During pigging the tubes will jump. It depends on tube i.d., buildup of coke, and u-bend vs plug headers as to how much.
1. smaller i.d. means higher pressures to run the pig
2. more buildup means the pig can hangup, needs a blast of pressure to get it moving again
3. plug headers hang pigs up constantly, start/stop/start/stop. with u-bends it is much easier to keep consistent speed (lower pressures, minimal jumping)
If the pigging company has pigged the heater before ask them about tubes jumping, pigs hanging up (they should be able to look at the old pig run sheets and estimate). You may have to wait untill the pass is opened up (a couple hours) before working inside the heater. Any great movement with a u-bend heater is during the first couple hours.
If the heater has different tube sizes there is potential for the pig entering the smaller i.d. tube, it needs a blast to get it out.
Any time the pig stops inside the heater the tubes will jump when it starts moving again, this ranges from barely noticeable with your hand on the launcher to tubes jumping a foot up in the air. It wont really change between companies or operators, it depends on the coke buildup and heater design. (actually the operator will have some control but not a lot)
You may have an idea if tube wall thickness is an issue, I have pigged a couple hundred heaters, seen many broken tube hangers, falling brick, launchers jumping off blocking etc but have only seen 1 tube failure (heard of 3 or 4?).
Jumping tubes is your main problem.
MAKE SURE the pigging company knows there are people inside, if the pig gets stuck higher pressures will be used to get it out (no matter what we tell you) and workers should get out first.
sorry I cant sign this but I can be honest if anonomous
I hope this helps