Expansion Joint Heating System 1

[jdav]

The community I work for hired a consultant several years ago to evaluate the condition of an existing aerial river crossing. The crossing itself is insulated 36" steel pipe that was found to be in excellent condition via ultrasonic thickness measurements taken along its length.

The water main runs parallel to a local bridge and is supported on the north and south ends with abutment structures and in the center with a pier in the river. The north abutment has a chamber within it that contains a stainless steel, toroidal design, expansion joint for thermal expansion and contraction. The joint is then contained within a fabricated enclosure (16 gauge sheet metal insulated with glass wool) that is heated via two 250 watt strip heaters. The strip heaters are controlled by means of a thermostat in the bellows of the expansion joint.

During the consultant's evaluation it was noted that the legs on the expansion joint enclosure had completely deteriorated and the structure now is supported solely by the water main. Additionally, deterioration of the enclosure now subjects the expansion joint to exposure. The report prepared by the consultant recommended replacing the enclosure and heating system.

I would like to know if the heating system is really necessary. The report states that the enclosure was installed to provide a controlled environment around the expansion joint, thereby extending its useful life. However, I have not encountered any enclosures like this previously, nor has the mechanical contractor that I have discussed this project with. I also spoke with one current expansion joint manufacturer and they stated this is not their current practice for similar installations. While this installation is in an area subject to cold temperatures (Michigan), the temperature of the water seems like it should largely control the thermal variations. This is a main trunkline and as such sees consistent flow, minimizing external temperature impacts.

Does anyone have any experience with expansion joint heating systems like this? Is this a current recommended practice or just something dreamed up by the old designer (pipe was installed in 1955)?

 

[bimr]

Is it possible that the heat was applied to prevent condensation on cold surfaces?

Specifying sufficient insulation thickness with a good vapor retarder is the most effective means of controlling condensation and limiting corrosion on cold piping, ducts, chillers and roof drains. Sufficient thickness is needed to keep the surface temperature above the dewpoint temperature of the ambient air.

 

[jdav]

Thanks bimr. That's a good point.

I hadn't considered condensation but you may be on to something there. At this point its difficult to know what the design intent was since it was designed and installed in the mid 50's.

 

[greggy]

Being an employee at a water utility in northern Ohio and having to maintain expansion joints on water lines hanging beneath bridges prone to freezing, I can vouch that a heated expansion joint is a nice thing to have to prevent the sliding joint from freezing solid to where it won't work.

This past winter we had a 24 inch diameter expansion joint freeze while temperatures stayed about 15 degrees for four days. The pipeline had contracted just enough where instead of the expansion joint moving, the shrinkage pulled the next coupled joint apart and was a big mess, and the whole thing was expensive to replace and repair.

Regular expansion joint inspection and maintenance is recommended.