STRESS CORROSION

When certain materials are subjected to the combined effects of sustained tensile stress and corrosive environment, over a period of time, structural failure may occur at a stress lower than the material would normally withstand. This phenomenon is known as stress corrosion cracking, and it may occur in an environment which is not severely corrosive in the normal sense. To avoid failure, tensile stresses must not exceed a threshold value which is a function of the material and the application.

The boss in which a Lee Plug is installed will generally not be susceptible to stress corrosion cracking if a highly resistant boss material is used, and the D/d ratio is 2.5 or greater. The Lee Plug is not subject to stress corrosion since it is in compression throughout. Other values of D/d may be required if the mechanical properties of the boss differ significantly from those of the plug.

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ALLOY CONDITION YIELD
STRESS
(MIN.)
%
ELONG.
(MIN.)
2024 Alum T851 58 ksi 5
6061 Alum (a) T6 35 ksi 10
7075 Alum T73 56 ksi 8
355, 356 Cast Alum T6 17 ksi 3
15-5PH Cres (b) 1075 125 ksi 13
300 Series Cres (a) Cold Drawn 75 ksi typ. 35 typ.
4130 Cast Steel Quenched &
Tempered
85 ksi 16
6AI-4V Titanium (a) Annealed 120 ksi 10
Monel Alloys (a) Cold Drawn 85 ksi typ. 20 typ.
Inconel Alloy 600 Annealed 35 ksi 30

(a) All conditions are highly resistant to SCC.

(b) Condition H1000 and above is highly resistant to SCC.

*The following alloys have low resistance to SCC, and are generally not recommended for Lee plug bosses (partial list):
Alum: 2024-T3 & T4, 7075-T6, Cres: 440c (all cond.)

 

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