hello raju,
               I do not consider myself an expert or a very good speller, but I have been repairing cast iron for over 12 years. When I was asking the same queston, I got so many different answers it was crazy. I've used many differant E-Ni-55 and found that when it comes to  welding 55 ni money is not an option.I've tried and tested everything from cheap to very exspensive brands and have found that exspensive is by far the way to go.
Cold welding is the best for me. For surface cracks I would grind crack down 3/4 the way thru, then take a torch and using a oxydizing flame burn off carbon build up in crack (when done properly you will see litttle particals of carbon sparkle off).
Using a 3/32" rod, weld a bead at a right angle across the start and stop of the crack. This will keep the crack from spreading (I've been told by engineers that drilling a hole at the ends of a crack is not a good practice).
Then run a bead along the ground out crack about 1 inch (no weaving) then you have to stress relieve the weld bead by penning the weld with a ballpin hammer real good. If it's hard to get to, I have used a needle scaler, but be sure the air does not exausts out the front of the scaler as it can cool weld too fast.Then repeat till your done keeping the cast iron cool to touch. Rod size can be 1/8"for bigger jobs. Length of weld bead should not be longer than rod diameter x 10. Then stop, deslag,  pean,  let cool then go again. I've been using this method for years and have had good luck with it.
As for as the WPS I was told there are none, but never looked into it any more.Sure hope this helps.
best of luck.
                 Lee D.