In almost every single poker article I've read, they say never limp pre-flop.
Is there any situation where is justifiable to limp pre-flop? If yes, when should I limp?
As a general rule, it is most ideal to limp with a hand that has good odds compared to the investment. This is where pot odds and implied odds come into play. This way you can know when it is getting too expensive for you to continue pre-flop versus the odds of getting a winning hand.
On a more loose/aggressive table I personally restrict myself to limping pre-flop with a hand that I would call a raise pre-flop with if it comes to it. This way I am not giving away money to the over aggressive players. This depends very much on position.
justifiable to limp pre-flop? If yes, when should I limp?
The answer is yes, when your pot odds versus your investment makes sense. But it is very important to consider your position, image and the behaviour of the players in the hand, their positions and how they have acted in those positions in the past etc.
This Article provides a clear explanation of Pot Odds and touches on Implied Odds.
This Article is my favourite Implied Odds reference that I use.
I highly recommend at least touching on Reverse Implied Odds which will actually improve your pre-flop game and likely tighten your range (resulting in you getting out kicked less often, for example).
There are some scenarios where limping is fine. Some live tables can play very oddly, where a limp from you can induce a series of limps behind and then a big raise if you want a big pot built pre flop.
Also in heads up or 3 handed play people can be very aggressive pre flop and limping can frequently induce a raise.
Need to differentiate between open limp and limp. Open limp would be first to enter the pot and that is not standard play. Typically you would enter with a raise. You are not only getting money in the pot but you have fold equity and you get information. If you open limp with AA to slow play the problem is if the board comes up 667 you have done nothing to get players off that range. Most sources advised to open for the same raise - you might vary based on position and table but don't vary by hand.
Now limp call. Say you have blinds / table that does not raise pre flop, will call post flop, and have trouble noticing a straight or flush. I would call 89, 78, 67, 56 suited from mid or late. Pretty much only if you are playing fish. A table of play money that does not raise pre flop. And if you are on that table and get a real hand punish with a pot size raise.
Even on a good table with a couple in the pot and stacks behind on the button and not too expensive I would call mid suited connector or a mid pair. They are the type of hands you need to hit but could get a big payoff. You are not looking to push players off the pot.
If you are in early position, you should limp with two "pretty good" cards that are not "top" cards for raising. These include two face cards (jack and higher) that aren't paired. You should raise with face card pairs, and also AK, suited or not.
If you are in late position, it depends what's happened in front of you.
If only one or two "early position" players are in, you need early position cards (described in the first paragraph) to compete. If "a lot" (four or five) people have called, you can limp with "promising" hands such as small pairs and "suited connectors," 5-4 or higher. If everyone else has folded, and you have a "top one quarter" hand, you should raise to force out one or both blinds, not limp.