How to burst test safely, cleanly and with complete control

Proof testing versus burst testing: what is the difference?

It is important to decide what your objective is, as pressure or proof testing is not the same as burst testing.

Pressure testing

Pressure testing, proof testing or proof pressure testing: What should appear on my proof testing certificate?

In truth, these could be considered different names for the same thing.

Pressure testing will pressure or hydrostatically test a component up to a set “proof” test pressure. The designer or user will have set this, often based on a “safety factor” or multiple of the working pressure. Your end result will be a test certificate as to what was done and when.

If you look at a test certificate, it will state a medium, a pressure, and then go on to declare that on a certain date the part (whether it is a hose, pressure vessel or whatever) was taken up to the pressure with no leakage or permanent deformation. It is always useful to describe the part with a serial number if there is one. If you have no traceability on what you are testing, the certificate has little value both from a QA point of view or commercially. The certificate can be fairly general and just record these basics or there may be a procedure called up, this being your own internal procedure or based on an International Standard. If you have called up a pressure, we would expect this to be using a calibrated pressure gauge and you might call up the serial number and calibration details as well.

Burst Testing (or testing to destruction)

Burst testing is a different methodology. Here you are testing to destruction and getting some comfort from the multiple of the working pressure when failure takes place and also learning something about the mode of failure. It is no good building up a section during design only to find that you have missed a much lower pressure failure mode elsewhere. Alternatively, a designer might find that something is unnecessarily over-engineered and take a look at the design again. In a world of 3D modelling, it is extremely useful to back up theoretical failure modes and pressures with actual evidence.

The essentials of Burst Testing

Sarum Hydraulics Micropac pumps have been used throughout the world for easy burst testing for 30 years. What have we learnt over that time? We would focus on safety, “being in control” and productivity.

1. Safety is paramount.

In order to guarantee the safety of you and your staff when burst testing, you need a plan and safety procedures must be in place. As burst testing is inherently a sudden uncontrolled release of hydraulic energy, it is dangerous if not properly supervised. Ensure you have the skills and a plan as to how best go about safe burst testing.

2. Productivity

Our advice has always been that like any other testing, you can make it easy or difficult, productive or a very hard work. What do we mean? Time is money is a good start. What makes burst testing productive? Our five musts are;

Buying in the correct fittings to do the job easily and keeping them safe in a kit box
Standardising on a hose and fittings so the next job that comes along uses these parts.
Designing the test piece so you thought how you were going to test it, not leaving it until later and find there is a major project in making a connection.
Not cutting corners on the connections. There is nothing more frustrating than making a poor job of the pressure connection to the test piece and have it fail there.
Writing the results down and labelling the test piece in a business like manner. Scientists have lab books for very good reason!

3. Control

Control of the process is a paramount here at Sarum Hydraulics. You need to increase the pressure steadily. As such, we recommend using hand pumps as they allow the user to maintain total control over pressure exerted, with the option to stop manually at any given moment. An air driven pump can also work brilliantly provided you cut pulsations and are also able to cut the pressure flow immediately after burst. Probably the most important thing is to be able to accurately record the pressure at which it bursts. We are still “old school” and suggest using a drag pointer pressure gauge with a slave pointer that follows the main indicator and records the maximum pressure. The alternative is a digital pressure gauge that offers this peak facility. Ensure that the technician knows how to use the digital pressure gauge. Ashford Instrumentation would be our first port of call.

Ashford Carry Pointer Window

What happens when it fails or bursts?

Always remember there are a many modes of failure. You might just see a sudden weep, burst or extrusion from a seal, which sometimes is not very helpful. Often designers will deliberately enhance sealing to encourage the “next” thing to fail. If there is a more dramatic failure, you are into failure of materials such as barrels, diaphragms or rods rupturing or failing, complicated failures in mouldings or manifolds or even a hose or fitting failing. Engineers are interested in sources of failure and catastrophic failure is traditionally what they are trying to generate by burst testing. That said, if burst testing does highlight a troublesome sealing issue, then that can be a big win for product reliability or in-process failures on the line.

When do you need to burst test?

Designers may burst test very early in the design process to highlight failure modes, look for catastrophic failure and validate theoretical modes of failure and their pressures.

In gaining approval of a product, burst test results may need to be recorded in a Technical Construction file. Finally, in a production environment where special processes are involved or you are limited on what testing you can do, you may take a sample of units and burst test to destruction. That will give Quality Assurance comfort that there is consistency in a process.

What have we learnt?

The higher the volume in the system and the higher the pressure, the greater the energy that might be released. The PED (Pressure Equipment Directive) sets out that useful chart of volume, pressure and how hazardous the medium is. Think about what might fail. Is there any failure mode that could see parts with a mass shooting off a component? Thinking through failure mode is a priority. Safety is paramount, so make sure you and your staff are well protected should you be testing a particularly high volume application.

Containment is a necessity, not a choice. Any clear window should be polycarbonate or similar so that the material does not shatter. We recommend using some sort of box or chamber, which we have always found is the best arrangement for smaller components as it defines and contains your testing zone and minimises risk to property and staff – nobody wants debris ricocheting off walls or an area drenched with fluid!

Containment when burst testing is advised.

Can you test under water? On the face of it, that would deaden the shock of failure, but there is still an uncontrolled release of energy and still the risk of debris. Over the years, we have always used chambers.

Containment need not be complicated, although the moment you start to use electric or air driven power operated pressure pumps, it needs a proper interlock on the door. If one makes up a cabinet and there is a door, you could very probably make up some sort of interlock so it has to be shut before testing can begin. Interlocks don’t necessarily mean safety switches. A mechanical device that stops a pump from being operated or a ball valve lever that fouls the door when it is open can suffice if your system is non-electrical.

A pressure gauge that is not calibrated should not be used in burst testing or pressure testing.

The medium is also key. Gas is compressible, so for us is a no no. We like water, as it is cheap, safe and clean. Needless to say, any fluid that is inflammable or hazardous would not be our choice for safety reasons.

As with any testing, a log book and labelling is essential. Engineers will be able to interpret what they see in a failed component, but identifying it is a must. If burst testing is part of a qualification test, you are keeping this evidence for long periods, so you have to be sure.

You can spend a fortune on burst testing rigs. That may be justified if you are on high volume production. You can also make a well engineered burst test unit using Micropac water hand pumps up to 700 bar and a containment chamber.

Micropac ® Burst Test Pump

Sarum Hydraulics have been providing pressure and burst test know-how to customers for over 30 years. Our hydraulic hand pumps offer rugged and cost effective burst and pressure testing solutions. For our full range of handy hydraulic solutions, take a look at our website at www.sarum-hydraulics.co.uk

Disclaimer: The information and views expressed are personal from John Foster. Feel free to add to our knowledge database or correct me if there is something incorrect.

How to: Burst test safely, cleanly and with complete control.