To provide an anti-rust agent which suppresses occurrence of rust even on an iron base material of a steel pipe thereby materializing a discoloration-free iron base material, the iron base material being exposed by working the steel pipe after pipe making, and to provide cleaning liquid including the anti-rust agent, and a cleaning method using the cleaning liquid.SOLUTION: In a first embodiment, an anti-rust agent for preventing occurrence of rust in water washing of a worked steel pipe is provided that includes ethylene diamine tetraacetate and oxycarboxylate. In a second embodiment, anti-rust cleaning liquid is provided that includes the anti-rust agent in the first embodiment and water. In a third embodiment, an anti-rust agent is provided that is identical to the anti-rust agent in the first embodiment except that the anti-rust agent includes 1-10 mass% of ethylene diamine tetraacetate and 5-30 mass% of oxycarboxylate, and contains 5-50 pts.mass of the ethylene diamine tetraacetate based on 100 pts.wt. of the oxycarboxylate. In a fourth embodiment, anti-rust cleaning liquid is provided that is identical to the anti-rust cleaning liquid in the second embodiment except that the anti-rust cleaning liquid has a pH of 6-11 and an anti-rust agent concentration of 0.2-2%.SELECTED DRAWING: None
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