TGC Engineers (TGCE) was asked to support a project to replace the regenerator quench tee at Valero Energy’s refinery in Corpus Christi, Texas, in 2001 and again in October 2012. The carbon steel, 84-inch refractory-lined tee’s operating temperature is 1,400 F. In the 2001 replacement, thermal stresses in the quench tee were causing the tee to fail prematurely. Over a 24-month period, Valero spent more than $2 million to weld strong backs and repair stress cracks in the overstressed tee to avoid a premature shutdown (see close up of overstressed quench tee).
TGCE’s first task was to survey the overstressed quench tee and associated piping. The measurement of this collection of large bore dimensionally complex piping and equipment 160 feet above grade was beyond the range and precision limits of traditional measurement technology such as laser scans. The quench ring, the dropouts to the reactor, the expansion joint and the piping to the third-stage separator were dimensionally captured using TGCE’s proprietary Advanced Integrated Measurement System (AIMS). A precise 3-D model of the tee and piping was generated to facilitate fabrication and installation of the new components. TGCE then used Caesar II for a pipe stress analysis to adjust/reduce the 1,400 F model to ambient temperature for precise fabrication dimensions (see 3-D model of quench tee).
Prior to TGCE’s involvement, Valero procured a replacement tee. TGCE modeled the new replacement tee to check for a fit with the quench ring and third-stage separator piping. This analysis revealed the new tee had the same dimensional problems as the current tee. Adjustments in the tee’s connection to the quench ring were required to accommodate the misalignments present in the new tee.
However, due to the combination of large bore piping, difficult geometries and odd angles, a precise fit-up of the replacement piping was not possible. Because shop tolerances could not provide a perfect fit, TGCE predicted the misclosures at every connection. Caesar II pipe stress analysis confirmed the cold spring introduced by these misclosures would not exceed code allowable pipe stresses for the system.
TGCE worked with the field contractor to lay out the cutline on the quench ring, reactor dropouts and connection to the third-stage separator to ensure all connections would fit-up without additional cutting and welding. The lift and weld out of the replacement components confirmed the model had accurately predicted the alignment at every connection for a relaxed fit.
The Valero maintenance manager reported this work process reduced the installation time for this element by at least two shifts. He was impressed by the precision of TGCE’s work process and its ability to remove the dimensional uncertainty from the project.
“We used TGC Engineers to verify the dimensions of a very intricate 7-foot diameter piping system 160 feet in the air, and then used the measurements to develop the newly fabricated replacement piece,” he said. “The pieces interchanged perfectly!
“Using TGCE’s techniques can save major revenue and heartache by knowing any and all replacement equipment and piping will fit correctly the first time. I can’t say enough about this technology.”
For more information, visit www.tgcengineers.com or call (713) 477-8682.
