The chapter represents Dickens' use of several different types of irony.
-Dramatic Irony: At this point in the novel, the reader knows that Pip has helped an escaped convict in the nearby vicinity, but no one else but Pip, the convict, and the reader is privy to this information. So, when the soldiers knock on the Gargerys' door asking for a blacksmith and begin discussing the escape of convicts, the reader knows why Pip is extremely worried about getting in trouble.
-Situational Irony: Pip's convict wants nothing more than to escape what he feels is an unjust sentence, and he almost does so. But when he finds that his arch enemy, "the young man," has also escaped, he transfers all his effort to capturing and trying to murder the other convict. He wastes precious time in the meantime. It is as if he does not even realize that he hates the other convict for getting him imprisoned in the first place, and yet he allows his vengeance to prevent him from escaping his hated lot in life.
Also, when Pip's convict realizes that Pip has not turned him in to the authorities, he lies to protect Pip. He goes from threatening Pip's life in the book's opening to protecting him from his sister's wrath in Chapter 5.