Hello everyone!

I would like to open here about ISO 14692 qualified stress.

The ISO 14692 states that the sum of all axial stresss σa shall not exceed values defined by the factored long term envelope, that is,

σa,sum < (1-r)(σh,sum/2) + (f2)(A1)(A2)(A3)(r/2)(σqs)---eq.1

How to get the value of qualified stress σqs?

The Caesar II states that the qualified stress is same as the long term hoop stress,

σqs = σhl(2:1).

σhl(2:1) = 2 σal(2:1) ----eq.2
σal(2:1) = σhl(2:1)/2 ---eq.3

While the ASME B31.3 states that the HDBS shal be obtained by the procedure in ASTM D2992. HDBS shall be multiplied by a service factor of 0.5 to get the hydrostatic design stress or HDS.
HDS = HDBS * 0.5 -----eq.4

The equation 3 and eq. 4 looks like the same, so the HDS is equal to σal(2:1) and σhl(2:1) is equals to HBDS.

So I conclude that the qualified stress σqs is the same as HDBS. Please correct me if Im wrong with my interpretation, this is a very serious matter.

Thank you and regards,

Clyde

HDS(B31.3)=HDS(ASTM F 412)
=
“The estimated maximum tensile stress the material is capable of withstanding continuously with a high degree of certainty that failure of the pipe will not occur. This stress is circumferential when internal hydrostatic water pressure is applied”
= 0.5 (B31.3) *
[
HDBS(B31.3)=HDB(ASTM D2992)=
“A hoop stress developed for fiberglass pipe by this practice and multiplied by a service design factor to obtain an HDS”
=
Table 1 valve against the given LTHP(ASTM D2992) calculated value
]

σqs(ISO 14692)
=
Pq(ISO 14692)*D/2t (D=mean reinf. dia, t=reinf. Thk.)
Pq(ISO 14692]=f1(ISO14692)*
[
LTHP(ASTM D2992)
=
“The estimated internal pressure of the piping product that, when applied cyclically, will cause failure of the product after a specified number of cycles by Procedure A or a specified number of hours by Procedure B”
]

So your comparisons as well as conclusions are not valid.
May I ask why you are mixing B31.3 and ISO 14692.
You should ask vendor for for Pq or σq and be aware what you are getting from the vendor, since the values are quoted for a particular service life. ISO default is 20 years

Concentrate on getting Lower Confidence Limit value from the vendor.

Satheesh

So how about the Qualified Stress in ISO 14692,we only have the information HBD in the material properties of FRP pipe. While ISO 14692 defines Qs=PD/2t only. What necessary information that is needed for Qs value from the vendor?

Clyde,

The given HDB is equal to σqs of ISO under the following conditions.

1- HDB is calculated as per Annex A of D2992 following procedure B (or procedure A if applicable i.e in case cyclic loading)
2- The given HDB is the actual calculated value and not the categorized nominal value obtained from table 1/2 of D2992
3- The given HDB is 97.5% lower confidence limit and is not the mean value.


Moreover if your design life is higher than quoted value from vendor then you will have to reduce the HDB following a linear relationship between HDB and design life on a log-log scale. Again you would need the applicable gradient value from the vendor.