Award winners resolve Super Heater failure

MESNZ member Mainstream Engineering (MEL) were called to assist their client following two superheater tube leaks found during routine maintenance hydrotesting of their steam boiler. The tubes were replaced and the boiler was returned to service.

The client wanted to get to the bottom of the failure and called in MEL the supreme winner of the Eastern Bay Horizon Business Excellence Awards.

Inspection identified the crack in the tube was a fatigue type failure and without remedial action would result in a significant and on-going threat to the reliability of the boiler operation.

MEL stepped in to pinpoint the root cause of the cracking and possible solutions. The first task was to develop a 3D model of the super heater elements, local roof penetration and seal arrangement and then use their Finite Element Analysis (FEA) software to simulate various loading conditions and combinations.

The simulation results confirmed lateral movement of the super heater tubes created very localised high stress concentrations at the failure site.

Kawerau-based MEL then set about developing an appropriate solution that would fit within their client’s maintenance scheduling constraints (5-day installation window, reliability and cost effective).

Using their considerable experience in identifying failure risks and root causes which enables them to remove or mitigate the risk ensuring equipment reliability, MEL developed a solution based on ‘stay’ tubes to tie the super heater elements together across the boiler and restrict the swinging movement that caused the failure. The ‘stay’ tubes prevented lateral swinging movement but allowed for differing thermal growth.

Mainstream Engineering utilised a combination of manual thermodynamics calculations and Computerised Fluid Dynamics (CFD) software to take into consideration gaseous and solid material heat transfer, furnace gas flow and steam flow dynamics to design a steam-cooled ‘stay’ tube. The design required two ‘stay’ tube legs to ensure tube metal temperatures did not exceed material code limitations and steam outlet temperatures could be safely mixed into the headers prior to final temperature attenuation.

MEL staff then successfully managed the fabrication and installation of the ‘stay’ tube during the following annual routine maintenance shutdown.

MEL will be demonstrating their software applications and their experience in equipment and component inspections, failure analysis and troubleshooting of manufacturing equipment at the National Maintenance Engineering Conference (NMEC 2018).

NMEC 2018 will be staged in Rotorua 13- 15 November 2018. It is the 16th annual National Maintenance Engineering Conference and will bring together over 200 delegates and industry leaders to spend three days learning about today’s most pressing maintenance and reliability challenges.

FOR MORE INFORMATION ABOUT NMEC PLEASE CONTACT: BARRY ROBINSON, CHAIRMAN, MESNZ, PHONE 027 286 4722.

FOR MORE INFORMATION ABOUT MAINSTREAM ENGINEERING PLEASE CONTACT DARRIN OR WARWICK ON PHONE 07 323 9003.