AED

AED


Explosive decompression also known as Rapid gas decompression is a structural failure in the form of blistering, internal cracking that occurs due to gas permeation into the sealing material.

SEAL EXTRUSION

Seal extrusion occurs when a gas or liquid at high pressure forces the seal material into the clearance gap between the  mating surfaces.

The greater the diametric clearance and the higher the differential pressure, the more likely extrusion will occur. Weakening of the polymer due to elevated temperature and/or chemical attack or swelling also influences potential for seal  extrusion.

• The rubber seals contains pores and rigid inclusion during the production,fluids and gases in contact with elastomer surfaces are absorbed into the material.
• The absorbed gas diffuses into the elastomer until fully occupied.
• During high pressure the gas which is absorbed will be in the compressed state.
• When the external pressure is suddenly reduced the compressed gas expands into the rubber material in which the pores inflate leads to tensile strain or stress.
• If the stress or strain is higher than the strength of the elastomer the cracks initiate and propagate.

Pressure:

The gas decompression damage generally increase with pressure.

The threshold pressure above which damage may occur depends on gas combination and hardness of the rubber. The Pressure range is of 2500 psi and 500 psi range.

Hardness:

Increasing the hardness of elastomeric seal normally increase its rapid gas decompression resistance.

The average hardness if 17.5 bar is 50 IRHD and 90 IRHD is 34.5 bar.

Crack and Fracture of the material:

Crack are caused by rapid gas decompression are initiated internally mostly and few times externally.

Internal cracks can be caused by excessive thermal expansion, liquid swell or due to high stress at low temperature.

High temperature:

The gas permeation properties of elastomers  strongly depend on temperature.
The high temperature range of the material is 150 -200 degree celsius, some as high as 300 degree Celsius.

Low temperature:

AED seals materials must be capable of withstanding the very low temperature like -40 degree celsius, after installation the stretch in seals below 0 degree celsius must not exceed 5% of ID , because high stretch may cause failure when the seal become brittle at low temperature.

Some of the  elastomeric products used in the Oil and gas industry are

Elastomeric oil field components
Gaskets	Drill pipe protectors
	Down hole packers
o-rings	Drill bit seals
	Inflatable packers
Hoses	Annular blowout preventers
	Valve seals
Cables	Ram blowout preventors
	Drilling hoses
Cable jackets	Drill motor seals
	Pressure accumulator
Pump stators	Swab caps
	Wellhead seals

The elastomers are exposure to various chemicals in the oil field industry, the chemical exposure oilfield service are

1. Crude oil
2. natural gas( Methane)
3. Amine corrosive inhibitors
4. Hydrogen sulfide
5. Salt water (brine)
6.Carbon di oxide
7.Solvents such as methanol
8. Hydraulic fluid
9.Diesel oil
10.Inorganic and organic acids
11.Coolants

Commercial elastomers in AED

For Oil and gas industry the types of elastomers used are NBR, HNBR, FKM, FFKM. Based on the specification the elastomers are chosen.In general the common material used is FKM.


The various testing Standards  for testing the elastomers in the oil and gas industries are.

1. Durometer Hardness- ASTM D- 2240
2.Tear Strength -ASTM  D-624
3.Compression Set- ASTM D 395
4.Low temperature brittle point- ASTM D -2137

High pressure and chemical aging testing:

Many oilfield application require certification to special standards like NORSOK or NACE, NORSOK stands for Norsk Sokkels Konkuranseposisjon which is a set of standard developed by the Norwegian Petroleum industry.
NACE standard are set by international corrosion society.

Chemical aging- NORSOK M710
Rapid gas decompression  RGD - NACE  TMO 192-2003