HANGERS AND SNUBBERS

Question 1

TERMINAL OBJECTIVE:
1 Under all operating plant conditions, describe the various types, the principles of
operation, and the failure mechanisms and symptoms of hangers and snubbers in
accordance with Station Documents and Procedures.

Answer 1

ANSWER ALL CARDS

Question 2

1.1 Describe the Types of Strain and Movement Experienced by Plant Piping Systems

Answer 2

• Weight of the piping
• Process fluid contained in the piping
• System components
• Pressure and temperature induced expansion and contraction
• Movement caused by system flow changes or pressure surges

Question 3

1.2 State the Purpose of Hangers

Answer 3

Pipe hangers are used to:
* Support piping systems.
* Prevent damage by compensating for strains and movements

Question 4

1.3 Describe the Different Types of Hangers

Answer 4

Flexible Hangers
* Constant Support Hangers
* Provide support throughout the full range of expansion and contraction
* Variable Support Hangers
* Support piping systems to allow for vertical movement due to thermal expansion

Rigid Hangers
* No vertical movement
* Two types – Horizontal AND Vertical Pipe Attachments

Snubbers Hydraulic and mechanical

Question 5

1.4 Explain the Basic Operation of Mechanical Snubbers

Answer 5

For the most part, snubbers are used as seismic restraints where loading is cyclic and requires
rapid alternating restraint in two directions along a single axis. Restraints for valve blowoff or water
hammer are typical applications.
Mechanical snubbers perform their duty through a couple different designs:
* Ball Screw Shaft and Spring Mechanism
* Verge and Rack Assembly.

Question 6

1.5 Explain the Basic Operation of Hydraulic Snubbers

Answer 6

Below The Activation Level

Hydraulic fluid is forced from one side of the snubber piston to the other side via a control valve
with an orifice cut into the seating surface. The orifice allows a path for a bleed and a continuous
minimum rate of motion after the restraining load is reached.
The fluid reservoir maintains a
positive head on both the
tension and the compression side
of the piston.

When Activation Level Exceeded

Initial motion is taken up by any clearance in the
pins and bearings. Motion in excess of lockup velocity closes the poppet valve
creating a hydraulic lock. Flow through the bleed
orifice is negligible.

Question 7

1.6 Describe Failure Modes and Symptoms of Hangers and Snubbers

Answer 7

Hydraulic Snubbers
Under normal operating conditions hydraulic snubbers are maintenance free. In severe service
(usually involving excessive vibration or high temperatures) the seals may become damaged.

Mechanical Snubbers
Failures can be caused by improper assembly, overheating of internal components caused by
welding (during fabrication), and sensitivity of the design to dirt, corrosion, and inadequate or
excessive lubrication.