Corrosion inhibitor

The use of a compound as a corrosion inhibitor for metallic equipment, wherein the compound comprises a salt of an optionally substituted polycarboxylic acid or its anhydride, and/or the reaction product of the polycarboxylic acid or anhydride with an alcohol and/or amine, or the salt of the reaction product. A composition is defined comprising the compound and a further corrosion inhibitor additive. Also defines a method in which at least a portion of the metallic equipment is contacted by the compound, and the use of the compound and method whereby the salt is an alkali or amine. The optionally substituted polycarboxylic acid or anhydride may be a succinic acid or anhydride thereof. The substituent may be an alkyl or alkenyl group with 2-30 carbon atoms, or an alkaryl or aralkyl group. The amine salt may be tertiary, and the compound may comprise a di alkali metal salt or mono amine salt of a hydrocarbyl substituted dicarboxylic acid or anhydride thereof. The alcohol may comprise polyalkylene glycol, and the amine may be primary or secondary. The metallic equipment may be metallic oilfield equipment, pipelines, or temperature control jackets, and the surface may be in contact with corrosive or aqueous fluid.