毕业论文

打赏
当前位置: 毕业论文 > 外文文献翻译 >

大型高压泵列车英文文献和翻译(2)

时间:2018-04-13 15:54来源:毕业论文
The same holds true for the middle segment, 4,000-5,500, but at a slower rate. It is the opposite, however, in the large segment, beyond 5,500. The trend is for axially split machines, Reliability, av


The  same  holds  true  for  the  middle  segment,
4,000-5,500,  but at a  slower rate.
It  is  the  opposite,  however,  in  the  large
segment,  beyond  5,500.  The  trend  is  for  axially
split  machines,  Reliability,  availability  and
efficiency  are  the  most  important  factors  on
these  large  installations,  generally  under  BOO/
BOT  financing  schemes. Equipment  first  cost  is
secondary.
As for energy recovery, today's plants  feature
turbines  of  the  Pelton  type.  Initially,  reverse
running  pumps  and,  in  some  cases,  Francis
turbines  were  used.  However,  as  they  became
more  reliable,  the  more  efficient  Pelton  turbine
became the element of choice. The Pelton  turbine
allows a more simple plant design and simplifies
the operation.
Other energy recovery devices are being con-
sidered but,  to  date,  some  are  restricted  to  small
plants or retrofits and others need to gather expe-
rience and operating hours on  larger units.
3. Materials of construction. Alloy 885
Metallurgy  is  one  factor  that  makes  special
the  specification  and  construction  of a  seawater
reverse osmosis high-pressure pump.
Typical seawater where reverse osmosis plants
are  installed  has  salt  contents  ranging  from
20,000  to  40,000 ppm  and  temperatures  from  15
to  35°C.  Dissolved  oxygen  levels  are moderate.
Fluid velocities within the pump  are  rather high;
values  of 40m/s  are  representative.  Fortunately,
inorganic suspended solids  levels are very low.
Simplistic  material  recommendations  are,
therefore,  impractical  and  the  designer  has  to
consider, among other things,  localized corrosion
(pitting  and  crevice  corrosion)  and  stress
corrosion  cracking (SCC).  Castability  and weld-
ability are also to be taken  into account.
The  families of materials  under consideration
are:  300  series  austenitic  stainless  steels,  duplex
stainless  steels,  super  austenitic  stainless  steels
and specialized alloys.
3.1.  300 series austenitic stainless steels
Their  susceptibility  to  localized  corrosion
(pitting  and  crevice)  and  SCC  make  them  a
marginal  material  for  this  service.  Improved
service  life  has  been  experienced  with  steels
containing molybdenum  in  colder  seawater.  The
chrome oxide  layer  is very  tenacious  and,  there- fore,  the  corrosion  rate  is not velocity sensitive.
They  are  readily  available  and  easily  weld
repaired (the low carbon grades) in the field.
3.2. Duplex stainless  steels
Materials with  a  ferrite  and  austenitic micro-
structure, hence the name "duplex"; ferrite is the
matrix  phase.  Higher  levels  of chrome, molyb-
denum and nitrogen make them more resistant to 大型高压泵列车英文文献和翻译(2):http://www.youerw.com/fanyi/lunwen_13158.html
------分隔线----------------------------
推荐内容