An i-beam is a vertical support in an inflatable floor applying restrictive force to two hemispheres of fabric. These i-beams give the self-bailing floor the "ribbed" look providing the floor it's mattress like function. Typically, i-beam floors have a nominal operating pressure of ~1.75 - 2.75 psi. The pressure is regulated by the pressure relief valve (PRV) installed in the floor. On occasion, these i-beams fail and you're left with an over sized bubble in the floor that is noticeably different than the rest of the i-beams.
If a raft has an i-beam floor construction, it also has a v-tape installed to seal the two hemispheres of fabric together around the edges. V-tape is a piece of material folded into a "V" and adhered to each hemisphere to create the air-holding floor. The self bailing holes or grommet holes are then punched an 1"+ outside the v-tape. The v-tape is blown if air is "leaking out the drain holes" of your raft.
Baffles are what separate each chamber from the next. They are built to be a flexible diaphragm. Most rafts are constructed with two or more baffles. You will know when you have blown a baffle if while inflating one chamber, you notice a chamber next to it start to inflate as well.
Seams are where each paneled section of raft material is overlap and attached to each other.
Causes of failure for i-beams, v-tape, baffles & seams
The common causes of failure for i-beams, v-tape, baffles and seams are all related. See below for detail an explanations of the main reasons why these parts would fail.
Over pressurization - The floor or chamber has been inflated beyond the pressure rated for the raft.
I-beam and v-tape floors - there should always an appropriate pressure relief valve (PRV) installed. There are a variety of PRVs ranging from 1.75 PSI (pounds per square inch) up to 4.5 PSI. This PRV will release air once the PSI has been reached. These PRVs commonly get clogged with silt and do not work as they are intended. The PRV can be working properly, but with a quick change in pressure the PRV can't always keep up with releasing the pressure fast enough (transition from the water to the boat ramp).
Baffles and seams - over inflating one chamber before inflating the other chambers
Trapped Moisture - Moisture in the floor or chamber attacks the adhesive bond and/or mildew destroys the stitching.
Manufacturer Defect - Rarely the raft manufacturer has not adhered the i-beam, v-tape, baffle or seam properly.