Hydro records

[JonRiley56]

All,

I hope to set up to run a hydro on my boiler tomorrow or Sunday. I am ok with the procedure. What I am not clear on is what I need to do to "record" the event. Do I need to have video or pictures with something dated so I have proof if I go to a meet that it has been done ?

jon

[Lopez Mike]

I don't know about other areas but here in the Northwest U.S. any hydro you do without a designated club witness is for your own peace of mind. Not an inconsiderable thing! I hydro my various boilers almost any time I disturb the piping just to check for leaks.

The Northwest Steam Society has an appointed Safety Committee and any member of that committee can observe a hydro test and issue a certificate good for the rest of the year. Or twelve months. I honestly don't know which.

As far as I know there is always at least one committee member at each of our club events. My safety pops at 150 so I hydro to 225. I don't think it places any serious strain on the boiler. I wouldn't be nervous about leaving it at 225 under hydro for any length of time. I'm way, way below the yield point of any part of the system at that pressure.

On a related issue, it is instructive to note that on a fire tube boiler where the tubes are under compression rather than tension, the tensile strength of the material doesn't appear in the formula. The only property of the material that is considered is the modulus of elasticity.
One assumes that submarine designers know this well!

[fredrosse]

Mike wrote: "On a related issue, it is instructive to note that on a fire tube boiler where the tubes are under compression rather than tension, the tensile strength of the material doesn't appear in the formula. The only property of the material that is considered is the modulus of elasticity. One assumes that submarine designers know this well!"

I just looked up the ASME Code Calculations for the Margaret S VFT Boiler, and the Code Calculations do take into account the tensile yield strength of the tube material. The yield stress is not explicitly in the formulas, but various different charts/graphs are to be applied according to the yield stress and type of material for the tubes (or furnace under external pressure). When a cylindrical pressure part fails under external pressure, the material actually yields in tension, not compression. The attached figure is one of many in the ASME Code. Buckling column stress technology is applied here, and I think you have to be something like a "rocket scientist" to understand that stuff.

I worked at Electric Boat Division of General Dynamics for more than 3 years, where they built US Nuclear submarines. I can assure you these hulls were made of steels that have the same modulus of elasticity as ordinary low carbon steel, but these hull steels had yield strength very far different from the yield strength of ordinary low carbon steel.

[Lopez Mike]

Thanks Fred. I stand corrected.

I have a set of formula that are used by the live steam locomotive set in calculating margins for these little boilers and the modulus and dimensions are all that is included.

I was under the impression from these equations that until the tubes were deformed enough to get out of a circle (Euler failure?) that the modulus was the critical path.

It is comforting to me to know that the boilers I've encountered in this hobby have all been designed with very adequate margins. I worry about people getting finger burns and squashing a finger between a boat and a dock but not about an explosion.

I have an ultrasonic thickness gauge and so far, I have not found a problem in any of the units we've looked at around here. Even one rather ancient donkey boiler!

[barts]

The reason that yield strength doesn't matter for some geometries is indeed that as the part flexes, the loads increase dramatically. A good example is when standing on a aluminum soda can a very slight (elastic) deflection caused by gently pressing on the side of the can causes the can to collapse. Once the geometry of the configuration is disturbed even slightly from the equilibrium position, failure is inevitable regardless of material yield strength.

- Bart

[artemis]

...The Northwest Steam Society has an appointed Safety Committee and any member of that committee can observe a hydro test and issue a certificate good for the rest of the year. Or twelve months. I honestly don't know which...

one year from the date "witnessed". NWSS Safety Committee Member

[farmerden]

There's nothing wrong with keeping a log of what 's been done to your boat.Boiler check,fire extinguishers,equipment failures, modifications etc. When I bought my boat it came with a log indicating all trips,breakdowns,fixes,everything.When I had my own log truck ,everything was written down, right down to replacing lightbulbs! Was it the law? I dunno-but it made good sense to me and if someone questions you,there it is all dated and recorded! If you are in an area where you can't have a witness -so be it. Safety first and remember -you are closest to the boiler!!

[S. Weaver]

I second Den's counsel: every proper vessel has an engineering log. I can still hear the Chief's booming, sonorous voice: "Did you write it up in the log?"

[drhitch]

Steamers,
something tied to doing hydro testing.....

Under normal conditions, the feedwater chain-driven pump forces water back into the boiler from the hotwell. There is a checkvalve and a ball valve at the inlet of the boiler. If left closed, the feedwater pump builds up too much pressure and in one case, the pressure cracked the case of my feedwater preheat heat exchanger (a commercial oil cooler on the steam exhaust hose).

So, for hydro testing using the manual feedwater pump, I have shaped a copper bypass line around that (now invaluable) heat exchanger so as to avoid a blowout again....Does this make sense? Or am I too worried about forcing 200+ PSI through the system including the copper lines and that heat exchanger.

[fredrosse]

The rules of steam plant design dictate that, if overpressure is possible due to closing a valve, then relief protection must be provided for the piping and pressure vessels potentially exposed to high pressure. Any engine driven reciprocating pump that can have its discharge path isolated, should have a relief valve. Same rule for a manual pump if it can put out pressure in excess of the piping design pressure. The only exception to this rule is if the pump is somehow not capable of overpressurizing the piping.