Award win­ners re­solve Su­per Heater fail­ure

DEMM Engineering & Manufacturing - - MAINTENANCE MATTERS -

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.

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