One of the most common historical usage of asbestos containing products was thermal insulation on boilers, tanks and pipes to prevent heat loss. There was as many different manufacturers of these materials as there was asbestos insulation formulas. Companies began to provide labels for the finished product in order to distinguish there brand and type from the myriad of other manufacturers on the millions of miles of insulated pipe.

Pipe insulation was manufactured as a combination of asbestos fibers with other substances such as; alternating sheets of plain and corrugated asbestos paper cemented together; laminated layers of asbestos felt in which tiny spongy particles were embedded; or asbestos fiber mixed with basic carbonate of magnesia.

Earlier pipe insulation (or covering) consisted of the pipe being covered with flexible millboard then with a thick layer of hair-felt, while the entire insulation is covered with oiled canvas which at first was stitched together and then later was metal banded.

Pipe insulation was was available in the form of half sections, segmental blocks, blankets and tape. Half sections were held in place by metal bands or by loops of soft iron wire. For extra thick insulation, the hlaf sections were applied in two layers. Whole sections could be used only when the insulation was sufficiently flexible to allow the insulation to be slipped over the pipe when split lengthwise along one side.

Pipe Insulation By Type

Pipe insulation manufacturing process not only took advantage of the strength and heat resistance of the asbestos fibers but it increased the insulating capacity of the pipe insulation by adding air spaces in the corrugation of the asbestos paper or the small air spaces in the more plaster-like materials.

Magnesia pipe insulation is made from magnesia alba or magnesium carbonate which is an inroganic, inert product that was for many years used in medicine (milk of magnesia) and in other various manufacturing. In 1885 Hiram M Hanmore, a pipe coverer, began to mix magnesia with other pipe covering materials and actually patented his idea. In about the same time manufacturers of magnesia for medical purposes also began to discover the insulation capacity of the fine, white magnesia powder. Experiments soon were under way mixing magnesia with many materials in an effort to find the best insulator. Asbestos fibers was one of those materials and it acted as a binder to give strength and cohesion to the magnesia sludge which then could be cast or molded into standard shapes and dried. The optimium mix became 85 percent magnesia and 15 percent asbestos fibers. The principle type of asbestos fiber was chrysotile though amosite and crocidolite were also used. 85 percent magnesia pipe removed today after nearly a half a century or more is in just as perfect condition as when it was originally installed.

Airecell pipe insulation is made of alternating layers of plain and corrugated asbestos paper firmly bonded together to form a strong, heatproof insulation. The corrugation which are typically one quarter inch deep retain the non-conductive properties of the pipe insulation.

Wool felt sectional pipe insulation is composed of laminated wool felt with an inner lining of waterproof asbestos paper for insulation on cold service water pipes and to prevent sweat and retard freezing. This pipe insulation was also used on hot water lines. The pipe insulation was wrapped with a cotton jacket or white gloss paper or washable aluminum enamel jacket and secured with bands.

Multi-layer or paper-layer pipe insulation consists of many brown (cellulose) or dark greay (wool felt) layers with one or both layes of an outer light grey asbestos paper and an inner tar-impregnated black asbestos paper. This pipe insulation is covered with a cloth jacket to maintain its integrity.

Asbestos indented pipe insulation was specially manufactured for railway train services, locomotives and hoisting engines where there was an excess in vibration. The pipe insulation was made from asbestos paper that has been indented prior to rolling. It had high efficiency, strength, compactness and resistance to breakage and rough handling.

Nonpareil high pressure pipe insulation for steam lines was distinctive because it was the only pipe insulation made of diatomaceous earth and asbestos. Diatomaceous earth is composed of the skeletons or shells of microscopic life that grew in the ancient seas. Millions of diatoms fill a cubic square inch eacg made of silica and hollow filled with air giving it a remarkable heat insulating value. The mixture of diatomaceous earth and asbestos fibers could be bonded together in various shapes. The pipe insulation could withstand high temperatures without burning or disintegrating and therefore was well suited for superheated steam surfaces. This pipe insulation was excellent for the covering of underground steam lines because it could survive repeated wetting and drying.

Pipe Insulation By Manufacturer

Johns-Manville Corporation was founded in 1858 as the H. W. Johns Manufacturing Company of New York, N. Y. and was based on the pronciple uses of asbestos as fire resistant roofing material. In 1886 the imception of the Mnaville Covering Company of Milwaukee, Wisconsin was founded on the principle uses of asbestos as a heat insulating material. In 1901 H. W. Johns Manufacturing Company and Manville Pipe Covering Company merged to form H. W. Johns-Manville Company of New York, N. Y. The company was reincorporated as Johns-Manville Corporation in 1926.

Asbestocel pipe insulation was a Johns-Manville brand name for a cellular type aircell insulation for pipes carrying low pressure steam or hot water. The piep insulation was made of alternating layers of plain and corrugated, specially treated, moisture resistant, asbestos paper. The pipe insulation was covered with either white glaze, asbestos paper or regular canvas.

Asbesto-sponge pipe insulation was a Johns-Manville brand name for felted sectional pipe insulation made of fine flexible, tough fibers, interwoven in the form of cells and meshes for insulating pipe conveying steam at any pressure or temperatures up to 700 degrees F. This asbestos pipe covering could have had from 37 to 42 laminations per inch.

Keasbey and Mattison was founded by Henry G. Keasbey and Richard C. Mattison upon graduation from Phildaelphia College of Pharmacy in 1873. Keasbey and Mattison started by manufacturing of pharmaceutical preparations in Philadelphia and among their products was carbonate of magnesia. At this time steam power was developing rapidly and there was a demand for efficient insulation. In 1882 Hiram Hanmore was impressed with the extremely light weight of magnesium carbonate and applied like plaster to a steam boiler. Mr. Hnamore was purchasing significant quantities of magnesia from Keasbey and Mattison and this made Dr. Mattison curious as to its application. Upon contacting Mr. Hanmore, Dr. Mattison entered into an arrangement to sell insulating materialsand to manufacture molded pipe covering, block insulation and magnesium cement. Mr. Hanmore was using shredded hemp as the binder which deteriorated rapidly and it was Dr. Mattison idea to use heat resisting asbestos fibers for the reinforcement. Thus was born 85 percent magnesia insulation which became the standard for high-temperature thermal insulation for many years.

Keasbey and Mattison manufactured a combination pipe insulation that was suitable for temperatures up to 1900 degrees F. It consisted of an inner layer of calcined diatomaceous silica nad asbestos fiber mixed with abonding material. The diatomaceous silica is burned (calcined) at a temperature of approximately 2200 degrees F before being mixed with asbestos fibers in order to limit shrinkage of the finished product when in service. The outer wrap is 85 percent magnesia that has a low thermal conductivity but can not come in contact with temperatures above 600 dgrees F.

The Ehret Magnesia Manufacturing Company made Ehret pipe insulation 85 percent Magnesia by the trade name of Thermalite. Thermalite is a molded insulating material composed of basic magnesium carbonate reinforced with selected asbestos long fibers. It possessed high insulating qualities because of its inherent structure of thousands of minute, dead-air cells, formed by the interlocking magnesia chrystals. Another magnesia based pipe insulation manufactured by Ehret is Durocel. Durocel insulation is composed of specially heat-treated diatomaceous silicas, blended with carefully graded long asbestos fibers, magnesia carbonate and binders. Durocel is widely used for insulating high temperature pipelines. Other pipe insulation manufactured by Ehret are Ehret Asbestos Sponge Felt and Ehret Air Cell.