Reliability Rebecca Seviour

ESS  Cross  Func,onal  Work  Group:  Reliability  

Problem  Statement  •  The  ESS  has  defined  achieving  95%  reliability  as  a  key  goal  for  the  facility.      

•  What  is  meant  by  95%  reliability  for  the  ESS  has  to  be  defined  in  qualita@ve  terms  to  form  a  set  of  user  centric  defini@ons,  which  are  inline  with  defini@ons  used  by  the  interna@onal  accelerator  community  

•  Although  many  accelerator  facili@es  place  great  importance  on  reliability  of  opera@on  liEle  has  been  done  to  integrate  reliability  analysis  into  the  accelerator  design  process.  To  achieve  the  levels  of  reliability  required  for  the  ESS  adop@ng  “design  for  reliability”  (FEMA,  DFR,  etc.)  into  the  ESS  design  process  will  be  necessary  

•  Exis@ng  accelerator  neutron  source  facili@es  currently  achieve  availability  less  than  90%,  For  the  ESS  to  achieve  a  reliability  of  95%  we  need  to  clearly  iden@fy  key  limi@ng  factors  and  develop  mi@ga@on  strategies  that  cover  the  whole  accelerator  life  @me  from  the  design  process,  to  opera@on  and  the  maintenance  planning  of  the  facility.  

•  To  understand  reliability  in  the  context  of  the  ESS  requires  knowledge  of  the  impact  of  each  system  and  sub-­‐system  across  all  divisions  of  the  ESS  requiring  integra@on  between  divisions,  and  greater  understanding  of  the  role  each  group  contributes  to  the  design  process.  

Milestones    •  Qualita@ve  defini@ons  of  reliability  for  the  ESS,  in  line  with  those  used  by  the  accelerator  community  –  25th  April  2012  

•  Determine  the  acceptable  varia@on  in  beam  parameters  required  to  meet  the  reliability  defini@ons  –  15th  May  2012  

•  Iden@fy  of  key  high  risk  systems  and  possible  mi@ga@on  strategies  in  the  proposed  ESS  design    -­‐  August  2012  

•  Numerical  model  overview  of  impact  on  beam  of  instability/varia@on/failure  of  key  accelerator  systems.  –  July  2012  

•  Review  conven@onal  “Design  For  Reliability”  processes  and  examine  how  they  may  adopted  into  the  ESS  design  process  –  Sept  2012  

Deliverables    •  Technical  note  defining  reliability  for  the  ESS  –  May  2012  

•  Report  on  the  ESS  reliability,  iden@fying  probability  of  failure  of  key  systems  and  mi@ga@on  strategies  –  Sept  2012  

•  Report  on  routes  for  integra@on  of  Design  For  Reliability  prac@ces  into  an  itera@ve  ESS  design  procedure  –  August  2012  

Instruments  Division:  Reliability  defini,on  95%            1-­‐  The  average  delivered  flux  is  our  measure  of  reliability,  i.e.  95%  reliability  means  for  us  that  95%  of  planned  neutron  flux  is  delivered  for  the  instruments.      2-­‐  However,  the  way  that  95%  of  the  flux  is  delivered  maEers  a  lot  to  the  instruments  as  well.  That  means  we  define  the  desired  quality  of  the  reliability  addi@onally  to  the  quan@ty  of  flux  defined  by  the  reliability  criterion  (95%)  on  different  @me  scales.      3-­‐  We  here  define  this  quality  for  single  @me  scales  in  every  case  to  95%.        4-­‐  In  case  we  have  to  live  with  a  mixture  of  failure  to  deliver  on  the  different  @mescales,  the  defini@ons  have  to  be  adapted  so  that  the  total  of  flux  delivered  stays  with  95%,  indeed.        5-­‐  The  order  in  which  we  present  our  criteria  defines  priori@es,  i.e.  if  we  have  to  choose  only  the  first  (A)  defini@on  applies.      6-­‐  Quality  (@me  scale)  Criteria:      A.  Deliver  95%  neutron  flux  within  every  20  pulses        B.  Deliver  19  out  of  every  20  hours  in  total  95%  nominal  flux      C.  Deliver  95  out  of  100  days  in  total  95%  nominal  flux,  where  the  100  days  are  defined  in  advance.        7-­‐  Finally,  we  understand  that  the  95%  reliability  criterion  does  not  include  any  informa@on  on  the  @me  stability  of  the  pulse  delivery  (frequency)  yet.  We  therefore  ask  for  informa@on  on  that  issue  to  accelerator/target  as  that  might  possibly  have  an  impact  on  reliability  as  we  define  it  (Pulses  delivered  not  on  @me  must  be  counted  not  delivered  eventually).  

Reliability  is:  •   estimating,  •   controlling,  •   managing,  the  probability  of  failures  in  complex  systems.    

 

(...)  the  role  of  mathema8cal  and  sta8s8cal  methods  in  reliability  engineering  is  limited,  and  apprecia8on  of  the  uncertainty  is  important  in  order  to  minimize  the  chances  of  performing  inappropriate  analysis  and  of  genera8ng  misleading  results.      

(…)  prac%cal  engineering  must  take  precedence  in  determining  the  causes  of  problems  and  their  solu8ons        [PDT  O’Connor]  

-­‐   Availability  :    Fraction  time  system  meets  its  specification.    

-­‐   Reliability  :    probability  system  performs  intended  function  for  a  specified  time  interval  

-­‐   Mean  Time  Between  Failure  (MTBF):    mean  time  system  performs  to  spec,  during  a  given  time  interval.    -­‐   Mean  Down  Time  (MDT):    Mean  time  system  is  unavailable  due  to  a  failure.  Repair  time  plus  all  delays  associated  with  the  repair  (finding  the  spare  part,  etc).    -­‐  Mean  Time  To  Repair  (MTTR):  sum  of  corrective  maintenance  time  divided  by  the  total  number  of  failures  during  a  given  time  interval.  May  include  waiting  for  radiation  decay.  

Instruments  Division:  Reliability  defini,on  95%  (dra_  for  final  discussion)          1-­‐  The  average  delivered  flux  is  our  measure  of  reliability,  i.e.  95%  reliability  means  for  us  that  95%  of  planned  neutron  flux  is  delivered  for  the  instruments.      2-­‐  However,  the  way  that  95%  of  the  flux  is  delivered  maEers  a  lot  to  the  instruments  as  well.  That  means  we  define  the  desired  quality  of  the  reliability  addi@onally  to  the  quan@ty  of  flux  defined  by  the  reliability  criterion  (95%)  on  different  @me  scales.      3-­‐  We  here  define  this  quality  for  single  @me  scales  in  every  case  to  95%.        4-­‐  In  case  we  have  to  live  with  a  mixture  of  failure  to  deliver  on  the  different  @mescales,  the  defini@ons  have  to  be  adapted  so  that  the  total  of  flux  delivered  stays  with  95%,  indeed.        5-­‐  The  order  in  which  we  present  our  criteria  defines  priori@es,  i.e.  if  we  have  to  choose  only  the  first  (A)  defini@on  applies.      6-­‐  Quality  (@me  scale)  Criteria:      A.  Deliver  95%  neutron  flux  within  every  20  pulses        B.  Deliver  19  out  of  every  20  hours  in  total  95%  nominal  flux      C.  Deliver  95  out  of  100  days  in  total  95%  nominal  flux,  where  the  100  days  are  defined  in  advance.        7-­‐  Finally,  we  understand  that  the  95%  reliability  criterion  does  not  include  any  informa@on  on  the  @me  stability  of  the  pulse  delivery  (frequency)  yet.  We  therefore  ask  for  informa@on  on  that  issue  to  accelerator/target  as  that  might  possibly  have  an  impact  on  reliability  as  we  define  it  (Pulses  delivered  not  on  @me  must  be  counted  not  delivered  eventually).  

•  Within  the  framework  presented  this  defini@on  defines  the  availability  of  the  ESS  as  95%  •  In  terms  of  Neutron  pulse  need  to  discuss  what  and  how  this  is  defined      

•  Within  the  framework  presented  to  achieve  95%  availability  need  key  informa@on  to  proceed    

•  Define  acceptable  Neutron  pulse    

•  Availability,  reliability,  MTTR,  MTTF  required  for  Target  

•  For  target  to  produce  acceptable  Neutron  pulse  what  is  requirement  on  accelerator  

•  This  impacts  on  all  systems;  Control,  instruments,  services,  target,  accelerator  

•   Should  focus  on  user  centric  defini@ons  

 

�  Top-­‐Down  /  Deductive  �  Need  detailed  info  about  components  and  connections  �  Need  “solid”  database  of  components  �  Most  common:  Reliability  Block  Diagram  (RBD)  

�  Layout  of  RBD  usually  depends  on  system  state!  �  Fault  Tree  Analysis  (FTA)  

�  Determine  all  component  faults  that  lead  to  given  system  fault  �  Methods  for  availability  allocation  and  maintenability  

�  Integrated  Logistic  Support  (ILS)  �  Logistic  Support  Analysis  (LSA)  

�  Bottom-­‐Up  /  Inductive  �  Failure  Mode  and  Effects  (Criticality)  Analysis  (FMEA/FMECA)  

�  Can  be  performed  with  expert  judgment  on  relative  criticality  of  components  

�  Can  be  performed  also  with  less  detail  in  design  

Predic,ve  Methodologies  

•     Identification  of  possible  failure  modes  of  each  component  

•     Listing  of  all  the  envisaged  faults    

•     Analysis  of  the  effects  of  the  component  fault  on  the  performance  of  system  

•     Identification  of  preventive  and  corrective  actions  

•     Severity  ranking  of  the  faults  

•     Relative  frequency  of  faults  

Failure  Mode  and  Effects  Analysis  (FMEA)  

The  purpose  of  the  FMEA  is  to  take  actions  to  eliminate  or  reduce  failures,  starting  with  the  highest-­‐priority  ones.      Failures  are  prioritized  according  to  how  serious  their  consequences  are,  how  frequently  they  occur  and  how  easily  they  can  be  detected.    

Component  data  has  only  a  limited  role  on  system  reliability,  nature  of  connec@on  is  important!  

FMEA  in  the  design  process  

•  Two  key  areas  – Sub-­‐system  opera@onal  realiability  – Technological  performance    

•  Two  key  areas  – Sub-­‐system  opera@onal  realiability  – Technological  performance  

Failure  Frequency  and  Down@me  of  Electromagnets  Magnet  failures  (1997  to  2001),    SLAC  CATER  system.  Down@me  of  Accelerator  Due  to  Power  Supply  Failure  

•  Two  key  areas  – Sub-­‐system  opera@onal  realiability  – Technological  performance    

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MO103 Proceedings of LINAC08, Victoria, BC, Canada

Proton and Ion Accelerators and Applications

12

2E - Superconducting Linacs

SNS  experience  with  ellip@cal  cavi@es  

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