1.Introduction

1.1  Pipeline Integrity Management

1.1.1 Threats to Pipeline integrity

1.1.2 Integrity Management Practices

1.2 Hydrostatic Pressure Testing

2. Hydrostatic Testing

2.1 The Hydrostatic Testing Process

2.2.1 Pre-Test Planning

2.2.2 Line Filling

2.2.3 Pressurization and Pressure Reduction

2.2.4 Removal and Disposal of Test Media and Residue

2.2.5 Evaluating and Interpreting Test Outcomes

2.3 Safety

2.3.1 Hazard Assessment

2.3.2 Personnel

2.3.3 Testing

3. Regulations and Standards for Hydrostatic Testing

3.1 Regulations History

3.2 PHMSA and MEGA Rules

3.2.1 Background

3.3 Current Hydrostatic Testing Regulations and Guidelines

3.3.1 When Hydrostatic Testing is Required

3.3.3 Hydrostatic Testing Procedures for Gas Pipelines

3.3.4 Hydrostatic Testing Procedures for Hazardous Liquid Pipelines

3.3.5 Spike Pressure Testing

3.3.5 Documentation and Compliance

4. Conclusion

1.Introduction

Pipeline systems are a cornerstone of the oil and gas industry. They primarily function to transport oil and gas products, and are considered to be more efficient, cost effective, and safer compared to other methods of transportation such as truck or train, particularly across long distances¹. Growth in the oil and gas industry in the United States has increased demand on pipeline systems across the country. Additionally, in recent decades, there has been elevated awareness of safety and infrastructural integrity issues associated with oil and gas pipelines.

Adequate pipeline integrity management practices and testing methods during the construction of new pipelines and reinstatement of older pipelines is essential for maintaining the quality of pipeline infrastructure, maximizing assets, and contributes to the protection of environmental and public health¹. Hydrostatic testing is widely recognized as one of the most effective methods of testing to ensure pipeline integrity. Recent standards and regulations (the Mega Rules) have been set forth that govern the construction, commissioning, and re-commissioning of pipelines as well as integrity management practices, and compliance. These standard guidelines promote a safer future for the oil and gas industry.

Understanding the hydrostatic testing process and requirements related to pipeline testing is an important step for maintaining compliance with PHMSA regulations. Thus, the purpose of this article is to briefly discuss pipeline integrity management, describe the processes associated with hydrostatic testing, and examine the updated rules and regulations for hydrostatic testing oil and gas pipelines.

1.1  Pipeline Integrity Management

Though pipelines are considered to be the safer, more reliable method of oil and gas transportation, they can be subject to degradation and other infrastructural failures¹. However, appropriate integrity management practices implemented from the initial point of pipeline construction and planning eliminates these risks¹. Pipeline integrity management plans are developed to facilitate failure prevention and asset protection, as well as reduce environmental and public health risks and product loss.

1.1.1 Threats to Pipeline integrity

Failure in the infrastructural integrity of pipelines can be caused by many factors. One of the most common causes is manufacturing defects, as well as defects that arise during the welding process for pipe seams and joints. Other damages can occur during maintenance, construction operations in the pipeline’s vicinity, or line relocation activities. Of course, the length of time a pipeline is in service is a major driver in the degradation of pipelines. Corrosion and cracking can occur as a result of exposure to the elements over time, and prolonged exposure to high internal pressures or the hazardous material being transported within them can cause failures over the course of a pipeline’s lifetime¹.

1.1.2 Integrity Management Practices

As stated before, pipeline integrity management aims at preventing infrastructural failures in pipe systems to increase the longevity and reliability of pipelines. This involves keeping up with regulatory demands and recommendations for testing, technologies for integrity assessment, and advances in metallurgy for the design of pipe infrastructure¹. Management strategies should involve creating a set process for identifying segments that may be high consequence areas, consistently performing analyses that use all available information about the pipeline’s integrity and failure consequences, and developing criteria for maintenance activities based on what inspection analysis reveals². Maintaining documentation and records of tests, conditions experienced by a pipeline during its operating life, and any anomalies or defects observed is also important to effectively predict and prepare for any issues that may arise.

1.2 Hydrostatic Pressure Testing

Hydrostatic testing is an integral part of pipeline integrity management practices and is the oldest integrity assessment method developed. Hydrostatic testing plays a critical role in the initial commissioning of pipelines and the re-commissioning of older pipelines by ensuring that the system is free of leaks and has the strength necessary to operate without failure³. The primary goals of these tests are to 1) determine maximum operating pressure, 2) ensure the quality of manufactured materials, and 3) evaluate threats to pipeline integrity to develop effective management plans⁴.

Hydrostatic tests are run by sending test media through the pipe system at a greater pressure than that which the pipeline typically operates⁵. These tests are essentially a pass/fail system – either a leak or defect is identified, or it is not. While this integrity assessment method can be used for any segment of piping, it is particularly useful for those that are not easily accessible, such as those underwater or underground⁵. Additionally, depending on pipeline characteristics, alternative inspection methods (such as ILI using pigging technologies) may not be feasible⁶. For example, if the pipeline diameter is not uniform along the entire section⁷.  For these reasons, operators may choose to use hydrostatic testing techniques even when it is not required by code.

2. Hydrostatic Testing

By definition, hydrostatic testing is the process of pressurizing static-state test fluid to examine the infrastructural integrity of a pipeline and define the pressure capacity of a pipeline. Hydrostatic testing is used to establish the maximum operating pressure (MAOP), expose leaks, and evaluate strength/integrity². Hydrostatic testing is also used to verify pipe strength in the presence of potential defects, corrosion, or cracking. Spike pressure tests are most commonly performed to reassure pipeline integrity when corrosion or cracking is present or suspected⁹.

2.1 The Hydrostatic Testing Process

2.2.1 Pre-Test Planning

Before any testing occurs, extensive planning and documentation needs to take place in order to prevent excess stress on any portion of the pipeline being examined⁷. The biggest aspect to consider is the minimum and maximum pressure ranges for the entire pipeline segment undergoing testing, as this will influence the pressure used in the test. These pressure values also determine the regulatory requirements (pressure, timeframe) for an acceptable test.

The location of valves and other pipeline components must be identified and considered as well, along with pipe diameter, wall thickness, internal design pressure, and pipe grade⁷. Most operation managers develop a pre-test spreadsheet to guide the pre-planning analyses⁷. Pre-test sheets should contain information such as the elevation gradient, pipe yield strength, operating pressure, test pressure, and all general pipe data⁷. Throughout this process, the hydrostatic test plan is developed. All operators and workers on-site should be thoroughly familiar with these pre-determined procedures and prepared to carry them out.

Setup prior to the start of testing involves the equipment, tools, pressure meters, and sometimes pumps to be brought on site if not already present⁷. Pipeline block valves, blinds, and pipeline vents must be set up and installed in whatever manner the pre-determined procedures require⁷. Test fluids additionally need to be acquired, as filling pipelines for a hydrostatic test requires large volumes of water². Often, local water sources may be available to utilize for pressure testing. However, fluid management services can aid in this process, often having the resources to supply the total water quantity necessary and shipping pump or portable pump systems needed to fill the pipeline².

2.2.2 Line Filling

To begin the hydrostatic testing process, the line must first be cleaned and cleared of debris. This can be done by propelling foam pipeline pigs through the line with pressurized water⁴. This initial flow-through and product residue should be pushed into a tank for storage. Prior to pressurization, the pressure relief valve must be taken out of service⁷. This valve generally operates to prevent pipes from over pressurization; thus, having it in operation would inhibit the pressurization process for the hydrostatic test⁷.

A temporary connection to the test water tank should be installed, and it must be on the suction side of the pumps⁷. The lines can then be filled. After this, all valves to storage tanks must be sealed off and blinded. It is often a good idea to install a vent valve at the highest point of the pipeline prior to filling to allow trapped air or vapor that collects in these zones to be released⁷. The test head, high pressure pumps, and instruments such as temperature and pressure gauges should all be assembled at this point.

2.2.3 Pressurization and Pressure Reduction

When the line is filled, test fluid temperatures should be observed until it can be confirmed they have stabilized. This is because temperature can influence pressure within the pipe and cause misleading test results. Once this has been confirmed, the pipeline can be pressurized to the test pressure level that was determined in the planning stage. Compressors generate the pressure which should occur at a constant, stable rate until test pressure is achieved⁸. Once the test pressure has stabilized, it must be maintained throughout the entire duration of the test. However, this procedure may vary depending on the type of test (i.e., spike testing) and if a leak is identified⁴.

If pressures drop during the test, fluid can be injected into the line and observed for any additional changes in pressure. If a leak is identified, the test must be discontinued, and the problematic section repaired. The test must then start over to confirm repairs are sufficient.

2.2.4 Removal and Disposal of Test Media and Residue

Upon the completion of the hydrostatic test, the test medium must be cleared from the pipeline. Before flushing the pipeline, the pressure release system isolation valve must be reinstated, and valves and blinds should be aligned appropriately to allow water to leave the pipeline. Test fluid must be disposed of properly because this water or fluid in the pipeline can contaminate the oil/gas product being transported through the system⁵. Additionally, used test media needs to be handled and disposed of safely to eliminate the chance of environmental damage from test media which may contain iron, chlorine or traces of hazardous liquids⁷.

Removal and disposal of test media can be costly in long pipe segments that are large in diameter⁵. On occasion, test media can be re-purposed for the hydrostatic testing of other lines in the near vicinity Pigging is a widely used method to clean and flush pipelines, while older methods involved sending crude pipeline product at a turbulent rate to push water out to ensure the line is packed solely with product ⁷. if there is access to a suitable holding tank⁷.

2.2.5 Evaluating and Interpreting Test Outcomes

Above-ground pipes are the simplest to examine throughout the duration and completion of hydrostatic tests. This is because the pipe can be visually inspected for leaks or bursts resulting from pressurization⁷. Buried pipelines are more complicated because determining the leak location can be difficult when visual examinations are not possible. Small leaks may be particularly difficult to locate, and it is easy for them to be misdiagnosed as trapped product in the test liquid or air pockets. In these cases, dyes are often used to help the test crew locate a suspected leak. Larger pipe ruptures are simpler to identify. Pressure within the pipe will drop dramatically, and liquid will burst through the ground above that segment of pipe. Over-all, if all pressure fluctuations are found to have an explanation, leak tests are considered to be successful⁹.

To further evaluate test results, posttest calculations should be performed. These calculations need to take into account pressure and temperature, as well as the total volume of test fluid lost or gained to account for fluctuations in pressure and other variables that can influence the interpretation of test results.

2.3 Safety

2.3.1 Hazard Assessment

Prior to hydrostatic testing, hazard assessments must be performed. This includes examining the surrounding environment, visually inspecting the pipeline if it is not underground, and examining all pumps, valves, and other equipment and safety controls that will be involved in testing¹⁰. Additionally, it should be confirmed that there is no fatigue among personnel involved in testing. There also must be adequate signage as well as barricades/protective barriers where necessary to establish a safe zone¹⁰.

Another important part of the hazard assessment process is categorizing the test location. High consequence areas (HCAs) are considered to be locations with 20 inhabited buildings within the potential impact zone¹¹. Moderate consequence areas (MCAs) are defined as zones with at least 5 inhabited buildings¹¹. Testing in HCAs requires constant observation of the entire length of the pipeline segment throughout the duration of the test, and responses to deteriorating test conditions must be mitigated in a more immediate response¹². Additionally, water should be the test medium used to prevent hazard risk presented by other fluid mediums¹².

2.3.2 Personnel

All personnel should have adequate experience and training to reduce any chances of operator error during hydrostatic testing. In addition, all personnel on-site should be fully aware of the test plan risks to safety that may arise during testing¹¹. They also need to be knowledgeable of the impact over pressurization has on valves and other components, as well as the dynamics of the pressurization process⁷. Having a high comfort level with operating their equipment (like opening/closing valves) or performing their task is important in order to ensure they have the judgment to know when to perform an action or call to stop the test⁷. Additionally, those reading pressure and temperature monitors need to be able to identify pressure surges, drops in pressure, and know how to read and document data obtained from these gauges⁷.

2.3.3 Testing

Proper PPE should be worn at all times during the course of hydrostatic testing, and unauthorized personnel should be kept off-site¹⁰. Workers should only approach the pressurized pipeline when required for their assigned duties. Additionally, all workers/operators should have “stop authority” and must use it if at any point equipment is not working in a safe manner¹⁰. This is to maximize the ability to catch issues before hazardous conditions arise. All safety related non-compliant activities must be remediated as soon as they are identified.

The pressure release valves and high-pressure switches that are installed and rectify pressure surges must be operated appropriately and in the correct testing phases⁷. Valves accidentally left open or closed can cause pipe ruptures, and improper activation/inactivation of the pressure relief valve can be just as critical⁷. Additionally, no components or fittings should be tightened while the pipeline is pressurized¹⁰.

3. Regulations and Standards for Hydrostatic Testing

3.1 Regulations History

The first recommendations put forth for the use of pressure tests was in (API) standards issued in 1928⁴.  These documents called for pressure testing during the manufacturing process of line pipe material. In 1942, a voluntary code (B31.1) outlined by the American Standards Association (ASA) recommended pressure tests be performed at the time of pipeline installation, and this was widely adopted through the 1950s and 1960s⁴. It was in the 1970s that the Code of Federal Regulations mandated hydrostatic testing for the commissioning and recommissioning of pipelines⁴. However, critical pipeline failure incidents that occurred through the 1990s and 2000s spurred the development of stronger regulations for all aspects of oil and gas transportation pipelines integrity management, testing requirements, maintenance, and emergency response plans¹².

3.2 PHMSA and MEGA Rules

3.2.1 Background

In response to congressional directives outlined in the 2011 Pipeline Safety, Regulatory Certainty, and Job Creation Act, the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) began a 3-phase process of updating the rules and regulations associated with oil and gas transportation safety¹². These are referred to as the “Mega Rule”. The first rule, finalized in 2019, addressed the integrity management in and maximum operating pressure (MAOP) in high consequence areas¹³. In 2021, the second rule was established and primarily dealt with federal safety requirements for onshore gas gathering pipelines¹³. The final rule was released in 2022 and was mainly a response to public and stakeholder comments on what had been established – while there was pushback, PHMSA is certain the new regulations and standards will result in dramatic increases in public and environmental safety¹³. There is lengthy documentation of discourse between the PHMSA, oil and gas companies, and other stakeholders where concerns and recommendations were heard out and solutions reached to establish the MEGA rules and put the final rule into effect¹².

While the ASME standards served as a baseline for the newly developed regulations, the Mega Rule brought about adaptations to these past regulations and standards. Thorough investigations into pipeline failure incidents revealed that past safety measures and pipeline testing were not effective in preventing these occurrences, and that older pipelines constructed prior to the 1970s that had not previously been pressure tested were a primary culprit. Further, the PHMSA found that in many cases, such as that of PG&E in San Bruno, CA in 2010, integrity management strategies built off lacking documentation were arbitrary¹². Proper documentation (operating condition, repairs, and pressure testing history) was not available to examine the history of the failed pipelines.

Presently, the PHMSA hydrostatic testing regulations pertaining to oil and gas transportation pipelines can be found in 49 Code of Federal Regulations (CFR) 195, subpart E, and 49 CFR 192, Subpart J, respectively¹⁴.

3.3 Current Hydrostatic Testing Regulations and Guidelines

3.3.1 When Hydrostatic Testing is Required

The MEGA rules require all piping to undergo pressure tests before initial commissioning, recommissioning, or when any major relocations or replacements have occurred. The rules also emphasize that pressure vessels installed after the rule’s effective date to undergo hydrostatic pressure testing post-installation^15,16. In the event a pipeline operator wants to raise the maximum operating pressure of a previously established pipeline, pressure testing must once again occur to validate the newly desired maximum operating pressure¹⁴.

All untested pipelines from before 1970 must undergo hydrostatic testing. Even if a pipeline has been hydrostatically tested in the past, pressure testing is required if there is not sufficient documentation to confirm pressure testing took place or that MAOP was appropriately established¹². PHMSA does, however, recognize the validity of pressure tests before the 1970s but there must be proof of the previous test’s existence and validity (appropriate test pressure, duration, results interpretation)¹².

Along with this, electric resistance piping and lapwelded pipe from before 1970 should be assumed susceptible to seam failures and undergo hydrostatic testing unless an operator can prove its integrity through documentation or engineering analysis¹⁵. Otherwise, re-testing is required.

Spike hydrostatic pressure tests are no longer required for re-confirmation of pipelines but are still a necessity for threat management¹². This test method is mandated for crack remediation and integrity assessment for cracks/crack-like defects¹². These spike hydrostatic pressure tests must be performed with water to reduce hazards and safety concerns associated with ruptures.

3.3.3 Hydrostatic Testing Procedures for Gas Pipelines

Steel pipelines that operate at a stress level of 30% or more must undergo strength tests to confirm MAOP¹⁶. If these segments are located near areas of human occupancy, pressure must be ~125% of MAOP for at least 8 hours¹⁶. Pre-installation strength test are found acceptable for very short segments of pipe and other fabricated units¹⁶. These tests must maintain pressure at or above the test pressure for a minimum of 4 hours¹⁶.

For gas pipelines, leak tests at no less than the operating pressure must occur when non-welded joints are put in place¹⁶. Additionally, strength tests must be performed when there are piping replacements, but tests when components other than pipe segments are replaced are not required if they have been appropriately tested and passed quality control during manufacturing¹⁶.

3.3.4 Hydrostatic Testing Procedures for Hazardous Liquid Pipelines

For hazardous liquid pipelines, all steel pipelines that operate at or above 30% stress level must undergo pressure testing¹⁵. Test pressures must be at least 125% MAOP and held for 4 hours¹⁵. If the pipeline is not actively being examined for leaks throughout the duration of the test, 4 more hours are required at a pressure of a minimum of 110% MAOP¹⁵.

All piping, fittings, and components must be hydrostatically tested¹⁵. Exceptions to this can be made for smaller components that have been hydrostatically tested at the time of manufacturing¹⁵. Water is generally the required test medium for the hydrostatic testing of oil pipelines¹⁵. In some cases where pipelines are far enough away from populated areas and the test is kept under careful surveillance, liquid petroleum may be allowed as a test medium¹⁵.

3.3.5 Spike Pressure Testing

When spike pressure testing is required, water must be used as the test medium¹⁶. The baseline pressure for the test is determined by material properties and location of the pipeline, but is typically no less than 1.5 MAOP¹⁶. The test must apply pressure at or above the baseline for 8 hours¹⁶. Within the first 2 hours after pressure stabilizes, pressure must be spiked to 1.5 times the MAOP and held for 15 minutes after spike pressure stabilizes¹⁶.

3.3.5 Documentation and Compliance

For both oil and gas pipeline systems, maintaining documents establishing compliance with the MEGA rules is a requirement. Traceable, verifiable evidence of hydrostatic pressure testing, the procedures and results from these tests, and other data related to the integrity, health, and operating conditions (such as exceedance of MAOP) must be retained throughout the entire lifespan of a pipeline^15,16. These records must contain all information needed to demonstrate effective pressure testing at the correct pressure and time intervals and confirm MAOP^15,16. If leak or strength tests have occurred throughout a pipeline’s lifetime, detailed test procedures and the results of these test should be thoroughly documented as well¹². It is the pipeline managers and operators’ responsibility to read, understand, and comply with the new standards set in place¹¹. Integrity management plans should be designed (or redesigned) to meet the PHMSA’s standards and regular reporting is necessary to substantiate operators’ compliance. 

4. Conclusion

Oil and gas pipelines play a critical role in meeting energy demands in the US. In order to continue operating efficiently and safely without causing environmental harm and risking the public’s health and safety, maintaining the integrity of pipelines is of the utmost importance. Hydrostatic testing is an integral part of confirming a pipeline’s structural integrity. Pressure testing at the time of installation, before re-commissioning, and after relocations or replacements ensures the absence of leaks and confirms the line has suitable strength to maintain operating pressures. The new requirements in the MEGA Rules are effective in enhancing the safety of oil and gas transportation, and compliance with these rules will continue to facilitate safety and profitability in the oil and gas industry.  

5. References

1. Kishawy, H. A., & Gabbar, H. A. (2010). Review of pipeline integrity management practices. International Journal of Pressure Vessels and Piping, 87(7), 373-380.
2. Liu, H. (2003). Pipeline engineering. CRC Press.
3. Johnson, J., & Nannay, S. (2014, September). The Role, Limitations, and Value of Hydrotesting vs In-Line Inspection in Pipeline Integrity Management. In International Pipeline Conference (Vol. 46131, p. V004T13A010). American Society of Mechanical Engineers.
4. Hilger, M. M., Mittelstadt, B. C., Piazza, M., & Vieth, P. H. (2016, September). Pipeline Operator Perspective in Use of Hydrostatic Testing as an Integrity Management Tool. In International Pipeline Conference (Vol. 50251, p. V001T03A018). American Society of Mechanical Engineers.
5. Edwards, M. (2014, September). Pipeline Hydrostatic Pressure Test Pass/Fail Criteria Used by a Regulatory Agency. In International Pipeline Conference (Vol. 46131, p. V004T13A001). American Society of Mechanical Engineers.
6. Herckis, C. Understanding the Basics of Hydrostatic Testing of Gas and Oil Pipelines for Quality Control and Integrity Definition. In Pipelines 2021 (pp. 144-153).
7. Bubar, B. G. (1978) Hydrostatic Testing. In E. S. Menon. Pipeline planning and construction field manual. (pp 379-404). Gulf Professional Publishing.
8. Abdulshaheed, A., Mustapha, F., & Ghavamian, A. (2017). A pressure-based method for monitoring leaks in a pipe distribution system: A Review. Renewable and Sustainable Energy Reviews, 69, 902-911.
9. Khan, F., Yarveisy, R., & Abbassi, R. (2021). Risk-based pipeline integrity management: A road map for the resilient pipelines. Journal of Pipeline Science and Engineering, 1(1), 74-87.
10. Construction Safety Consensus Guidelines. (2012). Pressure Testing (Hydrostatic/Pneumatic) Safety Guidelines. CS-S-9. http://www.meridianeng.com/Pressure%20testing.pdf 
11. The PHMSA Mega Rule in practice. how does it impact the industry? Dynamic Risk. (2022, June 9). Retrieved April 19, 2023, from https://dynamicrisk.net/2020/11/14/phmsa-mega-rule-in-practice/ 
12. Pipeline and Hazardous Materials Safety Administration, DOT. (2021). Pipeline Safety: Gas Pipeline Regulatory Reform. 86 FR 2210.
13. Mega Rule Part III: PHMSA Expands Its Regulations and Imposes New Requirements for Onshore Gas Gathering Lines, V&E Energy Update (Nov. 22, 2021)
14. Herckis, C. Understanding the Basics of Hydrostatic Testing of Gas and Oil Pipelines for Quality Control and Integrity Definition. In Pipelines 2021 (pp. 144-153).
15. Combined Federal Register (CFR). PART 195–Transportation of Hazardous Liquids by Pipeline, Washington, DC
16. Combined Federal Register (CFR). PART 192–Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards Revision 03, Washington, DC.