When preparing specifications for weathering steel transmission pole projects, utilities will often require that the poles be hermetically sealed. This means that the inside of the poles are sealed from the outside environment through welding. The rationale behind this requirement is easy to see. Weathering steel requires a number of wet/dry cycles in order to form the protective oxide coating that prevents further corrosion. If water is allowed to rest against a weathering steel surface, this oxide coating cannot form and corrosion can be a result. By eliminating water from inside the pole, this corrosion mechanism is eliminated. The most common method of hermetically sealing steel poles is through the use of sealer plates that the top and bottom of a slip jointed section.
Problem: Difficult slip joint fit up on hermetically sealed poles
Sealer plates are often used on weathering steel slip jointed poles to provide a barrier against air intrusion. A sealer plate is placed at the very top of the lower section while a second sealer plate is placed above the point of maximum slip on the upper section. These sealer plates can significantly stiffen the sections against deformation. Often, steel pole sections will not be perfectly round when formed. In order for the two sections to mate together properly, the sections need to conform to each other. When sealer plates are present, the tubes are stiffened against deformation which can make it difficult to achieve the proper slip length.
Solution: Eliminate the upper section sealer plate
If the top of a section is sealed against moisture there is no way for moisture to travel up the slip joint. Furthermore, the air gap between the top and bottom section allows any condensation or other moisture that finds its way inside the tube to drain out the bottom. Following these recommendations will go a long way towards ensuring proper slip joint fit-up, as well as make the contractor's life easier.