Pressure testing is an important safety process that ensures your hydraulic systems operate safely, optimally, and efficiently.
Through hydraulic pressure testing, you can determine the minimum and maximum operating pressure. Besides, you can choose suitable accessories for your pressure systems.
What is Hydraulic Pressure Testing?
Hydraulic pressure test measures the integrity, strength, and reliability of the hydraulic system. It can be done on components such as; actuators, valves, tubing, fittings, pumps, and motors.
Importance of Knowing Pressure Rating
Pressure rating is the maximum allowable working pressure of hydraulic components.
The pressure rating of any fitting in the hydraulic system is usually based on the lowest pressure-rated fitting end. Therefore, the lowest rate working pressure of a component should be considered as the maximum working pressure.
For proper performance of the hydraulic system, the design and the pressure rating of each component of the hydraulic system should be put into consideration. That is, you must know the standard rating for tubing and hose components.
Pressure rating can be used as a safety measure to ensure the components can safely withstand the pressure they will encounter during their normal operations.
Benefits of Pressure Testing Hydraulic Systems
Some of the benefits of pressure testing include:
· Determining the Integrity and Strength of the System
Any weakness in the components of the hydraulic system will affect the overall performance of the system.
Therefore, pressure testing helps verify the structural integrity and fitness of components such as the hoses, tubing, actuators, and valves of the hydraulic system.
It provides a level of confidence that the system will withstand subjection to a corrosive environment without incurring any damage.
· Identifying Leaks on the System
Through pressure testing, leaks can be detected and addressed before they cause more significant concerns such as loss of fluids, potential safety hazards, and reduced efficiency of the system.
· Key Element for Quality Assurance
Pressure testing is used during the manufacturing process to identify defects in the hydraulic system before being put to use. This also helps to ensure the hydraulic system meets the safety standards put in place by various regulatory bodies.
· System Validation
Validating the performance of the system by ensuring the components and the entire system can withstand and work effectively under the intended pressure.
Hydraulic Pressure Testing Calculation
Calculating hydraulic pressure is important in determining the pressure that the hydraulic systems need to be subjected to.
To determine the hydraulic pressure, the following should be calculated first;
- System pump pressure
- Maximum working system pressure
- System static pressure
· System Pump Pressure
This is the pressure generated by the hydraulic pump during the system’s operation. You can measure this pressure in:
- Pounds per square inch (psi)
In case the pressure is not available in manufacturers’ systems documents, then you will have to calculate it yourself. You can use the formula below to calculate the system pump pressure.
Where; p= pressure
F= force applied
- The area through which the force is applied
Alternatively; the Pressure= flow rate is divided by the area through which the fluid flows
P= Q/ A
· System Static Pressure
When the hydraulic system is at rest, the pressure exerted by the hydraulic column is the static pressure.Many factors influence the static pressure such as:
- Type of fluid
- Height of the system
- Fluid density
You can calculate the system static pressure using the formula below:
p = ρ × g × h + p0
Where we have:
p = hydrostatic pressure
ρ = density of the fluid
g = gravitational acceleration
h = height of the water column
p0 = external pressure
· Maximum Working System Pressure
In this case, you will calculate the total pressure of the system. Remember, this may also involve situations where you are using the hydraulic system.
Calculated using the formulae;
Maximum Working System Pressure[MWSP]= SSP + SPP
SSP- system static pressure[Bar, Kpa, psi]
SPP- system pump pressure[Bar, Kpa, psi]
MWSP- maximum working system pressure[Bar, Kpa, psi]
From this, the hydraulic pressure test can then be calculated using;
HPT[Hydraulic pressure test]= MWSP x 1.5
Where; 1.5 is the standard value as per the BESA TR/6
Key Terms to Use in Hydraulic Pressure Testing
There are key terms used during hydraulic pressure testing that should be well understood, they include;
· Sectional Test
This involves testing each section of the hydraulic system separately.
Commonly done on large hydraulic systems where complete testing of the system once is not possible. These systems are split into smaller sections and pressure testing is done on each section.
· Testing Pressure
In situations where the pump is not running, the hydraulic system may exert a certain amount of pressure. It is this pressure that we call the testing pressure.
· Maximum Working Pressure
This is the maximum or total amount of pressure your system will exert when operating under normal circumstances.
It entails both the system pump pressure and the system static pressure.
· Valve-to-valve test
Testing is done on the valves of the hydraulic system either through the valves or to the back of the valve. Once the valve test is completed, the entire system is covered.
· Total System Pressure
This covers the entire system including all the equipment, joints, and pipework. It is the fastest way of pressure testing and it is completed after the cleaning stage of the onsite commissioning process and pipework flushing.
Strategies in Pressure Testing Hydraulic Systems
There are three major strategies in pressure testing;
· Sectional Pressure Test
This is a strategy that involves testing each section of the hydraulic system separately.
It is usually done on large systems where testing the whole system at once may not be possible. These systems are therefore split into smaller sections and pressure testing is done on each section.
· Full Circuit Pressure Test
This is the best strategy that involves pressure testing the whole hydraulic circuit.
It helps in determining the system’s strength, and integrity as well as identifying leaks and any other issues that may interfere with the performance of the hydraulic system.
· Valve to Valve Pressure Test
This strategy is similar to the sectional pressure test but in this case, it is done to the valves of the hydraulic system either through or to the back of the valve.
Once the valve test is completed, the entire system is covered.
Common Hydraulic Pressure Tests
Pressure tests are performed on the hydraulic system to determine the integrity, the strength, the reliability of the system and to identify leaks.
These tests are usually done before a new pressure system is put to use or after the repair of the existing system.
The most commonly used methods for pressure testing are;
- Non-destructive Hydrostatic Pressure Test
- Destructive Hydraulic Pressure Tests
Non-destructive Hydrostatic Pressure Test
This is the technique used to assess the performance and the integrity of the system by locating the surface and the subsurface defects, without causing damage to it.
Furthermore, this type of test is important in detecting leaks, and flaws while preserving the functionality of the hydraulic system.
Normally, during pressure testing, the hydraulic system is subjected to a higher pressure than the required operating pressure. Take, for example, a pressure that is 1.5 times higher than the required pressure. This pressure is usually designed by industry-specific standards.
If the hydraulic system is perfectly designed to meet the specifications and standards requirement, the system will successfully pass. That is, there will be no damage to the hydraulic system.
However, if the system has not been correctly designed or has defects then there is a possibility of the test being destructive.
Non-destructive test is the most popular and it is typically needed for the following reasons;
- Ensure reliability and safety of the component
- Ensure acceptance of a given specification/requirement
- Prevent accidents and the need for repairs.
- Reduce the cost and the unplanned facility shutdown.
- Give information on the repair criteria
- Identify defects in a component.
- Validate the design and the manufacturing process.
Destructive Hydraulic Pressure Test
This is a type of test that is used to determine the performance of the hydraulic system when subjected to different pressure levels.
It determines the pressure at which the system fails under pressure and through this, the designed operating pressure of the system can as well be established.
Destructive testing is usually used in quality control, the process of material qualification, and research development.
You can achieve this successfully through different methods and techniques:
· Bursting Test
Burst testing involves applying pressure to the component until it bursts. This helps in determining the maximum pressure that the component or the material can hold up before bursting.
· Creep Testing
Creep testing involves exerting a particular pressure on the system for an extended period. The test helps to determine the failure characteristics or deformations of the system under that applied pressure.
Apart from the two common hydraulic tests, there are other tests; the impulse tests and spray tests.
The spray test can be used to assess the corrosion resistance of the materials or components while the impulse tests predict the hose life.
Step-by-step in Hydraulic Pressure Testing
Hydraulic pressure testing is done using the pressure testing circuit which is made up of the following components;
- Hydraulic power pack
- Pressure testing materials such as valves, blank flanges, gauges, etc.
- Hydraulic power unit
The hydraulic power unit mainly fills the circuit with water or oil. On the other hand, a hydraulic power pack connects to the pressure line and pressurizes the circuit to the test pressure.
Pressure testing in the hydraulic system is done by:
Filling the Circuit with the Test Medium
The hydraulic pressure system is filled with appropriate test medium, either water or oil which is clean and free from contamination. The drain line and the return lines are separated from the others and pressure is increased to test the lines.
Applying Pressure to the Hydraulic Pressure Line
The hydraulic power pack pressurizes the line to the maximum desired level. The pressure is then held for approximately 15 minutes while verification for leaks and visual checks of fittings and flanges is being done.
At the same time, the pressure gauge which is mounted at the end of the pressure line is also monitored for pressure loss.
Releasing Pressure to the Pressure Line
Pressure is released from the pressure line through valves and this then allows more pressure to the drain and the return lines.
Pressurizing the Return and Drain Line to their Respective Test Pressures
Upon pressurization of the drain and return line, readings at the opposite end of the pressure line and at the manifolds are monitored. The drain valve is then opened to drain the line pressure after completing the test successfully.
Hydraulic Pressure Testing and Guidelines
Four guidelines can be referred to during pressure testing, they include;
- ASME Power Piping Code B31.1 [USA developed]
- ASME Process Piping Code B31.3 [USA developed]
- ASME Code for Pressure Piping B31.9 [USA developed]
- BESA TR/6 Site Pressure Testing of Pipework [UK developed]
Among these guidelines, BESA TR/6 is most commonly used in pressure testing, especially for different types of pipework. It gives the best information concerning the methods of testing and the requirements for the tests.
Can Hydrostatic Pressure Testing Damage Hydraulic Systems?
Yes, it is possible especially when done by engineers who are not well conversant with how the pressure testing is done/completed.
When can you use Hydraulic Pressure Testing without Pneumatic Pressure Testing?
The use of hydraulic pressure testing alone without pneumatic is possible and common.
However, it can only be done once the evaluation has been undertaken to ensure there are no risks in the surroundings.
In case there is any risk encountered during the evaluation, pneumatic should be used before the hydraulic testing is done.
Additionally, hydraulic pressure testing can be used alone when the hydraulic system being tested exclusively utilizes hydraulic fluid for its operations.
How long does the Hydraulic Pressure Testing Process Take?
The time required to complete pressure testing depends on the project requirements and the type of system to be tested.
For example, according to BESA, if heating the hydraulic system that has been installed using galvanized pipework, pressure testing can take approximately one hour.
In hydraulic pressure testing, the suitability of the system and it components is determined by carefully analyzing the test results and ensuring that they meet the specific quality standards and requirements.
Parts of Hydraulic System – Source: TARGET HYDRAULICS
Troubleshooting Hydraulic Power Pack – Source: TARGET HYDRAULICS
Pressure Test Procedures – Source: NATIONAL ACCELERATOR LAB
Hydrostatic Testing – Source: WIKIPEDIA