ISO-14692 addresses the analysis of Fiber Reinforced Plastic (FRP) pipe. Qualification is based on the comparison of actual stresses, hoop and axial, to a failure envelope. See BS 7159 for the CAESAR II approach for FRP pipe analysis.
ISO-14692 2017
ISO-14692 2017 distinguishes between the reinforced wall thickness and the total wall thickness. The reinforced wall thickness does not include the liner (inside) and sheath (outside) the reinforced wall. In CAESAR II, define the reinforced dimension (not including the liner and sheath) for Diameter and Wt/Sch, and separately define Refract Thk, Refract Density, Liner Thk, and Liner Density.
ISO 14692 2017 defines four axial code stresses and a single hoop code stress, and has a single allowable failure envelope. The vertical axis defines the axial stress and the horizontal axis defines the hoop stress.
The software picks the stress nearest to its envelope boundary based on differences instead of the stress-to-allowable ratio. Because the ISO 14692 2017 allowable envelope defines negative values for the axial allowable stress, reports now display positive and negative stress, allowable stress, and ratio/percent values for the stress envelope.
When the axial stress is a positive number that is close to the negative allowable boundary, the stress-to-allowable ratio is negative. It is also possible for the negative ratio to become greater than 1.0 by magnitude. For example, if the stress is 1457 psi and the allowable is –1236 psi, then the ratio is –1.18. Because the failure envelope has negative boundaries, this is a passing value because the stress point is inside the envelope.
A negative ratio always means passing criteria.
Stresses (Multiple Code/Allow) Report for ISO-14692 2017
CAESAR II picks a single "worst" axial stress from the four code stresses and displays this value in the Stresses (Multiple Code/Allow) Report.
If all four axial stresses are inside the failure envelope, then the software subtracts the axial stresses from their respective envelope allowable. The smallest difference determines the worst axial stress and allowable. The software compares each axial stress to both the tensile and compressive boundaries of the failure envelope.
If one or more axial stresses are outside the envelope, then the software subtracts the axial stresses from their respective envelope allowable. The largest difference determines the worst axial stress and allowable. If only one axial stress is outside the envelope, then this is the worst axial stress.
The hoop stress and the allowable hl(2:1) also display in the report.
Stresses Report for ISO-14692 2017
The governing code stress displays in the Stresses Report.
If the worst axial stress and hoop stress are both inside the failure envelope, then the software determines which stress is nearest to its envelope boundary based on differences. The software uses the stress nearest to its boundary as the code stress.
If the axial stress is outside the envelope and the hoop stress is inside, then the software uses the axial stress as the code stress.
If the hoop stress is outside the envelope, then the software uses the hoop stress as the code stress.
CAESAR II Determines
The software selects a stress equation based on the calculated axial load in the piping system. The software applies the fully restrained stress calculation when the axial pipe lo ad is within 2.5% of the limiting load or otherwise applies the unrestrained stress calculations. The limiting load is the load to fully constrain the pipe axially against the linear superposition of thermal expansion and pressure elongation (when the Bourdon pressure effect is selected in the Configuration Editor or in Special Execution Parameters). The restrained/unrestrained status can change from element to element.
The Bourdon effect (Trans only) is always considered for FRP pipe, regardless of the Activate Bourdon Effects setting used.
The software uses the following equations:
Bourdon Force: [Sp – (nah * Sh)] * AREA
where:
Sp = P * Ri2/(Ro,m2 – Ri2)
Sh = P * Ri / Tm
AREA = p * (Ro,m2 – Ri2)
nah = Minor Poisson ratio
P = Pressure
All geometric quantities are reinforced. The subscript m means percentage variation.