DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)

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Nov 25, 2013 (3 years and 23 days ago)

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DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)

DISCUSSION ON FABRICATION OF LARGE PANEL
STEEL BEAM FOR A BOILER (600MW)

ABSTRACT

With the
ever
-
increasing capacity of
domestic power plant's
single
instal
led
,
the design size and weight of
large
panel

steel
beam

are also
increasing. Due to
the difficult
ie
s
, such as
o
verlength

ultra
-
high

overweight of
i
t,

as well as

the overall manufacturing

transportation and
installation, so taking into account the economic and applicability to
the
design of
large p
anel steel beam,

we divided the whole beam into two
parts

upper beam and lower

beam. When they are delivered
to the
installation site,

we connect them
through the flange
, which connect the
contact surface of
two beams

with large numbers of
high
-
strength bolts.
This kind of beam is known as stoplog,

the

contact sur
face
i
n the middle
is called flange connection as shown
in Fig
.

1.

There are a great

difference between stoplog and
single

beam,
of
course the manufacture of stoplog is relatively difficult. stoplog

not only
need
a strict control of
each size and camber of upper and lower be
am,
but also
have to ensure the consistency of camber after
assembly;
to
ensure the close contact of
the upper and lower beam flange surface
,and
each bolt hole can be put on a bolt
; strictly control the welding
deformation
,

in particular
the angular defor
mation

warping deformation
and sidewise bending of the flange surface.
Therefore, how to control
camber

welding distortion

and
the rate of perforation of the group

for the
entire beam,

is the key to the production of
stoplog
.

KEYWORDS:

large panel steel beam; w
elding method;

welding
deformation control;

camber control
.







Fig.
1

DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


FOREWORD

Steel

structure for a boiler
consist
s

of column, beam
, vertical
support
,
lateral

support, support beam,
lifting
beam and large
panel steel

beam.
I
n
the
framework of
600MW units
,
the large panel steel beam is
in
stalled in
the top

of
framework

and its elevation
is

about 80 meters
, and
through the
connection of
small pa
nel steel beam
, support beam

and lifting beam,
form a long
-
span structures as a whole
. Al
l the equipment
s
,

which weight
is about 500t
,

are

hanging on the large panel steel beam
. There are three
aspects, which are t
he key
s

to the production of
the large panel steel beam,
welding
,
deformation control
, the lifting and turnover technology
,
so
all
the
production methods are carried out around these three points.

In 2005
,

Metal Structure Factory

(my work unit) took charge of the
p
roduction of
the steelwork project of
Yi
M
in Power Plant 600MW

of
Inner Mongolia

s
generating units, which was designed by
the Harbin
Boiler Plant
. T
he main technical parameters

are

in Table 1. The largest
plate beam
can be seen from the table
is
plate

"D
"

for the size
29100mm×1500mm
×5000mm, net weight 151.8t, materials for Q345B;
f
lange plate thickness of 120mm, web thickness

of 40mm; there are more
than 900 High
-
strength bolt hole
s

in the web and flange plate
.
B
ecause of
the high material requirements
,
size
,
thickness
,
weight,
so there are a lot
of difficulties, ne
i
ther in

cold
work
ing,
n
or
in
welding

or lift
ing.
According to

the practical experience, combined with the actual
condition
of
Yi
M
in

project
,
this article tries to
introduce the production technology
of large panel steel beam and explain the key links, based on
in
-
depth
exploration
s

of the thick plate welding,
deform
ation control, set aside
arch camber, the
scribing and
assembly, and other areas
.

Table
1

Item

Size

L
ongth


mm


Upper weight

(kg)

Lower weight

(kg)

Gross weight

(kg)

Panel beam“B”

H5000X1200X90X40

29100

68124

47739.4

116505

Panel beam“C”

H5000X1300X100X40

29100

73190.7

53153.6

126985.9

Panel beam“D”

H5000X1500X120X40

29100

85975.2

65106.4

151776.8

Panel beam“E”

H5000X1300X110X40

29100

76055.1

56000.6

132697.3

DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


1.

P
re
-
production

According to
structure features

of the
large panel
st
eel beam and

lifting
capacity,
the
plate
cutting
of flange and web plates

should be completed
in the workshop. I
n advance of
welding, the flange and web
plates
must

be carried out sand
-
blast
ing
(blasting level Sa2.5),
then

pre
-
paint
ing
primer (film thickness of not less than 25μm).
B
efore the start of
construction,
we need

to sweep away a
large
site for the production
,
lifting and turnover
of large plate girder

in order to ensure the normal
construction
.
After
produce the upper and l
ower beams separately
, we
prepare the
pre
-
assembl
ing.

2
.

Materials and layout requirements

2.
1
Steel material must be met
with

a corresponding contract and
physical

&

chemical indicators of
design. Before stocking
materials
, they must be
tested approach to
the

quality c
ertificate of steel products
to ensure the
pl
ate surface without any defects

and

preclude any
unqualified

raw
materials.

2
.2
Each plate which thickness is n
ot less than 60mm

should be carried out
by 100% ultrasonic testing, acceptance criteria
30.96.244 by

U
ltrasonic
T
esting

Procedure For S
teel
Pla
te
Of

P
ressure
V
essel

,

quality
level
of
steel
plate
for

.

Each plate should have
Additional marking,
and all the
flange and web plates of large panel steel beam must
be
take
n

the
transplanting of ide
ntification
,

in accordance with the relevant standards.

2.
3
We make the arrangement of the splicing joint in the light of the
drawings and technical requirements
. After checking the drawings, we
could cut the plates,

to make sure the weld joint
s

keep off th
e bearing
plate
s

and group of holes.

2.
4
I
f the
plate
s

for panel
steel
girder

need

to

splic
e, the splicing joints
must be taken ultrasonic testing
, the testing range is

30mm plus 2 times
the thickness of the plate
from both sides of welding line
.
D
o n
ot all
ow

any defects

to affect the quality
.

3
.

Flange and web processing

3.1
Flange plate

The
flange plates’ thickness of
beam

"D"
is

120mm,
due to the
rigid
ity
,
high technical requirements for welding

and
machining difficult
, so
DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


flange plate is

one of the diffic
ulties in production.


3.1.1
C
utti
ng plates

In order to eliminate micro
-
cracks in the materials
,

as well as the
possible

cracks
while
cutting,
we reserve 5mm
margin from both side o
f

the

width
,

and then dig out
the extras by using a
n

edge planer
.

At the
sam
e time,
pay attention not to
strik
e

arc

on the flange plate, to prevent
any
cracks and
any
crack source
s
.

3.1.2

G
roove processing an
d
assembly

The flange plates use
Automatic Submerge
-
arc Welding

when splicing

grooves
,

the type of the groove
is shown as
Fig
.

2.

While fitting up the
plates on the platform, we should control the
alignment tolerance

≤ 1mm,
Interface gap


0.5
mm
,
straightness

of
total length
≤ 3mm.

















Fig.
2

3.1.3

Welding and heat treatment

If the thickness of the flange is

greater than or equal to 38mm,
then the
whole beam should be taken
heat treatment. Normally,
prehea
t
temperature

must be
more than 100

. However,
in the light of the
difference in
material microstructure and yield strength
,

for some
DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


materials the preheat temperature should be

above
150

,
preheat
temperature

is an

important measure
to ensure the
weldin
g

quality
.
After
p
reheat temperature reached

the

requirement,
us
e

grinding wheel
to grind
the
welding

beads
,
then weld the weld joints layer by layer according to
the welding procedure.
The weld root of n
egative
side should be cleared,
then use grinding wh
eel to grind out the
carburiz
ed

layer
. After welding
one side, turn over the plate and weld the other side, to ensure the layer
temperature and
reduce the welding deformation.

3.2
Web plate

Large
panel steel girder "D", for example,

the
upper
web size
29100
mm × 3054mm,
and the
lower
web

size 29100mm × 1654mm,
is
welded by many
steel plate
s

(shown in Fig
.
3).
Unreasonable
order of
splicing
,
ill
-
adjusted planeness and unreasonable
welding technology, will
bring a lot of stress in the

welding joint,
leading to a

large
deformation,
causing
a great impact o
n

the

structure performance. Therefore,

we
should pay particular attention to the cutting process of the web plate,

as
follow
:








Fig.
3

Fig.
4

3.2.1
F
or single plate, we must

control the dimension strictly, especially in
the process of plate
-
cutting and grooving.

3.2.2
As show
n in Figure 4, according to
welding

order
,
we
assemble

and
weld the

weld

joint


,

,

respective
ly
.

A
lignment tolerance

≤ 1mm,
Interface gap ≤
0.5
mm
;

U
sin
g
automatic
submerge
-
arc welding,
guarantee
ing the adjusting
-
plane,

because this
working procedure

is very
important to the
flatness

of the entire web.

3.2.3
Welding
the long weld joint


as shown
in Fig
.
4.
B
ecause the
grooves of each side

are all pre
-
machi
ned
, and the
precision

of
assembly

DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


impact the welding quality directly,
so the precision must be controlled
seriously. While welding the weld joint, although the difficulty in
turnover is huge, but we must weld
by turns

according to procedure, at
first the

face side, then reverse.

3.
3
Determine the camber

Stoplog will

create

downwarp under the action of dead load,
in order to
compensate the
deformation
, we
have to

make a certain degree of upwarp
when we
manufacture

it
.
T
he largest arch for

s
tandards

is
10 ~
30mm.

Upwarping
is crucial
to the
manufacture

of stoplog, how to control the
camber consistency
of the upper and lower beams
i
s very important and
difficult.
S
o in the actual production process, we can acquire r
egulated

arch by using
diverse

methods, the
s
tability

of the upwarp is closely
related to the
p
roduction

m
ethods
. So the production procedure should be
fully analyzed the
characteristics of production methods.

3.3.1
Main methods of
Camber control


A
cquire arch by
us
ing

welding
shrinkage stress
.
G
enerally, we can
increase the weld joints of the lower beam, to increase the shrinkage
stress by adjusting the welding orders of flanges and webs of upper and
lower beams.


A
cquire arch by
us
ing

flame strai
ghtening
.
H
eat the back of the
bottom flange along the web,

or heat some
triangular

hot zones, where
located at the
stiffiener
s of the lower web, at the same time, heat the
corresponding parts of the
bottom
flange.

T
his method takes advantage of
heating me
tal at the
constraint condition

and cooling, so that the beam can
require camber

by arising from
shrinkage stress
.


A
cquire arch by
making precast web
.

A
fter setting the camber

in the
web, then cut the camber curves on the upper and lower web. Finally,
assemble and weld the precast web with the top and bottom flanges.

The
former

two methods
are widely applied in the pr
oduction of small
camber beam, however, with the fading away of the internal stress,
upwarp will still disappear, so we have to adopt some kinds of
reinforcement program to restore the arch.

At the same time, due to the
poor uniformity caused by heating, a
nd related to the size and the number
of hot zone, so we found that it was very hard to control the flame
DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


straightening. Therefore, the former two processes are not desirable,
after
summarizing the characteristics and the past experiences in the
production

of stoplog, we often use precast web to require arch.

3.3.2
Acquire arch by making precast web

P
recast beam is
manufacture
d

by mak
ing

a arch web which cut by gas
cutt
ing according to the arch curve.
A
lthough precast arch relate to
t
echnology
m
aking
, but th
e
stability

and

uniformity

will be
influence
d by
some factors
.


D
etermine the largest technology arch.
I
f there are many weld joints
of stiffieners on the beam, then the
shrinkage stress of upper beam exceed
the lower beam, this
will

lead to a
decrease

on arch.

Besides

in the light
of deadweight, so
the actual arch va
lue is usually greater than
design
value
.

The determining of the arch value relates to the span and
rigidity

of
the beam.


T
here are two ways to produce precast arch on the web
, but
according to the
characteristics

of stoplog, we precast arch when cutting
the web plates.
T
he key is to
develop the amount of camber.
B
ecause of
the deformation after welding
H
-
shaped steel
, the pre
-
camber maybe
change, and the changes in upper and lower beam are different.

4
.

Assembly
of H
-
shaped steel and
welding of stiffiener
s

4.1
Assembly of H
-
shaped steel

A
ssembly two H
-
shaped steels of the stoplog respectively,
then

weld
the main weld joints.
P
ut the web plate on the jig frame, and measure the
levelness by a water level.
Two flange plates placed on the both side of
web, and
these three plates must be tightened together, no gap between
web and flanges is permitted.
D
raw the center line along the vertical of
flange plate,

bu
r
nish and clean up the rust and oil stains within 40mm of
both side
s
, find the center line of flange plat
e and closing line of web and
flange,
then spot weld the support board. H
-
shaped steel should be firmly
spot welded,

spot

welding length

of 120~150mm,
weld

spacing between
200 ~ 300mm,

weld leg as 10mm.

Before spot welding the weld surface
should be prehea
ted,
preheat temperature

between 100~150

.
S
pot
welding while assembly, and use a
straight steel ruler

to measure if the
web stands in the center of flanges, and keep adjusting. Using a
DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


horizontal

assemblage

to treat the
L
arge H
-
shaped steel, first install

the
top flange, then the bottom flange, take
welding deformation

in to
consideration when the web needs cut
ting

the grooves.

4.2
Welding order of the main fillets

4.2.1
First weld fillet

of thick plates
,
then weld the fillet of flange face.

Therefore,
the u
pper
beam should be welded
the fillet of top

flange
,
then
the bottom flange;
a
nd the lower
beam should

be welded the fillet of
bottom flange first,

then the top flange.
T
he flanges could be assembled
into a certain angle,

then
backing weld

starts from the
larger angle side, if
after backing weld the angle still can

t content the
requirement
,

there is
one thing can be done, that is to weld the larger angle side of the main
weld joint first.
A
fter the
assemblage

of H
-
shaped steel, lift the
weld
holder
, but fi
nd a suitable lifting lug

wh
ile

lift
ting
, both the weight of the
two f
rame crane
s

and
plastic deformation

of the H
-
shaped steel should be
taken into consideration while the steels are under lifting.
L
ay down the
steel w
hen the weld holder was lift
ed

to be
the boat
-
shaped
, put two
iron
wedge
s on the flange to fix it.

4.2.2
T
he main weld joints should be welded at the boat
-
shaped

position.
A
s a result of the large size weld leg, we often use multi
-
layer welding in
order to prevent
larger

deformation
.
E
ach fill
et should use a welding
machine, and each weld joint should be welded
once, four main fillets
should be welded in the same direction in order to decrease welding
deformation, especially to control the
warping deformation
.
W
elding
starts from one side of fl
ange, and starts from the middle to the two sides
together by using multi
-
layer, until the weld leg meet with the
requirement, then turn

over
the beam and weld it.

4
.3
Assembly and welding of stiffieners

There are many
stiffieners and
connecting plate
s on
the stoplog,

the
welding quality
and technology have a direct impact
on the
assembly
and
camber
of
a

beam
.
A
fter adjusting the beam, scribe on the plate and then
assemble stiffieners
.
T
he flange face and the support plate should be
tightened, to prevent welding deformation of the flange face.

4.3.1
T
he length and width of the support plate need to be planed down,
and the joint face of support plate and flanges should be milled, try to
DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


tig
hten the spaces between the joint face and
flanges, no spaces are
permitted,

so as to minimize the
welding shrinkage

of the support plates,
and avoid any
influence

of camber.

4.3.2
T
he blanking size of the supporting plates and connecting plates
based on th
e size of
real size of the beam.
A
fter welding the whole beam,
if there
is still a certain deformation

on the web that can

t be corrected,
then change the size of the support plates and connecting plates according
to the practical situation in order to kee
p the web flat.

4.3.3
T
he hole location benchmark of the connecting plate: because of the
upwarping of stoplog 25mm, so the
gusset plate
s should be moved up,

the
holes which link the connecting plates and sub
-
beam should be drilled
based on the top flange;
the holes which link the upper and lower beams
should be drilled based on the flange face.

5
.

Control precision of flange face

5.1
Drill the flange face

Before assemblage,

the upper and lower flange
s

should be stacked
together,
and the flange face
s should b
e drilled on a
numerical control
machine. By using this method can reduce the workload, improve the
drilling rate, increase the high precision, but the best advantage is that the
two flange faces can be consistent to ensure that support and enhance the
rat
e of perforation.

5.2
Impact and measure on reshaping the flange face

Because the flange face will bring angular deformation when the main
weld joints were welded, through previous measurement of the flange
plate of similar H
-
shaped steel, the post
-
welding
deformation can reach
the largest size of 13mm.
I
f we don’t control or reshape, then the two
flange face
s

will have a lot of space, can’t achieve the quality
requirements.

One simple reshaping method is to carry out the flames on
the flange faces, but this

method will bring a great impact on the camber
of the entire beam, in general shouldn’t be used lightly.
We consider the
following
project

to deal with the flange surface on trial.

Use a 3000kN jack,
m
ak
e

a

reshaping
frame
, then reshape the flange
faces o
n it.

Advantage


Won’t cause camber deformation of the beam.

DISCUSSION ON FABRICATION OF LARGE PANEL STEEL BEAM FOR A BOILER (600MW)


Disadvantage

Divide the entire beam into many parts, then use a jack
to reshape them, low speed.

In the study we found that, in order to overcome the slow speed, we
can produce several reshaping frames
, and reshape the beam at
multi
-
point. The verticality of flange face and web can be corrected at the
same time. Flange surface uses hydraulic jacks, verticality of web uses
flame straightening.

SUMMARY

In the production process of the boiler steel structu
re,

by means of
c
onstantly sum
ming
-
up

and
improve
ment
,
we
ris
e
to create a better
performance.
From the production in practice of several projects of the
panel steel beam of
600MW generating units, we come to experience:
for
the production of
panel steel b
eam
, first
,
the entire project
should be well
related
to
materials; Second,
weld preheating and the
welding process
are
considered to b
e the most important factors to

the welding quality
; Third,
stress relief treatment
should
n

t be underestimated; Fourth,
set
ting

aside
arch camber is
the guarantee
to meet the requirements; Fifth,
every
relevant size
s

should under control
.

Through considering a comprehensive analysis of all the factors, we
can
simply
complete
the lifting and flipping of
the entire
beam by us
ing
shaped grid assembly and welding equipment. Only if we adopt
reasonable welding methods and

control measures,
we can

be able to
reduce and eliminate the welding residual stress and residual deformation
,
and control the camber, warping and sidewise bend
ing of the
stoplog
, and
so on
.

Then we are fully capable of ensuring the quality for the stoplog of
large
-
scale steel structure of the
600MW power plant.



MengJ
ie (Sophia)

China Petroleum Offshore Engineering Company

CNPC International English Training Class (2)

2008.12.23