Ameron International Corp. adopted a shareholder rights agreement Tuesday designed to discourage abusive takeover tactics and encourage potential buyers to negotiate exclusively with the company.

The Pasadena-based industrial pipe infrastructure products maker said the agreement replaces a similar agreement which expired at the end of last year and was not adopted in response to a specific offer or takeover.

The rights, also called a “poison pill” strategy, would be triggered by a person acquiring or announcing an intention to acquire 20 percent or more of the company’s voting stock or if 50 percent or more of the total shares of the company were acquired or sold.

These plans are often an acknowledgement that the company may have become an acquisition candidate.

Shares in Ameron gained 4 percent Wednesday to $101.74 in afternoon trading on the New York Stock Exchange. Shares have gained 30 percent so far this year.