DUAL TECH - System Composition

Dual Tech is a composite, or dual laminate, piping system consisting of either a polypropylene or PVDF liner that is strengthened with a fiber glass reinforced thermoset resin system.

Advantages over steel lined piping

  • No exterior maintenance required
  • Lighter in weight
  • Can be field fabricated
  • Liner bonded to exterior
  • Full vacuum rated
  • No condensate drains are required
  • Heat fusion joints - longer piping runs without flanges

Thermoplastics, particularly Polypropylene (PP) and Polyvinylidiene Fluoride (PVDF), have excellent chemical resistance to most process chemicals and wastes. However, they suffer a significant loss of physical properties (tensile strength, beam strength, etc.) when subjected to elevated temperature applications. FRP systems possess physical properties, which far exceed thermoplastics but are decidedly inferior to thermoplastic’s chemical resistance.

The objective of the Dual Tech System is to achieve a reliable and effective combination of these dissimilar plastic materials that enhances the performance of each component while minimizing the individual weaknesses. By successfully bonding the FRP Laminate onto the thermoplastic liner Simtech has created a piping product with capabilities which far exceed the potential of either piping component.

DUAL TECH PP- Reinforced Polypropylene piping: 1"-12"*

DUAL TECH VF- Reinforced Polyvinylidiene Fluoride piping: 1"-12"*

*Larger sizes available on request.

DUAL TECH PIPE LINERS

POLYVINYLIDIENE FLUORIDE (PVDF)

The PVDF liner used in Dual Tech is extruded (seamless) from natural un-pigmented 100% pure Polyvinylidiene Fluoride polymer. There are no additives or fillers, which could be leached from the liner to contaminate the media. After extrusion the liner is annealed to relieve inherent stresses caused by the extrusion process.

Chemical Compatibility – PVDF possesses outstanding resistance to most inorganic chemical, acids, salts, aromatic and aliphatic hydrocarbons, halogens, organic acids and alcohols.

PVDF is suitable for certain polar solvents, hot concentrated alkalis, fuming sulfuric, amines or pyridine.

Temperature Range – PVDF can be subjected to continuous operating temperatures as high as 280 F.

Permeability – PVDF has one of the lowest permeation coefficients of all the fluorocarbon resins. It is particularly superior to PTFE and FEP.

POLYPROPYLENE (PP)

The PP liner used in Dual Tech is 150 PSI rated through 2" diameter and 90 PSI rated 2-"-12" diameter. The liner is seamless, extruded and stress relieved. Produced from Isotatic Homopolymer the material has temperature stabilizers added to provide enhanced resistance to aggressive media at elevated temperatures.

Chemical Compatibility – Polypropylene is particularly suited for handling dilute acids, some strong acids, alkali and organic solvents. PP should not be used for halogens, halogenated hydrocarbons, and aromatics or highly concentrated oxidizing acids.

Temperature Range – Polypropylene can be subjected to continuous operating temperatures as high as 210 F.

Permeability – When compared to PVC and other more amorphous thermoplastics, polypropylene possesses a relatively high gas permeation coefficient. It is important to incorporate thick liners in PP lined composite systems. Any increase in the thickness produces a reduction in permeability disproportionately greater than the increase in thickness.

PIPE REINFORCEMENT

Dual Tech pipe is produced by filament winding glass fiber and resin in multiple layers over the liner pipe at the precise winding angles necessary to produce the pressure capabilities desired. Filament winding is especially desirable in order to obtain very high hoop stress values, and to outstanding beam strength and stiffness this process provides.

RESIN SYSTEM

The standard resin system employed in manufacture of Dual Tech is Dow Chemical Company’s Derakane 470 Vinylester Resin with UV inhibitors. Derakane 470 provides broader chemical compatibility than other vinylesters and a continuous operating temperature range of 250 F.

LAMINATE INTERFACE

The surface of the liners are prepared in proprietary processes which provide significant lap shear strength between the liner and the FRP laminate. This is essential to maximizing system service life.

LINER BEHAVIOR

The effects of temperature change play an important role in the life expectancy of the liner in any lined pipe system. This is particularly true in lined steel systems where the liner cannot be effectively bonded or laminated to the steel jacket. As the temperature in the system increases, the liner material wants to expand but cannot because it is totally enclosed by the steel jacket.

Consequently the material goes into compression. When the temperature returns to ambient the compressive stress reverts to tensile stress. Each succeeding thermal cycle will result in slightly less compressive stress when the pipe returns to operating temperature and slightly more tensile stress when the pipe returns to ambient. Eventually the material will see only tensile stress due to shrinkage induced by thermal cycling. When the liner reaches this condition all the stresses will be concentrated in the area where the liner has been heated and flared to form the flange face.

In Dual Laminate FRP Pipe Systems the liner will behave in the same manner as with lined steel except that it is possible to create a bond between the liner and the FRP overwrap. (Caution is advised with Dual Laminate pipe because many fabricators do not or cannot create a satisfactory bond between the liner and the structural FRP overwrap.) If a satisfactory bond is achieved the liner will be restrained in a manner which prevents dimensional change until the liner eventually delaminates. Annealing the liner greatly increases the time required for delamination to occur. If delamination should occur, the use of molded fitting liners becomes critical to the continued system integrity.

SYSTEM PRESSURE RATING

Both Dual Tech PP and Dual Tech VF Systems will require flanges for joining to pumps, tanks valves or other equipment. Only ANSI 150 lb. flanges are available with Dual Tech. Consequently Dual Tech is limited to 150-PSI service at the corresponding maximum allowable operating temperature.

Cautions

WATER HAMMER

Shock waves or pressure surges commonly referred to as water hammer are caused by rapid or abrupt change in fluid velocity within the pipe system. In some cases the surges can attain a magnitude sufficient to damage the system. The amount of surge experienced is dependent upon the modulus of the pipe material, the density and velocity of the fluid, the line length and the speed at which flow is stopped or started.

Dual Tech pipe is capable of withstanding surges many times its rated pressure, however, it is recommended that the density and velocity of the fluid, the line length and the speed at which flow is stopped or started.  These problems are of course not unique to Dual Tech piping.

Avoid

  • Valves that close or open instantly
  • Starting pumps into empty discharge lines unless a slow opening valve is used to gradually increase flow
  • Slow closing check valves
  • It may also be advisable to employ feedback loops or surge suppressors to eliminate water hammer.

  Dual Tech Design Guidelines