Standard snubbers

Introduction

Standard Snubbers (DAST) are used for all applications in conventional plants.
Snubbers are made with standard components, mainly available on stock.

Raw materials

Stainless steel rod with chemical nickel coating or chrominium
Body an internal parts in high quality carbon steel, surface protection by painting.

Dynamic characteristics at ambient temperature, 15°C to 35°C

Hereofter standard values, (others available on demand)
F_N is the Nominal load of the snubber

Locking speed:

2 mm/s to 10 mm/s or as requested

Drag force at slow speeds, before locking

f < 500N if F_N ≤ 30 kN
f < 2.0 % F_N if 30 kN < F_N ≤ 200 kN
f < 1.5 % F_N if F_N > 200 kN

Drift speed after locking,

at F_N : 0.1 mm/s to 2.0 mm/s or as requested

Peak-to-peak motion under sinus alternating load F_N from 3 to 10 Hz (depending on model)

< 4 mm if F_N ≤ 100 kN
< 5 mm if F_N ≤ 600 kN
< 6 mm up to F_N = 600 kN
< 8 mm for stroke more than 300 mm

Environment conditions

Temperature:

Normal operating conditions : 0°C to +80°C
Minimum storage temperature : – 30°C

Humidity: 100 %
External pressure:

Service pressure : 1 bar
Accidental pressure : 5 bar

Total dose of radiations: 600 kGy

Stiffness

Snubber stiffness is defined according to the following diagram where:

Peak-to-Peak is the total stroke under alternative load
And Snubber Stiffness is: K=(2 x F_N)/Peak-to-peak

* Tolerance on stiffness value : ± 25%

Permissible load in kN

The permissible load in terms of dynamic stress in the table below has been calculated in accordance with RCCM code vol. H level S1.

Load definition :

Normal/Disturbed – Level A/B: Here are estimated all loads due to normal functioning, including normal transitional regime during operation of the plant. And also some disturbed loads due to normal functioning of the plant.
Emergency : Level C: Here are estimated all loads outside to normal operation due to particulars situations, possibly safety shutdown earthquake.
Faulted : Level D: Here are estimated all loads due to accidental situations. The snubbers should undergo verification after such an event.

Stroke: Up to 300 mm

Stroke: From 300 mm to 450 mm

Life under dynamic stress

The snubbers may be subject to the total dynamic loads below, without any adverse effect on operating, at temperature less than 80°C.

Dimensions

Other load, stroke or characteristics on demand.