There are a number of companies that provide heater pigging services. The key to having a good outcome is by having an experienced pigging contractor that has successfully pigged Coker heaters in the past. Additionally, have a pre-work discussion that clearly states the goals of the pigging and the expectation you have of the contractor. Having someone from your company oversee the progress of the pigging is helpful in providing guidance to the contractor during the pigging operation. Requiring a written summary of the decoking operation also assists in preparing for the future pigging operations.
The companies that have been successfully used in the USA and in Canada are; DDT, CEDA, Clean Harbors, CokeBusters. I think some of these companies operate outside of the US as well. Their websites are; http://www.decoking.com http://www.ceda.com http://www.cleanharbors.com http://www.cokebusters.com They all have some information discussing the technology.
Doing an intelligent pig after the decoke can tell you how much coke remains in the tubes. Quest and A.HAK are two inspection companies that do intelligent pigging. I believe CokeBusters will also do intelligent pigging after decoking the heater as well.
Alternately, some sites have used a borescope to confirm all the coke was removed from the heater by inspecting a few random tubes.