Head/shell Joint Steam Leak
Steam leaks in the head/shell joints of Yankee dryers present a continuous challenge to those responsible for the safe operation of the dryers. If allowed to continue, such leaks can result in serious damage to the joint and lead to condensate "spitting" on the sheet or compromise the integrity of the cylinder. The most common means of sealing these joint leaks is pumping the joint with sealant under very high pressure. Determining precisely where to pump the sealant is difficult and is often done with a mirror held to the joint while the dryer is run slowly under steam pressure. Unfortunately, due to joint flexibility and the differences between sheet-on and sheet-off thermal and stress conditions on the Yankee dryer, the locations of leaks seen under sheet-off conditions may not match the locations of the leaks when the dryer is making paper. It is possible to expend considerable time and energy pumping joints in areas which do not leak under papermaking operation.

As illustrated in Example 3, PROdry's high-speed thermal imaging can be used to accurately locate steam leaks at the head/shell joint and around the bolt circle under papermaking conditions. The checks can be made while maintaining production, without stopping the paper machine. The thermal strip shown at the right of the example figure covers the region of the head/shell joint, synchronized for one revolution of the Yankee dryer. The Yankee was running 3550 feet/minute under 109 psig steam pressure at the time the image was captured. The use of high-speed, precision infrared imaging allows even small details of the area to be clearly visible. An enlarged view of the area around the manhole is shown to the left of the strip. The bolt heads can each be clearly seen as cooler lines to the immediate right of the manhole. The larger spots to the left of the manhole are the Yankee journal bolts.

A head/shell joint steam leak is indicated by the gray square near the bottom of the strip. An enlarged view of the area is shown at the left of the image. Since this leak was weeping condensate, it appears to be cooler than the surrounding metal due to evaporative cooling. Live, blowing steam leaks usually appear hotter than the surroundings. The leak can be positively located by simply counting the head bolts starting at the manhole. With this precision data, the mill was able to concentrate their efforts on pumping near the running leak and the dryer was sealed.

	Example 3: Yankee head/shell joint temperature map showing steam leak through the joint ("Ironbow" palette).
Click to enlarge

© 2007 PROdry Technology, Inc. Site last updated 3/7/07