Here are some pictures of asbestos-containing boiler and pipe insulation. Typically, a boiler is insulated with a “mud-like” material that is manually packed on a boiler surface to insulate it and keep it more efficient. This material was usually not sold “ready to use” and was required to be mixed on-site. Therefore the amount of asbestos that was actually mixed in to the mud-like material varies. This material was also used on pipe fittings (elbows, tees, etc.)
Pipe insulation was sold in preformed sections about three feet long. A very common application was a corrugated material that had asbestos material applied between the layers of cardboard. This material was called “Air-Cell”. In most cases, a cloth was wrapped around the insulation and light-weight metal bands were installed to secure the insulation to pipe. We sometimes see Air-Cell used as boiler insulation also.