Transcript Principles of Bolting

BOLTED JOINT ASSEMBLY
WIND ENERGY FIELD SERVICE TECHNICIANS
WHY BOLTS COME LOOSE
and
WHAT TO DO ABOUT IT
HYTORC -WIND APPLICATIONS
©HYTORC 2009
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The following material is intended to make you aware of the commonly
accepted and recognized principles and methods used in assembling
bolted joints. However, every possible application of these methods
cannot be foreseen and these general guidelines do not supersede
any other applicable rules or regulations.
ALWAYS FOLLOW CURRENT COMPANY AND LOCAL SAFETY RULES
AND PROCEDURES WHEN PERFORMING ANY OF THE WORK
DESCRIBED IN THIS PRESENTATION.
The authors and sponsors of this course have no control over, and
assume no responsibility for any damage, injury or work interruptions
due to any person’s use of, or reliance upon these generally accepted
methods and principles.
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©HYTORC 2009
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PROPER BOLTING IS CRITICAL TO WIND TOWER
PRODUCTIVITY…
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©HYTORC 2009
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MOST COMMON CAUSES FOR LOOSENING:
 INITIAL UNDER-TIGHTENING
 INITIAL OVERTIGHTENING
 REPEATED RE-TIGHTENING
 ELASTIC INTERACTION (UNEVEN
TIGHTENING)
 EMBEDMENT
 VIBRATION AND SHEAR MOVEMENT
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©HYTORC 2009
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REMEMBER THE CONCEPT OF “PRE-LOAD”
SPRING BAR OR
“DIVING BOARD”
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10
10
10
10
10
10
10
10
10
10
BOARD PULLS
100 UP
 EXTERNAL LOADS DON’T SEPARATE
THE JOINT UNTIL THEY EXCEED
PRE-LOAD
 THE GREATER THE PRE-LOAD (UP
100
ROPE PULLS
100 DOWN
TO THE YIELD POINT OF THE BOLT)
THE MORE STABLE THE JOINT
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-WIND APPLICATIONS
INITIAL UNDER-TIGHTENING
©HYTORC 2009
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TOO LITTLE PRE-LOAD MEANS THE JOINT CAN
MOVE
10,000 LBS. PRE-LOAD ZERO PRE-LOAD –
THE JOINT MOVES
JOINT WON’T MOVE
UNTIL EXTERNAL LOAD
EXCEEDS 10,000 LBS.
ONCE THE JOINT MOVES:
 THE NUTS WILL LOOSEN
 LOAD WILL BE QUICKLY
LOST IN THE JOINT
 UNPROTECTED BOLT
SUBJECTED TO OUTSIDE
SHOCKS MAY FAIL
HYTORC
-WIND APPLICATIONS
INITIAL UNDER-TIGHTENING
©HYTORC 2009
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HOW DO WE SOLVE THE UNDERTIGHTENING
PROBLEM?
 ENSURE ADEQUATE PRE-LOAD ON THE BOLT
– KNOW YOUR SPECIFIED TARGET TORQUE OR LOAD
– MATCH TARGET TORQUE WITH LUBRICATION USED
– CHECK TORQUE, TENSION OR ELONGATION
– CRITICAL APPLICATIONS MEASURE AND AUDIT
– CALIBRATE YOUR EQUIPMENT REGULARLY
 TIGHT BOLTS JUST DON’T OFTEN COME LOOSE
– (EXAMPLE OF A 1-8 UN BOLT)
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-WIND APPLICATIONS
INITIAL UNDER-TIGHTENING
©HYTORC 2009
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PSI
S
T
R
E
S
S
T
E
N
S
I
O
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STRESS/STRAIN CURVE
.
ULTIMATE TENSILE STR.
.
YIELD
PLASTIC RANGE
ELASTIC RANGE
ΔL
STRAIN (STRETCH)
 UNCONTROLLED TIGHTENING CAN
TAKE THE BOLTS BEYOND YIELD AND
INTO THE “PLASTIC” RANGE
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APPLICATIONS
INITIAL -WIND
OVER-TIGHTENING
©HYTORC 2009
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 BOLTS IN THIS
CONDITION CANNNOT
BE RELIED ON TO
MAINTAIN SUFFICIENT
LOAD UNDER VARYING
OPERATING
CONDITIONS
*1
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APPLICATIONS
INITIAL -WIND
OVER-TIGHTENING
©HYTORC 2009
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 LOOSE BOLTS ARE A “SYMPTOM” OF A
PROBLEM, NOT THE CAUSE
AXIAL MISALIGNMENT
RADIAL MISALIGNMENT
 THE BOLTED JOINT IS A “SYSTEM” WHERE
MISALIGNMENT CAN CAUSE PROBLEMS
THAT BOLTS CANNOT SOLVE
 BOLTS ARE NOT JOINT ALIGNMENT TOOLS!
 REPEATED HAMMERING ON A LOOSE BOLT
JUST MAKES THE PROBLEM WORSE
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-WIND
APPLICATIONS
REPEATED
RE-TIGHTENING
©HYTORC 2009
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 EMBEDMENT = SMOOTHING &
SETTLING OF MATING SURFACES
UNDER LOAD AND ABRASION
 PAINT OR DIRT UNDER NUTS
 NON-PARALLEL SURFACES
 RE-TIGHTENING CAN AFFECT THE
TORQUE / LOAD RATIO
 FLANGES CAN AND DO DEFORM
OVER TIME
HYTORC EMBEDMENT
-WIND APPLICATIONS
©HYTORC 2009
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 MOST BOLTS ARE INTERDEPENDENT
(WHAT YOU DO TO ONE AFFECTS THE OTHERS)
 PARTICULARLY EVIDENT WITH
TENSIONING (A/B PRESSURES)
 REASON FOR GRADUAL STEPS AND
CROSS-PATTERN TIGHTENING
(SEE PATTERN EXAMPLES)
 MULTIPLE TOOLS (SIMULTORC)
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-WIND APPLICATIONS
ELASTIC
(UNEVEN TIGHTENING)
©HYTORC 2009
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Use of Locking Devices on Bolted Joints
Bolt locking devices have
been used for over a
hundred years but most
so-called lock nuts are
ineffective– why?
HYTORC
APPLICATIONS
VIBRATION-WIND
AND SHEAR
MOVEMENT
©HYTORC 2009
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VIBRATION AND SHEAR LOADING
Research as shown that it’s repeated shear loading (surfaces
sliding past one another) , not axial loading that causes bolts
to vibrate loose.
•Tight bolts clamp the plates
& friction keeps them from
sliding past one another
•No sliding, no loosening!
•Many joints use guide pins,
keyways or press-fit bolts to
resist shear movement
Machine bolts often have fine threads to help
resist loosening from this kind of vibration
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APPLICATIONS
VIBRATION-WIND
AND SHEAR
MOVEMENT
©HYTORC 2009
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Junker Vibration Test Machines
Examples of Junker Test Machines
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APPLICATIONS
VIBRATION-WIND
AND SHEAR
MOVEMENT
Junker designed a machine
that allows the effectiveness
of a fastener locking method
to be evaluated
©HYTORC 2009
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Junker and other researchers
have shown that some commonly
used locking methods are
ineffective.
Helical spring washers:
•Ineffective against vibration
•Crush and separate under the
pressure of industrial joints
HYTORC
APPLICATIONS
VIBRATION-WIND
AND SHEAR
MOVEMENT
©HYTORC 2009
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Let’s Try A Few Questions To Ensure
We Understand About Wind Applications And Loosening
(Quiz #2)
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©HYTORC 2009
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QUIZ
1. Proper bolting techniques are important during which phases of
wind turbine work?
A. Production
B. Installation
C. Maintenance
D. All of these
2. Elastic interaction refers to the loosening of one bolt when
others around it are tightened. How should this problem be
addressed? ________________________________________
3. T / F There is no need to worry about tightening bolts in
gradually increasing steps in wind turbines because what is
done to one bolt has very little effect on the others?
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QUIZ
4. T / F Shear loads try to move the two sides of a joint past one
another, while axial loads try to separate and compress the
joint?
5. It is rapidly vibrating shear loads that are most responsible for
bolts coming loose. Wind turbines have many joints that are
susceptible to this kind of vibration. The best thing I can do to
avoid bolts coming loose is:
A. Use loc-tite
B. Tighten properly in the first place
C. Use lock washers D. Avoid lubrication
6. T / F Each manufacturer has a specification document that tells
me the appropriate torque values and bolting procedures for
each critical joint in the tower and turbine?
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©HYTORC 2009
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Quiz answers:
1. D. All of these
2. Gradual incremental tightening and a check pass on all bolts
3. False. Most of the bolts are close enough to one another to have great
effect on each other.
4. True
5. B. Tighten the bolts properly in the first place
6. True. Each manufacturer will have specific Bolt Torque Specifications
and Work Instructions which must be followed)
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©HYTORC 2009
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