In the springtime, facility management teams start to prepare their cooling systems to come back online; you operate a facility with a commercial steam boiler that runs for 6 months out of the year and then sits idle for 6 months. When a boiler is not required to produce heat for those extended periods of time, most facilities will take that boiler “offline” and prepare it for a time of “safe inactivity.” The process is known as “laying up the boiler,” and it is performed to not only extend the overall life of the boiler, but also to reduce downtime and maintenance costs. In some cases, proper seasonal lay-up of your boiler can mean the difference between a boiler lasting for only 10 years or lasting for more than 30. This post will cover the features and benefits of performing a DRY lay-up.
We recently covered this same topic with regard to the reasons and best ways to perform a WET boiler lay-up here in a previous post.
As we did in that post, we will again assume that you have the best water treatment company in the area and, during heating season, your water treatment company maintains your boiler water treatment levels within optimal operating ranges to effectively inhibit corrosion and prevent scale within the boiler. For seasonal boilers even the best boiler water treatment program must be supplemented to prevent corrosion during the boiler’s non-operating months.
Why do I need to lay-up my boiler anyway?
Having the best boiler water treatment program on the planet may keep dissolved oxygen out of your boiler during normal operation, but it will not do you any good when your boiler is sitting idle offline. When a boiler is taken offline 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 pitting in steel 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 could first have to make a call to a mechanical contractor to plug or replace the corroded tubes. This is often a very expensive endeavor.
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.
Should I perform a wet lay-up or a dry lay-up?
There are two primary methods of laying up a boiler – wet lay-up and dry lay-up. As you can imagine there are advantages and disadvantages to each. Aspects that you will need to consider in the selecting your choice of lay-up procedure are as follows:
- the size of the boiler
- the type of boiler
- the length of time the boiler will be offline
- the temperatures that the boiler will be subjected to while offline
- the resources that will be required to refill the boiler with treated water
- the resources that will be required to monitor the boiler while offline
Choosing the best lay-up method for your boiler is not always so apparent and it sometimes makes sense for you to consult with an experienced water treatment service provider.
A dry boiler lay-up protocol should be used if boiler will be shut down for an extended period or when there will be no foreseeable urgency to restart the boiler. This method is also preferable where the idle boiler may be exposed to subfreezing temperatures. Unlike a wet lay-up method, the dry lay-up also has a “set and forget it” component; it does not require constant monitoring, testing or circulation of the water.
DRY LAY UP PROCEDURES
This procedure is preferable for boilers out of service for extended periods of time or in locations where freezing temperatures may be expected during standby. It is generally preferable for reheaters.
- The cleaned boiler should be thoroughly dried, since any moisture left on the metal surface would cause corrosion. Precautions should be taken to preclude entry of moisture in any form from steam lines, feed lines or air.
- A moisture absorbing material, such as quicklime (2 lb. per 30 cu. ft.) or silica gel (5 lb. per 30 cu. ft. of boiler volume) may be placed on trays inside the drums to absorb moisture from the air. The manhole should be then closed and all connections on the boiler should be tightly blanked. The effectiveness of the materials for such purposes and the need for their renewal may be determined through regular boiler inspections. This should be done every three months. If there is high humidity, this should be done more frequently. If quick lime or a non-indicating silica gel is used, desiccant plates with indicating dye should be placed on each tray with the absorbing material as a quick indicator. These plates will change from cobalt blue color to pale pink if the absorbing material is exhausted and loses its effectiveness.
- Alternatively, air dried externally to the boiler may be circulated through it. The distribution should be carefully checked to be sure the air flows over all surfaces.
- In the case of a high humidity area or a boiler that has been prone to off season corrosion in the past, there is another method of dry lay-up that utilizes an oil-based boiler treatment product to coat the inside surfaces of the boiler. This dry lay-up method is a little more substantial and it does add some extra steps, however the results are usually worth it. If this method is used the oil-based corrosion inhibitor must be removed before the boiler is brought back online. This is accomplished by filling the boiler, adding caustic and performing a high alkalinity boil out to remove the oil-based lay-up product.
Once the boiler is flushed out and refilled with properly treated make-up water it can be slowly brought back up to working temperature and operated as normal.
When is appropriate to use a WET lay-up procedure?
So glad you asked! You can read all about that in the first part of this two-part series: Boiler 101: Why a Wet Seasonal Boiler Lay-Up May Be Right for You
I want to learn more about other important boiler water treatment services. What can I do?
Kudos to you! Learning more about what potential issues your steam boilers could face is always a good idea. There is a abundance of informational resources regarding steam boiler operation and boiler water treatment available all over the internet. A great place to start is our free boiler operation eBook that is available for instant download: “10 HUGE Mistakes Facilities Make in Boiler Operation and How to Avoid Them!” which you can download for free at the link below.
Lastly, if you have any specific questions or concerns regarding your facilities water treatment program, or if you have an emergency situation that needs attention right away, please feel free to contact one of our water treatment experts.
Thanks for reading!