BOLTED JOINT ASSEMBLY WHY BOLTS COME LOOSE and WHAT TO DO ABOUT IT

1
BOLTED JOINT ASSEMBLYWHY BOLTS COME LOOSEand
WHAT TO DO ABOUT IT
WIND ENERGY FIELD SERVICE TECHNICIANS
2

• 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 persons use of, or reliance upon these
  generally accepted methods and principles.

3
PROPER BOLTING IS CRITICAL TO WIND TOWER
PRODUCTIVITY
WHY DO BOLTS COME LOOSE?
4
MOST COMMON CAUSES FOR LOOSENING

• INITIAL UNDER-TIGHTENING
• INITIAL OVERTIGHTENING
• REPEATED RE-TIGHTENING
• ELASTIC INTERACTION (UNEVEN TIGHTENING)
• EMBEDMENT
• VIBRATION AND SHEAR MOVEMENT

5
REMEMBER THE CONCEPT OF PRE-LOAD
1
SPRING BAR OR DIVING BOARD

• EXTERNAL LOADS DONT SEPARATE THE JOINT UNTIL
  THEY EXCEED PRE-LOAD
• THE GREATER THE PRE-LOAD (UP TO THE YIELD POINT
  OF THE BOLT) THE MORE STABLE THE JOINT

"PRE-LOAD"
INITIAL UNDER-TIGHTENING
6
TOO LITTLE PRE-LOAD MEANS THE JOINT CAN MOVE
10,000 LBS. PRE-LOAD -JOINT WONT MOVE UNTIL
EXTERNAL LOAD EXCEEDS 10,000 LBS.

• ZERO PRE-LOAD
• THE JOINT MOVES

• ONCE THE JOINT MOVES
• THE NUTS WILL LOOSEN
• LOAD WILL BE QUICKLY LOST IN THE JOINT
• UNPROTECTED BOLT SUBJECTED TO OUTSIDE SHOCKS MAY
  FAIL

INITIAL UNDER-TIGHTENING
7
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 DONT OFTEN COME LOOSE
• (EXAMPLE OF A 1-8 UN BOLT)

INITIAL UNDER-TIGHTENING
8

• UNCONTROLLED TIGHTENING CAN TAKE THE BOLTS BEYOND
  YIELD AND INTO THE PLASTIC RANGE

INITIAL OVER-TIGHTENING
9

• BOLTS IN THIS CONDITION CANNNOT BE RELIED ON TO
  MAINTAIN SUFFICIENT LOAD UNDER VARYING OPERATING
  CONDITIONS

INITIAL OVER-TIGHTENING
10

• LOOSE BOLTS ARE A SYMPTOM OF A PROBLEM, NOT THE
  CAUSE
• 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

AXIAL MISALIGNMENT
RADIAL MISALIGNMENT
REPEATED RE-TIGHTENING
11

• 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

EMBEDMENT
12

• 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)

ELASTIC INTERACTION (UNEVEN TIGHTENING)
13
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?
VIBRATION AND SHEAR MOVEMENT
14
VIBRATION AND SHEAR LOADING
Research as shown that its 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
VIBRATION AND SHEAR MOVEMENT
15
Junker Vibration Test Machines
Junker designed a machine that allows the
effectiveness of a fastener locking method to be
evaluated
Examples of Junker Test Machines
VIBRATION AND SHEAR MOVEMENT
16

• 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

VIBRATION AND SHEAR MOVEMENT
17
Lets Try A Few Questions To Ensure We Understand
About Wind Applications And Loosening
(Quiz 2)
18

• 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?

19

• 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?

20

• Quiz answers
• D. All of these
• Gradual incremental tightening and a check pass
  on all bolts
• False. Most of the bolts are close enough to one
  another to have great effect on each other.
• True
• B. Tighten the bolts properly in the first place
• True. Each manufacturer will have specific Bolt
  Torque Specifications and Work Instructions
  which must be followed)