Dorin Popescu FRP Allowable Stress - Intergraph CADWorx & Analysis

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17.3.2014 FRP allowable stress - Intergraph CADWorx & Analysis

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FRP allowable stress

CCMech

Member

Registered:12/04/09Posts: 17Loc: Canada

Hi all,

I got a datasheet from the supplier for the FRP piping.

It listed Axial Tensile Ultimate Stress and Axial

Compression Ultimate Stress.

Which one should I use for allowable stress?

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Re: FRP allowable stress [Re:CCMech]

Richard

Yee

Member

Registered:12/16/99Posts: 166Loc:Chesterfield,MO 63017

CCMech,

Consider using 10% of the axial tensile ultimate stress

as the Allowable Stress for FRP piping. The long term

pressure design of FRP pipe is based on the 10% of

UTS rupture stress.

A compressive stress resulting in buckling failure will

probably occur much sooner than a compressive stress

ultimate failure.

The real trick is in the details. Support attachments

must avoid point type loads that would damage the

glass fiber reinforcement of the FRP structural cage.

The big 'No-No' is U-bolt hangers that crush the

diameter of pipe. The FRP pipe should have saddle

plate and not sit on the edge of angle or channel

structural steel

_________________________

R Yee

Top


CCMech

Member


Thanks Richard.

The Axial Tensile Ultimate Stress given by the vendor

is 10.3KSI and the the Axial Compression Ultimate

Stress is 33ksi. Which one should I use?

Should they be the same?

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#44244 - 08/19/1112:56 PM

#44296 - 08/23/1102:58 PM

The elbow fails all the time even when I didn't use any

anchors just +Y supports. Can you tell me how to

model the elbows correctly?

Top


Richard

YeeMember

Registered:12/16/99Posts: 166Loc:Chesterfield,MO 63017

CCMech,

Pipe is usually applied for pressure service. Pressure in

pipe results in tensile stress. The magnitude of the

UTS is less than the UCS - could be reached first

before the UCS, in bending load cases. Use the tensile

UTS.

The reasons for tensile UTS being less magnitude than

compression ultimate stress are result of the way

strain is shared between the glass fibers and the

plastic resins. If the glass fibers are continuous (full

length) filament wound in the structural cage, then the

loads are sustained mostly by the glass fibers with the

UTS of the composite approaching the UTS of the

glass. If the glass fibers are shorter length chopped

strand or mat, then the plastic resins have the role of

connecting the glass fibers with the shear strength of

the plastic resins being a large component of the

composite strength. There is also the proportion of

glass fiber to the plastic resins in the composite that

determines the UTS and UCS.

Elbows are usually manufactured stronger than thestraight pipe, whether it is FRP or metal. If you are

using same properties for your elbows as for the FRP

pipe, then you might verify the elbows wall thickness

with the manfacturer. The manufacturer should also

provide guidelines for spacing of supports - the

recommended FRP spans are less than half that for

metal piping support spans.

_________________________

R Yee

Top


CCMech

Member


Hi Richcard,

If I use UTS as the allowable for BS 7159. Based on

the given rated pressure and the wall thickness by the

vendor, the calculated hoop stress is higher than UTS.

It failes for piping especially for the tees as the

combined stress includes the hoop stress. The Eh/Ea =
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#44315 - 08/24/1109:06 AM

1.83.

If use hydrostatic hoop design pressure(97.5MPa),

then the hoop stress is acceptable. How the piping

thickness is dertermined? If it is based on the hoop

design stress, should the axial stress be 97.5/1.83 =

53.3MPa?

Also, how the beam bending stress works?

Thanks,

Top


Dorin

Daniel

Popescu

Member

Registered:06/05/00Posts: 36Loc: MiddleEast

Hi, CCMech !

I've encountered the same problems on a recent

project.

My advice is: Unless the Project Design Specifications

(i.e. Basic Design, Piping Design, Piping Stress Analysis

etc .) do not clearly state the Design Code(s) for FRP

Piping, clarify as soon as possible with the FRP Piping

VENDOR which is the Design & Analysis Code for FRP

Piping.

Most probable, the design/analysis Codes may be

ASME B31.3 (Chapter VII - together with several ASTM

Standards - see the Code), BS 7159, UKOOA and, the

most recent and complete Code/Standard, ISO 14692(part 3 for design/analysis purpose). However, I

repeat, the design/standards code(s) are BASIC INPUT

DATA for FRP Piping design/stress analysis.

Once the FRP Piping analysis Code(s)/Standard(s) are

clarified, then ask the FRP Piping Vendor ALL the FRP

material properties' values addressed by the design

Code/Standard.

Be careful, Vendor may suggest as design/analysis

approach a mixture between different Codes/Standards

(see above) and other Vendor's ownstandards/specifications.

Most frequently, the piping flexibility analysis method

(i.e. stress calculation formulas, loading cases, SIF's

assessment) may follow one of the international codes

named above (BS 7159, UKOOA, ISO 14692), but the

allowable stress definition/assessment may be

accomplished in a different manner, by employing lower

safety coefficients and/or other methods that are not

provided by the Codes.

In this situation, try to impose/ask to Vendor to

guarantee officially (or to take the responsibility for)
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#44339 - 08/24/1104:41 PM

#44347 - 08/24/1107:13 PM

the allowable stress values under discussion.

Temperature influence, loading-unloading cycles'

number, FRP pipe design lifetime and working fluid's

corrosion effects should be also taken into account.

Generally, a "clean" or "proper" design approach should

follow a coherent set of rules, meaning that one single

Code/Standard's requirements should be followed, from

the allowable stress definition/establishment up to pipe

loading philosophy, stress computation, SIF'sassessment and Code Stress qualification.

Best regards,

_________________________

Dorin Daniel Popescu

Lead Piping Stress Engineer

Top


CCMech

Member


Thanks Dorin.

I have asked the vendor all those questions, but I

don't get a answer from yet.

So for ISO 14692, are the vendor supposed to provide

all the parameters or they can be found based on the

hydrostat ic design stress?

Top


Richard

Yee

Member

Registered:12/16/99Posts: 166Loc:

Chesterfield,MO 63017

CCMech,

Have not applied BS 7159 for design of FRP piping. I

finally did the conversion from metric 97.5 MPa, and it

is 14,141 psi. !!! (975 bar )

Maybe the hydrostatic design pressure is beingconfused with the tensile design stress. Both have the

same units of force divided by the area. I would not

put 14,141 psi pressure into FRP pipe or even metal

pipe. Some small metal tubing size 0.50 inch or less

could sustain that high pressure.

You might need some more perspective and experience

of pressure design. The question of which design code

to use also implies different methods and

considerations and simplifications are made by the

different codes.
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#44355 - 08/25/1106:12 AM

The question of 'how beam bending stress works' will

be answered by an example beam with simply

supported ends over a 6 meter span. The beam

deflects downward at center of span due to weight.

Four questions to you:

1) Where is the maximum tensile stress?

2) Where is the maximum compressive stress?

3) Where are the tensile and compressive stresses

both zero?4) Where is the maximum shear stress?

Answers -

1) bottom of cross section

2) top of cross section, and equal magnitude for

symmetrical section

3) center of cross section (neutral axis, if not

symmetrical section)

4) center of cross section (neutral axis, if not

symmetrical section)

Now where does the piping design go to next? Thereare pressure hoop and axial stresses and bending

stresses occurring simultaneously.

_________________________

R Yee

Top


Dorin

Daniel

Popescu

Member

Registered:06/05/00Posts: 36Loc: MiddleEast

CCMech,

If ISO 14692 is the FRP piping design/analysis code,

then the Vendor should provide ALL the input

parameters' values in order to define completely the

FRP material failure envelope.

ISO 14692 Part 2 (16492-2) provides a complex set of

FRP material testing & qualification procedures. Based

upon these procedures, ISO 14692 Part 3 (ISO 14692-

3) details the FRP piping design procedures, including

the FRP material failure envelope definition.

If you have not worked with ISO 14692 Standards

before, please see for details ISO 14692-2, Section 6

(Qualification Programme)and ISO 14692-3 entirely. An

important detail, for a beginner, ISO 14692 Part 1 (ISO

14692-1) contains all the terminology definitions

employed by ISO 14692 standards.

So, if FRP piping for your Project is to be designed,

manufactured and tested in accordance with ISO

14692, then you have to get (from Vendor, of course)
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ALL the input parameters that define FRP material

failure envelope (see ISO 14692-3, Section 7.11).

Regarding the hydrostatic design stress, it depends

what hydrostatic test data you've got from the

Vendor: have you got the Short-Term Hydrostatic

Pressure STHP (and the corresponding short-term

hydrostatic hoop strength STHS), determined in

accordance with ASTM D 1599, OR the Long-Term

Hydrostatic Pressure LTHP (and the correspondinglong-term hydrostatic hoop strength LTHS),

determined in accordance with ASTM D 2992 ?

For ISO 14692, the basic strength parameters are the

Qualified Pressure "pq" and the corresponding Qualified

Stress "sigma qs", which are established in relation

with above LTHP (ASTM D 2992, procedure B) - see

ISO 14692-2, Section 6.2.3.1. "pq" corresponds to 20

years lifetime, working temperature not higher than 65

C Deg, neutral working fluid and unrestrained-ends

plain pipe loading (i.e. 2:1 pressure loading in hoop and

axial direct ions).

Depending on the actual piping loading regime

(temperature, lifetime, loading-unloading cycles,

corrosive working fluid), ISO 14692 provides

appropriate de-rating and correction factors.

Definitely, VENDOR should be consulted regarding

these evaluations.

If the short-term hydrostatic test strengths are

employed (i.e. the above STHP and STHS, as per

ASTM D 1599), then a scale factor "fscale" should be

used to perform the transition from the short-termstrength parameters (i.e. short-term failure envelope)

towards the long-term strength parameters (i.e. long-

term failure envelope) - see ISO 14692-3, Section

7.11. In this case, VENDOR should provide "fscale"

parameter.

So, to conclude, FRP piping analysis may be performed

exclusively in accordance with ISO 14692, ONLY IF FRP

Piping Material is designed, manufactured, tested and

qualified in accordance with ISO 14692 provisions.

If the above condition is not satisfied, then you should

establish TOGETHER with FRP piping VENDOR the

specific analysis approach. However, as I previously

noted, Vendor must take the responsibility for the

allowable stress values if the flexibility analysis does

not follow coherently a recognized international code

provisions.

Best Regards,


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Hop to: CAESAR II Go

_________________________

Dorin Daniel Popescu

Lead Piping Stress Engineer

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Dorin Popescu FRP Allowable Stress - Intergraph CADWorx & Analysis