Effective key length of Two-Key Triple-DES
Des is 56 bits/key   with 2Des   the key is is 56*2 or 112bits.  It is not multiplicative like 56 * 55 

3des is EDE  encrypt with k1, decrypt with k2 and encrypt with k3.  or 3*56 or 168 bits.  Quit often, cypherblock chaining is used with the sicond or third pass.  The cbc makes it even or difficult to guess the encryption keys.Decryption = DED