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Roseville City Council Page 2 of 5 are mounted within the vessel, removing the tubes for cleaning and pressure testing is not an option.) The vessel was inspected. Chiller tubes were pres- sure tested. Thirteen leaks in chiller tubes were eventually identified; those tubes were plugged off. (Giventhe number of steel tubes in the chiller vessel, the system can successfully operate even if some tubes are plugged.) Then, last week the vessel was reassembled, recharged with brine and ammonia, and repressurized. However, the chiller vessel is still not holding pressure. We have asked Gartner to return and disassemble one end of the chiller vessel so we can see what is going on inside. This will cost approximately $9,000 to erect the scaffolding and hoists and winches necessary to access and remove the end of the vessel assembly, and to purge the vessel of brine and ammonia so we can inspect it. As this report is being written we don't know � previously plugged tubes are leaking, if entirely new leaks have developed in additional tubes, or some com- bination of the two. But, to say the least, it is disturbing that the chiller vessel is still not holding pressure. C. Staff s Concern. Our concern is this: Maybe the steel cooling tubes have reached the end of their useful life. At a cost of $80,000 we have plugged 13 tubes; yet, upon re- charging with brine and ammonia and upon system start-up even more leaks have now developed in the chiller vessel. At this cost, how long can we go on re-opening the chiller vessel and plugging leaky tubes? Perhaps the existing 800+ steel tubes have been weakened by the effects of corrosion to the point that those tubes have become brittle and fragile. If so, they will routinely de- velop more and more leaks. II. Options Staff has developed the following options for Council consideration. No final decision is necessary immediately unless the Council is comfortable doing so. However, we want to lay out the problems and some options so that Council is briefed, has an opportunity to ask questions and to suggest other options for consideration. A Retube the Existin�; Chiller Vessel at an Estimated Cost of $175,000. Rather than engage in an expensive and losing game of plugging more and more leaky tubes maybe it is time to replace all 800+ tubes within the chiller vessel. As you might imagine, these tubes are specially manufactured. It can be quite tricky getting old, corroded tubes out of the existing vessel. But there is a window in the side of building which houses the chiller vessel; this window was designed for eventual re-tubing of the chiller vessel. Thus, it was antici- pated that the chiller would have to be re-tubed, just not this soon.