Stack Replacement

Last Year we inspected a stack that was in horrible shape.  We recommended the entire stack be taken down and replaced.  A year later our customer called us and said they were ready to replace the stack, however they have only 7 days in their shutdown schedule to tear down the old stack and erect the new one.  This normally isn't an unusual amount of time, however this particular location was still getting snow and during the site visit experienced 60+ MPH winds.  Infact, during the previous year the wind ranged from 23 to 57 mph.  How was a 300' tall crane going to lift the sections of the stack in and out, each section was about 50' long and approx 15,000 lbs.  The wind load alone would cause a drag effecient of more than the crane's lifting capacity of 27,000lbs. 

To make matters worse the stack is surrounded by a steel derrick that supports the stack.  There is less than 2 inches of clearance around the stack.  Lifting the old stack out and placing the new one into the derrick would need to be completed with the utmost precision.  Upon inital rigging of the old stack it was discovered the cracks in the stack had deteriorated to the point where they covered 270 degrees of the stack.  When we lifted the stack it opened up like a soup can...




Can you locate all four workers on the derrick?

 

After significant amounts of engineering we came up with a solution that would allow each of the pieces to be lifted out of the tight fitting derrick safety.  This project invloved a great deal of risk from lifting to pinch points to technicians needing to be on the derrick to guide the stack in and out.  Each step of the project required a great deal of planning to midigate the risk as much as possible. 

In the end the replacement went off with out a hitch (minus some down time due to excessive wind).  We also up sold the customer on some additional stack components and were asked to come back the following year to inspect 4 more stacks they have.  In the end the 45 days of planning, engineering, ordering the necessary tools for the job and building the new stack were all worth while as the customer was very happy.