Hydraulics :

Piping specs and Safety

The pressure ratings I posted yesterday came from a reference commonly used in the hydraulic industry and were stated for ASTM A53 welded and seamless pipe. Looking in other references and texts today, I find different burst pressures for seamless pipe. Since the majority of the references call for the higher pressures for seamless, I will post those here. Each person must decide what factor of safety they want to use. What I do for myself may not be the same as what you will want to do. There are MANY factors that affect the pressure rating of pipe. I suggest, as I did yesterday, that an informed individual uses at least a 6 to 1 factor of safety on burst pressure for properly installed new pipe. Below are the numbers that have two good references in agreement. These would be 6 to 1 on the stated burst pressure for ASTM A53 grade B SEAMLESS and ASTM A106 grade B which is also seamless. Note that welded pipe will have lower pressure capability.

1/2" ASTM A53 grade B type S and ASTM A106 grade B schedule 40 2600 psi

3/4" ASTM A53 grade B type S and ASTM A106 grade B schedule 40 2150 psi

1/2" ASTM A53 grade B type S and ASTM A106 grade B schedule 80 3500 psi

3/4" ASTM A53 grade B type S and ASTM A106 grade B schedule 80 2933 psi

All good pipe is identified on the outside of the pipe. Usually with a paint or ink marking. ASTM is the most recognized pipe spec. Any pipe not identified on the outside or not readable should NOT be used for hydraulics. There are pipe size tubings out there that are real junk and will not hold pressure. Some are sold in home centers as pipe.

ASTM A53 covers both welded and seamless black and galvanized pipe. ASTM A106 is only seamless and usually for high temp service, but it can be used for hydraulic systems. The grade identifies the minimum strength of the pipe material. You want at least grade B. Grade A is lower strength.

There are also API specs. API 5/L Grade B is very similar to A53 Grade B type S. API 5/LX is stronger and better.

Pipe may be rated and marked for more than one spec.

Again, you must educate yourself. Don�t in any way think that you can say �Well I found this on the internet and this must be OK� You can�t do that because you have not explained in detail how you are doing other things that have a very big impact on the pressure rating of the pipe. The list is very long.

- Tony - Monday, 03/28/05 12:15:23 EST

A safety note on hydraulic presses used to forge. Please remember that a pin hole leak of hydraulic oil if it impacts the hot metal will make a flamethrower. Please use a fire resistant fluid, such as a water/glycol, or polygycol fluid. These fluids, if maintained at the correct water content are very fire resistant. Please consider the hoses on the machine and replace at any signs of damage. It is a good idea to avoid hoses and instead pipe with a good grade of hydraulic pipe such as seamless schedule 80. I work in the forging industry, and have for 24 years. For 21 years of that I worked for a valve and fitting maker that supplied the heavy hydraulic press trade. I have seen the results of pinhole leaks in oil systems on forging equipment, and it is not pretty.

ptree - Saturday, 03/26/05 15:35:16 EST

Please note that in my previous post I suggested schedule 80 seamless, and in past posts forged steel fittings. I have indeed seen several injuries from injection of htdraulic oil and hydro test water. Also air paint gun injection. All had an unhappy side effect, and that was the injection of huge amounts of bacteria with ulgy results. The paint gun injection resulted from the removal of the guard, and when injected cost the man most of his hand.

I normally reccomend schedule 80 up to about 3000 psi, and then go to schedule 160. At 10,000 and above I suggest the move to a coned and threaded system. I have worked at pressures up to 30,000psi with the trheaded and coned system. By the way, The velocity in a pin hole is fierce, but the liquid pressure remains the same. I have heard that the injection machines used for needle-less medical innoculations work at 2800 psi. As many hydraulic systems operate at 3000 psi these days the injunction to guard against pinholes is very valid. Last time I made that warning I was accused of being afraid of hydraulics. Worked every day with them for over 20 years. Afraid? No Respectfull? Yes.

ptree - Sunday, 03/27/05 11:57:01 EST

Ptree, Obviously, we agree that care should be taken in the design and construction of hydraulic forging systems. Regarding plannning for failure and knowing the risks, we also obviously agree that it should be done.

We may not agree on how to plan and build.

While your cautions are good and correct, your hydraulic posts can be read as "don't do it". I'd rather educate on how it CAN be done. Hydraulics is a great tool. A hydraulic forging press is FAR safer than a power hammer of ANY variety. Much more controlled and slower motion results in less flying iron and more time to get out of the way. A hydraulic forging press is not right for all work.

There are ways to be safe with hydraulics and they are not rocket science or costly. The hoses and connections on my forging press are on the other side of the press from me. If a hose, connection or pipe leaks, it will not spray on me. THIS is the correct way to guard against a fluid injection. Another safety risk is not replacing things until they leak. That's asking for trouble.

While I frequently design for 8000 psi at the request of customers, I do not recommend high pressure for most industrial applications. Anything over 2500 psi is "high pressure" to me. More energy is wasted with higher pressures and there is, as we are discussing, many safety concerns. High pressure is required in aircraft for light weight and small component size. Some mobile equipment also benefits from high pressure hydraulics. There is no real need for high pressure hydraulics for the average forging press. Sure, the component size will be a little bigger, but there will be less noise, less heat, far less maintenance, far more safety and less energy use with lower pressure hydraulics. But we must always have more. We must be up to date. We must have the latest. That is another common misconception in hydraulics. 1500 psi is a good number for a forging press of the size we are taling about in my book.

Want to most effectively guard against pinhole leaks? Use lower pressure and keep the human away from the unlikely leak. And maintain the system! NEVER reuse an o-ring or seal. Keep it clean. Replace components when they show wear. Do you replace your tires when they go flat?

The only safe way to do something is to understand what you are working with. YOUR Education is the only true safety measure you can rely on. Cautions are not adequate. If you rely on others, you will be much more likely to get hurt. If you work with something that can hurt you and don't ask about it or don't understand it, you are proving Darwin correct.

If you assume a factor of safety of 6 to 1 for pipe, which is a hydraulic industry minimum standard, schedule 80 above 1/8" pipe size is not thick enough for 3000 psi. Most of the hydraulic work we are talking about is with 1/2" to 3/4' pipe size. Schedule 80 1/2" is 2300 psi for 6 to 1 and 3/4" schedule 80 is 1950 psi. Schedule 160 3/4" is 2780 psi for 6 to 1.

What conduits were you using for 10,000 and 30,000 psi?

The absolute "hydraulics leak, period", like all absolutes, is rediculous. Same with "a pin hole leak of hydraulic oil if it impacts the hot metal will make a flamethrower". The reality is that most of the time, IF a small stream hits the usual home shop (small) piece of hot iron, it will hiss and spit, but the oil will quench the iron. CAN there be vaporization and flamethrower like activity, yes. But I know of no occurrances like that. I'm not saying you haven't seen it. I'm saying they are very rare. You fail to mention how rare and that is misleading. Most of us are working with pieces of iron that are much smaller and do not hold enough heat to cause a fire. We are in far more danger of a quench oil fire or burn than a hydraulic oil fire. There can be no flamethrower like activity unless the oil is above it's flash point and there is sufficient oxygenation of the stream of oil.

None of the oil hydraulic equipment I have built or rebuilt, leaks. Accepting leaks is not necessary. If it leaks, someone selected the wrong components or the quality of the components and/or installation is bad. Or the parts are worn. This is common, but does not need to be accepted. "Hydraulics leak" is incorrect. The biggest culprit (after poor installation or maintenance) leading to "hydraulics leak" is tapered pipe fittings. Pipe fittings have no place in a hydraulic system any more. I use them at home when I am mating to an old system or using salvaged components (which is often, grin). With the right quality, techinques and sealants, pipe fittings can work, but are not recommended. SAE o-ring ports, flare fittings, and o-ring face seal fittings are far better. And frequently no more expensive as we have discussed before.

Fire resistant fluids require a significant step up in education. The downsides are sometimes higher toxicity, certainly higher purchase operating and maintenance costs for the fluid, and usually much higher maintenance costs for the equipment. IF used properly, they are safer around hot metal from a fire standpoint. Which is safer from an injection standpoint? The various fire resistant fluids or oil?

I'll stand by my recommendation to use oil and use it wisely for the average small or home shop. We can disagree on that.

As we're discussing this, I'm trying to think of a safe activity. Laying on the couch definitely kills you. Any activity I can think of, that results in accomplishment, has some risk. I can only think of one activity that is "safe". You get enjoyment, give enjoyment, and can get some good exercise. Even that has been known to kill people. But hey, if you die that way, you might well consider yourself a lucky man. Grin. Or woman.

- Tony - Sunday, 03/27/05 19:30:58 EST

Tony,
I used swaglok mostly in the 1/2" size up to about 10,000 psi and as stated coned and threaded tubing above.One brand is Autoclave Engineers. Another in High Pressure Equipment. For the swaglow I used stainless steel tubing, seamless, in 0.095 wall. Used both in 3 shift a day, cyclic hydro test, with a pressure test cycle about every 45 seconds. The schedule piping was a for home use and I will review the tables for the seamless pipe because I do not recall the ratings you list.

I do not reccomend against hydraulics use. Far from it. Just as you, I reccommend that care and prudence be used. I have worked around industrial equipment since 1978. I have seen hydraulics from the USA, England, Germany, Italy, and Japan. I have seen every fitting style and type. Yes, use new o-rings, but people don't. Don't use tapered pipe thread, but people do. Don't seal pipe thread with tape, but people do. Don't underbuild, but people do. In those years, i worked in R & D labs testing some of the very fittings and systems you mention as leak free. And again I stand pat, hydraulics leak. Not a question of if, but rather when and where. I have seen very high class maintnance and he things oozed, hoses failed, tubing cracked etc. Aluminum manifolds fatiqued and cracked and leaked. polygylcol more toxic than oil? enough, on to other things.

ptree - Sunday, 03/27/05 19:56:44 EST

References and Links

Alphabet Soup What's that acronym?
MACHINERY'S HANDBOOK, Industrial Press
Don Fogg Custom Knives

2005 Jock Dempsey, www.anvilfire.com