Fatigue Test ( Cyclic Oressure Test ) As Per EN1251

Vent the pressure between peaks.

This to release the possible trapped air in the system line?

Make sure there is no air (or other gas) present.

How does the testing rig work? There ought to be some sort of stroke adjustments for min/max pressure.

The purpose of having a standard is so that equipment from different makers meets a basic quality level before it is allowed onto the European market. If you were permitted to deviate on pressure, your competitors could deviate on cycles, say 10 instead of 10,000. They could market their product to EN1251 at a cheaper price. You lose your market, the customer gets ripped off, and your competitor is laughing all the way to the bank.

Can you deviate, NO, fix your pressure tester!

Thank you very much for the valuable inputs that received form everybody. As you said there is no meaning to seek for a deviation.

Iam just going to the facility provider to check for possibility to get atmospheric pressure during the down cycle. I assume that there should be a setting / valve available in the return line to control the flow of hydraulic fluid. I believe that the flow is the culprit.

I will come back after solving this.

Thanks N regards,

What is the reason it cannot go to lower pressures ? How do you make your test ? What kind of test bench do you have ?

It is in fact possible either only mechanical or hydraulic to make a test bench working according to the spec.

The required cycle is pulsating with an asymmetry factor R=min/max =0. If you change the min value the asymmetry >0 and the material is less fatigued. Your test will not supply the required life expectancy if R>0.

Thank you very much for the valuable inputs that received form everybody. As you said there is no meaning to seek for a deviation.

Iam just going to the facility provider to check for possibility to get atmospheric pressure during the down cycle. I assume that there should be a setting / valve available in the return line to control the flow of hydraulic fluid. I believe that the flow is the culprit.

I will come back after solving this.

Thanks N regards,

Dear friends,

Yesterday, we inspected the fatigue test equipment that available with our service provider. But the system cannot go to atmospheric pressure during down cycle ( it can go to 15Kg/cm2 only). So, we are going to buy a system suitable for the test.

We understand from our service provider that, hydraulic oil is used for this test normally all. But, as EN1251 is not insisting to use hydraulic oil, I wanted to use water for this test ( because it is cheaper). But is there any disadvantage of using water for such test? As far as the product is concerned, it is of SS304 material and after test, this cylinder is not going to put for any service. So, there is no issue of contamination etc.

So, what will be your opinion dear friends? Can I go ahead with water for testing - instead of oil?

I don't think that water versus oil is your problem. Properly functioning test equipment should be able to handle either. Gas in your setup has not yet been ruled out. If everything is truly hydraulic, this is only a matter of stroke adjustment. This entails larger machines for testing larger vessel volumes; maybe you are running into an issue on that score.

"Gas in the set up" means an air lock / trapped air?

How do you generate the pressure and how do you regulate its variation ?

Can you send a schematic of this "hydraulic" part ?

How is the cycle pressure versus time ? Which is the rise and fall velocity in MPa/s if it is specified ?

If you use valves for the pressure control then water will cavitate a lot more than oil and you can have even early control edge destruction and loss of true control.

Dear jhhassociates ans Tornado,

Further to discussion, i approached one manufacturer and could get a quotation / offer of fatigue test machine. As per them, water is used to conduct fatigue test and the temperature of cylinder will not exceed above 50 degree Celsius. Even if the temperature is increased, there is a system in the machine to stop the cycle automatically and can be restarted after cool down the cylinder. ( My cylinder test pressure is 34bar, volume is 200 ltr, material of construction is stainless steel and the thickness is 3.5 mm).

Now the person who is going to witness this test is asking to use hydraulic oil for pressurising the cylinder. And he is also asking for test uninterrupted trough out the 10,000 cycles .

My difficulty is, EN1251 is not giving any detailed test parameters ( referring to EN1251 clause 4.4.3.1) So, how i can reciprocate with the argument of the person who is going to witness the test?

I wanted to know whether EN1251 is giving a freedom to decide this or anywhere it refers about the detailed parameters of this fatigue test? I tried to locate in EN1251 but failed.

Hope help from CR4

I will reply first to the request to use hydraulic oil. There is a danger when using water for this test that the temperature could rise above 100ºC, especially if the cooling circuit malfunctions. While your test cylinder may be capable of withstanding any steam pressure generated, it is unlikely that a component only being tested to 213psi. or the connector attaching that component is capable of withstanding the high pressures that could be generated. The request to use hydraulic oil is therefore likely to be on safety grounds and should if possible be met.

Uninterrupted testing is more problematic. If the component contains a plastic or rubber seal or membrane that flexes during the test then this is a valid request. Such membranes will work harden if left to set, even for a short period, after repeated flexing and this would invalidate the results. (probably causing premature failure prior to completion of the testing). If there is no plastic, rubber or flexing membranes within the component, then you have grounds to challenge the requirement for a continuous test. Continuous tests are the norm but are not obligatory, and are often impractical if your factory does not work 24hr days.

Will your cylinder work with water or oil ? The fatigue test is not only for the tube but also for the seals. Not all seals work the same with both fluids. Oil would reduce friction and decrease temperature since the temperature rise is due to all losses in the hydraulic circuit and in the cylider itself.

The best is to do the test with the working fluid. In both cases the pressure generator should be equiped with a cooling unit in order to maintain the fluid at a constant temperature.

Which are the dimensions of your cylinder I have the feeling that it can be discrepancy between pressure level and wall thickness ?

Is it a cylinder witha piston or only a cylidrical reservoir ?

Dear Jhhassociates,

Thanks for the guidance. I could understand this as :

1) Hydraulic oils is better but if Iam confident that the temperature will not raise above 50 degree Celsius, i can use water.

2)Continuous test is compulsory if the test cylinder is having any rubber component. As my test object is not having any rubber component , i can make interruption - in unavoidable circumstances ( like power failure, temperature rise above 50 degree Celsius etc.)

Now I wish to ask whether a detailed parameters / procedure is available in EN std or in any other std so that i can link and use that as reference or base?

Type "code of practice pressure testing" into your computer search engine. Choose the CP that best matches your application.

Dear Nick Name,

My clarifications as follows:

1: My test cylinder is OK for both oil and water

2: It is a simple cylinder having diameter of 450 mm, height of 1400 mm aprox and a wall thickness of 3.5mm and dished end thickness of 4 mm . All stainless steel 304 material.

3: It is not fitted with any rubber component. No component other than stainless steel.

4: Our design engineer confirmed that it is OK for the test.