Hangers and Snubbers

Question 1

Describe the types of strain and movement experienced by Plant Piping systems

Answer 1

• weight of piping
• process fluid contained in piping
• system components
• pressure and temperature induced expansion and contraction
• movement caused by system flow changes and pressure surges

Question 2

Purpose of pipe hangers

Answer 2

• support piping systems
• prevent damage by compensating for strains and movements
• standards are governed MSS, ANSI, ASME

Question 3

Types of pipe hangers

Answer 3

Consideration for hanger construction:
-pipe size, piping config, location, structural points to attach to

Flexible Hangers: support piping systems to allow for vertical movement due to thermal expansion.

2 types: Constant and Variable Support (use spring)

Rigid Hangers- no vertical movement

2 types: Horizontal and Vertical

Snubbers: a special type of hanger that slows the movement of piping

Question 4

Explain basic operation of mechanical snubber

Answer 4

Use a ball screen shaft and spring mechanism or rod and bearing assemblyto provide a braking action limiting the axial movement to maximum safely restrained acceleration

Mechanical snubbers limit ACCELERATION of movement

Hydraulic snubbers limit VELOCITY of movement

Question 5

Explain basic operation of Hydraulic Snubbers

Answer 5

2 on each RCP and 2 on each SG, they are different types but operate the same

Below activation limit- hydraulic fluid is forced from one side of piston to the other via a control valve with an orifice cut into seat. Fluid reservoir maintains head on both sides of piston

Activation limit exceeded- motion in excess of lockup velocity closes the control valves creating hydraulic lock

Question 6

Identify major components of hydraulic snubber

Answer 6

SG is a 650 KIP snubber. Hydraulic fluid is Fyrquel

RCP is an 850 KIP snubber, has a spring loaded reservoir and uses GE SF-1154 for its fluid

Common components are tube(houses piston), nameplate, piston rod, rod head chevron packing, bleed and drain plugs, control valves and reservoir

KIP=1000 lbs of compressive or tensile force
Activation level=amount of acceleration that causes snubber to resist movement

Question 7

Normal inspection criteria for mechanical Snubbers

Answer 7

No visible damage.

After transient, normal visual inspection and can verify freedom of movement by removing one end pin and push or pull to verify free movement

Question 8

Normal inspection criteria for hydraulic Snubbers

Answer 8

• no visible leaks(plugs, fittings, valves, seals, reservoir, tubing)
• hanger fasteners can support Snubber function
• hydraulic oil level adequate- reservoir level in SH and reservoir piston position on RCP
• hanger support structure and foundation intact
• no indication of deformation, physical damage or excess movement
• fasteners are not loose or missing
• proper installation/orientation
• no obstruction to movement

Question 9

5 and 10 year STs

Answer 9

5 year- sample hydraulic fluid for water, viscosity and particulates. Replace fluid if necessary.

Control Room needs to be notified prior to sample due to potential alarm (RCP)

10 year- fluid sample, vendor functional test(bleedrate and lockup)

For RCP, replace chevron head packing, replace reservoir rod wiper

SG- replace chevron packing