one pipe is running at 20 metre height in pipe rack.so,i analysed with wind condition and forwarded the loads to structural people.but they are telling give the operating load only.don't give the loads with wind,because while doing structure design,we also considering wind load.
what i have to do?advice me.

You need to determine how they arrive at their wind load. If your structural department is just estimating the wind load on the pipe, your numbers are better than theirs, especially regarding the distribution of the load to the pipe supports.

If they already consider the load, you don't want to "double-dip". Just make sure everyone is in agreement with the load magnitude and its distribution.

Further to Ray's reply, I would like to add the following points.

Structural group is mainly concerned with effect of wind on the structure with the imposed dead wts.,which is known as structural sway.

Pipe stress programme analysis the load on the pipe due to wind, considering that there is no wind movement on the structure supporting the pipe unless the user specifically specifies sway movements at the supports via connecting node.

In my opinion unless a common analysis, by that I mean wind analysis with sway is not considered , the wind analysis holds little value for metal pipes .

There can be substantial difference in the loads arrived by these two methodologies. At that point , things can be discussed with structural group to arrive at the most reasiltic and economical design.

There can be high loads particularly at points where there is substantial difference in movements between the pipe ( due to some restraint , like when the pipe is entering the rack from some vessel) and that of the supporting structure due to sway or for a pipe connected to two structures with different sway behaviors, like psuedostatic seismic anchor behavior something which the structural guy probably will not consider.

A.Bhattacharya

Stress Analyst

Bechtel Corporation

I am going to be surprised if the sway of the supporting structure causes that much difference in the wind load picked up by the piping.

If this is a major concern, model the structure and perform a combined analysis.

When a pipe is entering a vessel from a pipe rack, due to wind deflection or sway of rack structure, simulated by sway movements at cnode of support point, load at equipment nozzle can increase. If we perform WRC-107/297 analysis at the nozzle, which way this additional wind sway load will have to be classified - sustained, ocassional or expansion - as this load is secondary in nature, will it be included in expansion or will it be included in ocassional ?

regards,

sam

I would say this is occasional.

This is not an expansion load as it is not self-limiting. When wind hits the pipe rack it puts load on the nozzle. Local yielding at the vessel-nozzle junction will not relieve the stress in the pipe rack.

It is not sustained because it is caused by an occasional event.

B31.3 - Paragraph 302.3.6

"(a) Operation. The sum of the longitudinal stresses due to sustained loads, such as pressure and weight, and of the stresses produced by occasional loads, such as wind and earthquake..."

Many of the answers are in the Codes, if you look. If there was a shortcut, we would have made it SOP by now. Always remember the first rule of pipe stress analysis. "If it was easy, it would pay minimum wage."

Primary stresses are those produced by phenomena that will not abate if the pipe yields locally. These phenomena include pressure, weight, wind, earthquake, impact forces (including water hammer), snow and ice load, etc.

Secondary stresses are those created in the piping by the application of loads which will abate if the pipe yields locally. These typically include displacements imposed by thermal growth or by terminal point displacements of low magnitude.

Hello all,

(Surprise) We had this conversation a few months ago. Occasional loads and sustained loads are always going to be primary. Wind can be a sustained load as it is at the refinery in Aruba where there is a CONSTANT 20 to 30 MPH wind from east to west 24/7. The occasional wind at that refinery would be the 25 year 50 to 60 MPH wind as the storm goes north of the island (they have never been hit directly by a hurricane). Some "unaware" design firm designed a stack for one of the process units in Aruba and did not get the "spoilers" right - the stack moved perpendicular to the wind direction 24 inches in each direction until smarter people fixed it. It was quite a sight for a while though.

I knew that wind as occasional load is a primary load.

But, my justification was that wind sway is displacement induced load - so, can be called secondary load like SAM(seismic anchor movement).
As allowable load for thermal expansion is more, it could be easier for piping analyst to qualify vessel nozzle load, if the wind sway loads were included in thermal expansion, as we did in Sec-III NC/ND codes for SAM in nuclear piping sometimes.

Moreover, an appreciable wind sway of rack structure can occur only in extreme scenario.

regards,

sam

Yes, wind load is a primary load and can cause collapse but in this case where the wind load causes the deflection of a structure (the vessel) that "supports" the piping AND if I assume that the piping cannot alter that deflection, then my concern would focus on the possible fatigue failure of the system - a secondary evaluation. But don't rely on a higher allowable in SA over Sh. If you start counting cycles your f will get pretty low.