Pressure rating on a tank return manifold 2

[Grunchy]

Good afternoon everyone,

There is a welded manifold fabricated from 1.5" square ERW tubing and half couplings, it is a collector of a number of case drain lines from some hydraulic pumps. The hoses come together to the manifold because there is a temperature gauge on each line for monitoring the condition of each pump, the manifold brings the gauges together so a person could monitor all the pumps easily from one place. The case drain lines all collect into the manifold which then dumps into the supply tank via a return filter. There is a steady stream of flow that keeps the manifold full, and the manifold is flooded anyway because it is mounted a couple feet below the level of the tank.

The problem is that one of this manifold had developed a pinhole leak, and in the resulting investigation it was determined that the manifold had not been given a pressure rating and therefore had no pressure test instruction. As I say this is a low flow-rate application mounted just a couple feet below fluid level, so while the collector is exposed to a constant pressure, it isn't exposed to much pressure.

I'm thinking of giving the collector a working pressure limit of say 100 psi and ask for a pressure test at time of fabrication of 1.5x working pressure (150 psi). It is a weldment constructed of 1.5" square HSS tubing and end caps with numerous in and out ports, the ports are just half couplings welded on. It doesn't lend itself to any standard pressure rating calculation, would FEA be appropriate for this?

What is your suggestion?

Thanks in advance.

 

[pennpiper]

Are you kidding????
Your using square tubing in a Pressure Piping situation, Are you NUTS!!!

Where is this facility? I want to make sure I don't pass it when I drive around.

prognosis: Lead or Lag

 

[Grunchy]

Hi, yes that would be bad. But seriously it is just a collector manifold that dumps into the supply tank, forgive me if I wasn't clear enough, the supply tank is at ambient pressure conditions.

If I was to make a guess what the collector manifold is pressurized up to, it might be as high as 10 psi or so.

 

[Duwe6]

ASME VIII Div 1 allows Proof Testing. Just do that, using a 4:1 safety factor. Hydro to 160 psig, and rate this 'problem child' at 40 psig, based on the proof load. Or 200# and 50#. And if anybody is afraid to hydro it to these pressures, scrap it and make one from SA-53 pressure piping material.

1.5 x hydro's are ONLY for items designed within the rules of ASME, and built using approved materials. A500 tube-steel is really 'nice' stuff to build with, but it has NEVER been allowed for pressure-retaining members of ASME or API boiler, vessel, tank, pipeline, etc.

 

[JStephen]

If you treat the flat side of that tubing as a fixed-fixed beam, calculate the moment and then the stress, that should be a pretty reasonable approximation. There are various grades of square tubing available, I think the most common is A500 Grade B, which has a yield stress of 42,000 or 46,000 or so- a little higher than A36, at any rate. If the calculated pressure comes up high, I'd probably lower it considerably anyway, just to allow for uncertainties in the grade and the construction. If it's subject to just a couple of psi, there's no real reason to rate it higher than 15 psi or so.

ASME Section VIII does have design data for rectangular vessels in one of the appendices, but that'd probably be overkill. They may also assume stiffeners at regular intervals.