minimize corrosion during standby. It is important that water pressure greater than atmospheric pressure should be maintained within the boiler during the storage period. A head tank may be connected to the highest vent of the boiler to help maintain pressure above that of the atmosphere.