into the structure. During construction, the reinforcing mats or fabrics 

 are overlapped or oriented to provide adequate distribution of stress and 

 .to give uniformity to the cross section of the structure. In the filament- 

 winding process, continuous strands of resin-impregnated glass are wound 

 onto a mandrel. Inner layers are commonly resin-rich. Large-capacity (up 

 to 280,000 gal.) storage tanks have been constructed by a form of multiple- 

 strand winding,^ and large-diameter piping (9 to 13 ft) has been manufac- 



cr Q 



tured for power plant cooling and sewage systems. Pope-"" describes the 

 manufacture of a 9-f t-diameter pipe for a conductor circulating water sys- 

 tem of a 325-MW electric power plant. The pipe was manufactured by using 

 a 65-degree filament helix angle overwind and a dual resin system consist- 

 ing of a 100-mil-thick inner layer of a flexible bend polyester resin and 

 an isophthalic resin for the structural wall to give a minimum wall thick- 

 ness of 1 1/8 in. The pipe was fabricated in 50-ft sections; 60 field 

 joints were required to assemble 2500 ft of pipe. Cheetham^^ lists some 

 of the advantages and limitations of the use of FRP in the marine environ- 

 ment . 



Some FRP advantages are : 



1. Corrosion free in seawater 



2. High strength-to-weight ratio 



3. Resistant to marine biological attack (borers, etc), but will foul. 

 Some FRP limitations are: 



1. Low elastic modulus; deflections could be unacceptably large and 

 elastic instability must be monitored. 



2. Does not flow plastically when its elastic limit is exceeded. 

 Failure occurs by resin fracture and disruption of the glass/resin bond. 

 Although FRP is capable of absorbing about four times as much strain energy 

 as steel in its elastic range, the capacity of steel to absorb an enormous 

 amount of extra energy by plastic deformation is absent in FRP. 



3. Absorbs and transmits water (but with resins suitable for marine 

 use, correctly postcured, the amount is insignificant). Water absorption 

 causes loss of strength by hydrolyzing the glass filament surfaces and by 

 disrupting the glass/resin bond. The correct surface finish applied to 

 the glass (chemical treatment which enables the resin to bond chemically to 



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