Corrosion inhibitors containing amphoteric surfactants

1 . A method for inhibiting corrosion on a metal surface, said method comprising contacting said metal surface with a composition comprising a metal salt of the compound of the formula (1)

in which R 1 is C 1 - to C 29 -alkyl, C 2 - to C 29 -alkenyl, C 6 - to C 30 -aryl or C 7 - to C 30 -akylaryl, and an amphoteric surfactant.

2 . The method of claim 1 , wherein R 1 is an alkyl or alkenyl group having 7 to 17 carbon atoms.

3 . The method of claim 1 , wherein the metal salt is an alkali metal salt.

4 . The method of claim 1 , wherein the amphoteric surfactant is selected from the group consisting of a compound of the formulae (2) to (14)

in which

R is C 4 - to C 22 -alkyl, C 4 - to C 22 -alkenyl or C 4 - to C 22 -alkylaryl

R1 is C 1 - to C 3 -alkyl, C 1 - to C 3 -hydroxyalkyl

R3 is methyl or -A-(OA) n -OH

R4 is -A-(OA) n -OH

A is a C 2 - to C 4 -alkylene group

m is a number from 1 to 4

n is a number from 1 to 4

x is a number from 0 to 10

M is H, an alkali metal, alkaline earth metal, ammonium or alkanolammonium.

5 . The method of claim 1 , wherein a total amount of metal salt to amphoteric surfactant is from 5 to 5000 ppm.

6 . The method of claim 1 , wherein a weight ratio of metal salt to amphoteric surfactant is from 1:9 to 9:1.

7 . The method of claim 1 , wherein said composition further comprises a hydrocarbon and said metal surface is an apparatus for conveying and transporting the hydrocarbon.

8 . The method of claim 1 , wherein the composition further comprises a metal processing composition.

9 . A composition containing at least one metal salt of a compound of the formula (1)

in which R 1 is C 1 - to C 29 -alkyl, C 2 - to C 29 -alkenyl, C 6 - to C 30 -aryl or C 7 - to C 30 -alkylaryl, and at least one amphoteric surfactant.

10 . The composition as claimed in claim 9 , wherein a weight ratio of metal salt to amphoteric surfactant is from 9:1 to 1:9.