Modern Hydrostatic Testing Methods in Refinery Equipment 

1 Introduction

When looking for pressure testing services, oil and gas refineries encounter a lot of uncertainty. Pressure testing is critical for safe and efficient industrial products manufacture, refinement, storage, and transportation. Inappropriate practices put a company’s production and financial soundness in danger. Hydrostatic testing alleviates a lot of safety concerns and testing failure hazards related to traditional hydrostatic testing methods.[1]

Hydrostatic or hydro testing is the most common type of leak testing for pipe systems, gas cylinders, boilers, fuel tanks, etc. Hydrostatic testing can be carried out in several different methods. All approaches require draining the contents and flooding them with water to generate a static pressure at or above the system’s normal operating pressure. The equipment is checked for visible and/or measurable leaks and deformation. Certain hydrostatic testing services increase the accuracy of visual assessment during this operation by adding fluorescence or traceable dyes to the water in the system. This procedure allows experts to detect a variety of problems. Existing material seam defects, linear anomalies, stress corrosion cracking, active corroding cells, and poor welding are the most common. Hydrostatic testing entails the advantage of providing a degree of confidence in the system’s integrity because it nearly usually entails pressurising the line or vessel over normal operating pressure. Pipes and other equipment should be inspected before the hydrostatic testing, if feasible, to decrease the chance of testing failure.

2 Hydrostatic testing in refineries

According to federal regulatory requirements, hydrostatic testing is a well-planned and regulated process that allows you to validate a threshold measurement for safe operations. A hydrostatic test is conducted on all new pipeline construction before it is put into service. It can also be done on existing pipelines to ensure pipeline integrity and shipping capacity.

As part of routine operations, water coloured with a water-soluble, biodegradable green dye is injected into the pipe between batches of oil being carried. Urethane cylinders separate and seal the water and oil, after which the batch is transported through the line until it reaches the designated pipe section for testing.

The pressure on the tested section is then increased to achieve and maintain the required test levels and duration. If water leaks during the test, the source is discovered, and the damaged part is fixed and retested. Water may spray into the air or pool on the ground if there is a water release during the test.

The section of pipeline under pressure is patrolled by aircraft and on foot during the testing procedure. Computer data programs are used to keep track of pressures.

The water is then carried down the pipeline to a plant, generally stored in a tank at one of our terminals. According to municipal, state, and federal rules and/or environmental permits, the water is cleaned, processed, and disposed of.

Internal pipeline inspections with “smart pigs” give more information about the pipeline’s condition while eliminating lingering water and other possible pollutants.

Any exposed pipe accessible during the test is backfilled, and the property is returned to its original condition.

At public access locations along the testing area, signs are erected to keep people at least 100 feet away from the pipe during the test.

If a pipe breaks during the test, the pressured testing water may spray into the air for a brief while before pooling on the ground. Don’t get too close to the release. [2]

3 Methods of hydrostatic testing

3.1 Water Jacket Testing

A water jacket test is commonly used when checking smaller pressure pipes. Before placing the device in a container filled with water, where changes in vessel capacity are monitored, a standardised tube frequently monitors water levels, the naked look at the device to detect faults. Then, the instrument is inflating, generally for 30 seconds or more, for a fixed period, and expansion is determined by the measuring volume of fluid forced into the measuring tube. It can be measured by assessing volume in the measuring tube before pressurisation. A leak will offer a comparable set property. Still, it may be found if the volume in the pressure vessel instrument is kept constant by clamping the intake valve for a certain amount of time before depressurisation, as this pressure will constantly drop if a leak occurs. A permanent set exceeding the stated limit in most situations implies failure. A leak can also indicate failure; however, the leak may be caused by insufficient sealing on the test equipment. If the instrument fails, it will typically be subjected to a condemnation procedure, in which the instrument will be designated as hazardous. [3]

On the cylinder is printed all of the information needed to define the exam. The design specification, unique identification, manufacturer, and manufacturing date are all included. After successful testing, the date and the test facility’s distinctive mark are generally imprinted on the vessel or its nameplate. A basic test, sometimes called a hydrostatic test, is that the vessel is pressurised by water-filled and leakage physically checked outside. It can be done by anybody using a water tube. This test is suitable for containers not pressurised but which have to function under hydrostatic pressure, such as gasoline tanks. The height above the tank top is usually stated for a hydrostatic test head. Use a temporary tank to fill it with water to the right height if necessary. The tank is pressured. Vents and other outlets may need to be sealed during the test.

Figure 1 Water Jacket

3.2 Proof Pressure Testing

Proof-Pressure testing is a procedure for inspecting the integrity of the pressure shells on new equipment and older pressure equipment and pipes that have been repaired. It is a non-destructive test.

Proof-pressure testing is required for most pipelines to guarantee that a new, modified, or refurbished pipeline can safely carry its rated load while remaining leak-free. Pipes may be required by legal and regulatory authorities, insurance carriers, or the contract terms for the system’s development. Whether or whether proof-pressure testing is legally needed, it serves the important function of safeguarding employees and the general public.

Proof-Pressure testing can also be performed to determine a pressure rating for a component or particular system that cannot be calculated for a safe rating. A prototype of the component or system is subjected to progressively increasing pressure until demonstrable yielding or, in the alternative, rupture occurs. Then, using the necessary derating factors stated in the code or standard for the component or system, a design pressure rating may be calculated from the experimental data.

A Proof-Pressure Test determines if a component can tolerate pressures greater than its designated operating pressure without sustaining irreversible damage. It is a stress test used to demonstrate an Expandable Joint’s fitness under test pressure circumstances.

Unless the hydrostatic pressure test is hazardous or impracticable or cannot safely be filled with water, the proof-pressure test should be a hydrostatic pressure test. A pneumatic pressure test or other tests must be done in these cases.

The proof-pressure test must always be conducted under controlled conditions, with suitable safety measures and equipment, and in such a way that the personnel in charge of the test may check all pressurised sections thoroughly. Test of Proof-Pressure determines if an Expansion Joint can tolerate pressures greater than its intended operating pressure without sustaining irreversible damage. Unless the hydrostatic pressure test is hazardous or impracticable, it is advised. [4]

Figure 2 Proof Pressure Testing machine

3.3 Pressure-Recession Testing

The pressure recession hydrostatic testing method, like the proof pressure method, does not produce a useful measurement of permanent or under-pressure expansion. When a pipe or system is pressurised with water, the pressure source is shut off immediately, and personnel monitors the internal pressure of the pipe while the pressure is applied. This procedure, when combined with a visual examination of the pressured system, aids in the detection of vessel wall thinning and/or deformation.

3.4 Direct-Expansion Testing

Pressurised vessels’ strength and leakage strength such as pipelines, gas cylinders, fuel tanks, and boilers can be measured using a direct expansion test. The test is to fill the pipe system with a liquid. Generally, water, coloured, and pressure are detected for visible leak detection.

It is the test to complete the pipe system with a liquid, typically water, which might be coloured to aid in the discovery of apparent leaks. The test includes the supply of a liquid, generally water, to the system of the vessel or pipe, which can be burnt to aid identify visible leakage and pressurise it at the correct test pressure.

Large containers, such as gas storage tanks, are tested using the direct expansion test method. The amount of water flowing into a cylinder under pressure is measured in this sort of test. When the pressure is released, the amount of water in the expansion measuring device is measured. To get a correct volumetric expansion, the compressibility of water and the cylinder volume under test must be considered.

Large containers, such as gas storage tanks, are tested using the direct expansion test method. The amount of water flowing into a cylinder under pressure is measured in this sort of test. When the pressure is released, the amount of water in the expansion measuring device is measured. To get a correct volumetric expansion, the compressibility of water and the cylinder volume under test must be considered. [5]

4 Traditional vs Digital Hydrostatic Testing:

4.1 Traditional Hydrostatic Testing

Hydrostatic testing utilises pressure decay to measure the integrity of pressure containment vessels such as fabricated pipes, BOP stacks, tanks, well-head, pipelines, reactors, and much more across various industries. A traditional hydrostatic test uses water as the test medium and four main pieces of equipment: a dual-pen chart recorder, deadweight tester, pressure pump, and a pressure gauge. The test requires the operator to record the ambient temperature of the test environment alongside the unit’s pressure under test for a specific period (typically 8 hours) to document any notable pressure leakage not related to temperature fluctuations. In short, the test is designed to find leaks that could compromise the integrity of the vessel while in service. These tests are often performed before the unit goes into service and periodically after the unit is installed (as seen with buried pipelines). Industrial applications include fire suppression systems, newly installed or modified fluid piping systems, leads, tanks, reactors, heat exchangers, air compressors, and distribution systems.

Traditional Hydrostatic Equipment:

1. Pressure Gauge
2. Pressure/ Temperature Recorder
3. Deadweight Tester
4. Hydrostatic Pump
5. Pressure Relief Valve

4.2 Digital Hydrostatic Testing

Digital hydrostatic testing is designed to accomplish the same integrity tests performed with the traditional mechanical setups; however, they require less test equipment to achieve the same result. In a digital hydrostatic test, the operator utilises a digital pressure gauge outfitted with the capabilities to read and record ambient temperature, RTD temperature, and pressure simultaneously. The gauge is placed directly onto the pipe of the system under test or connected with pressure hoses from a safe distance. The operator places the RTDs in their appropriate locations, puts the gauge in log mode, and the test begins. Once the test is completed, the recorded test session is uploaded via custom software to a PC or Tablet for results and reporting. The benefit of a digital hydrostatic test is eliminating the need for large, heavy mechanical equipment. The gauge is twice as accurate as the traditional deadweight tester, which replaces the need to lug it around. The custom software generates a printable pressure/temperature graph showing the test trend, min/max, duration, etc., thus replacing the need for a paper chart. Because the gauge is digital, you can watch the pressure display in real-time with much more precision. Digital reporting also eliminates the possibility that the paper chart gets damaged or lost as all of the raw test data is stored directly in your gauge. Digital hydrostatic test gauges can be used in both hydraulic and pneumatic testing applications. [6]

Digital Hydrostatic Equipment:

1. Digital Hydro Gauge
2. Hydrostatic Pump
3. Pressure Relief Valve

Figure 3 Digital Hydrotsest Guage

5 In-line Inspection

Due to a lack of data, hydrostatic testing is frequently the chosen inspection technique for ageing pipelines. This has prompted concerns regarding inspection tools’ capacity to navigate the pipeline successfully. Along with the hydrostatic test, in-line inspection (ILI) is done. This technique has two significant advantages. First, the ILI is carried out while the hydrostatic test takes advantage of the downtime and water fill. The operational effect and expenses were reduced as a result. Second, doing both an ILI and a hydrostatic test enables the benefits of both inspection methods to be utilised. This increases the capacity to manage risk efficiently in pipelines.

In-line inspection is a preventative maintenance procedure that involves inspecting pipes for corrosion, fractures, and other flaws that might lead to catastrophic breakdown of the system. It’s a type of non-destructive testing. Line inspection is another name for in-line inspection.

The employment of technologically sophisticated tools is required for in-line inspection. A smart pig is one such gadget installed within a pipeline and can travel the whole length of the pipeline. The pig can do contact tests, inspections, and sample collection from inside the pipeline body after installation. It’s also used to keep track of information like wall thickness and dents as it travels down the pipeline. Smart pigs and other in-line inspection devices are critical because they allow the pipeline to remain operational during inspections, avoiding a shutdown or stoppage of product production. [7]

Figure 4 Inline Inspection Pig

6 References

[1] “Overview of Hydrostatic Testing,” [Online]. Available: https://inspectioneering.com/tag/hydrostatic+testing#tabSummary.

[2] B. G. B. P.E., “Hydrostatic Testing,” in Pipeline Planning and Construction Field Manual, 2011.

[3] “BEGINNERS GUIDE TO HYDROSTATIC TESTING IN INDUSTRIAL APPLICATIONS,” [Online]. Available: https://www.precgroup.com/hydrostatic-testing-industrial-applications/.

[4] “Proof-Pressure Test and Leak Detection Test,” [Online]. Available: https://www.macoga.com/documents/en/metal-expansion-joints/proof-pressure-test-leak-detection-test.pdf.

[5] “CGA’s C-1 Publication Reviews Proper Pressure Testing Methods for New and Requalified Compressed Gas Cylinders,” [Online]. Available: https://www.cganet.com/cga-c-1-publication-reviews-pressure-testing-methods-for-new-requalified-compressed-gas-cylinders/.

[6] “DARTT Recorder Portable Hydrostatic Leak & Pressure Testing Equipment,” [Online]. Available: https://www.dartt.com.au/hydrostatic-pressure-testing.

[7] “Overview of In-line Inspection (ILI),” [Online]. Available: https://inspectioneering.com/tag/ili.