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Pipeline Safety: Hazards Associated With De-Watering of Pipelines

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Research and Special Programs Administration (RSPA), DOT.


Notice; issuance of advisory bulletin.


On June 21, 2004, the Research and Special Programs Administration's Office of Pipeline Safety (RSPA/OPS) issued Advisory Bulletin ADB-04-01 to owners and operators of gas and hazardous liquid pipelines to consider the hazards associated with pipeline de-watering operations. This advisory bulletin was originally issued jointly with the Department of Labor's Occupational Safety and Health Administration (OSHA) as Safety and Health Information Bulletin SHIB 06-21-2004. Operators are strongly encouraged to follow the recommended work practices and guidelines to reduce the potential for unexpected separation of temporary de-watering pipes.

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Richard Huriaux, (202) 366-4565; or by e-mail, This document can be viewed at the OPS home page at The original advisory bulletin issued by OSHA can be viewed at General information about the RSPA/OPS programs may be obtained by accessing RSPA's home page at

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The OSHA Allentown and Wilkes-Barre Area Offices recently investigated two fatalities that occurred in conjunction with de-watering processes associated with newly constructed gas pipelines. In both cases, the temporary de-watering piping violently separated from its couplings, striking and fatally injuring employees. In one instance, the separated section of pipe was thrown 45 feet from where it had been attached to the temporary de-watering valve. OSHA determined that a major contributing factor to both of the accidents was temporary de-watering pipelines that were not adequately secured to prevent the piping from moving or separating. In one case, the failure occurred at a pipe coupler that was not being used within the safe tolerances established by the manufacturer.

After a pipeline is laid, a hydrostatic test is conducted to ensure its integrity. Hydrostatic testing may also be conducted during the service life of the pipeline to evaluate its operational integrity. The hydrostatic test consists of pumping water into the pipeline, pressuring up the line to specified test pressures, and holding that pressure for a discrete period of time in accordance with applicable regulations and guidelines, including regulations Start Printed Page 58226promulgated by RSPA/OPS. After completion of the hydrostatic test, the pressure is relieved and the water is removed from the pipeline during de-watering procedures.

The de-watering process involves connecting a temporary de-watering line to the main pipeline with mechanical couplers and adequately securing the temporary de-watering line to prevent displacement. A de-watering pig is then forced through the main pipeline using several hundred pounds pressure of compressed air. As the pig is forced through the pipeline with air pressure, the water remaining in the line from hydrostatic testing is pushed out of the main pipeline through the temporary de-watering line.

During the de-watering process, significant and sudden variations in pressure often occur within the main pipeline and temporary de-watering line. These variations can be caused by changes in pig velocity as it passes through bends in the pipeline or changes in pig and water velocity due to changes in pipeline elevation. Compressed air escaping around the pig, which can combine with air already present in the main pipeline at high spots in the pipe, can also create a source for stored energy within the main pipeline. These sudden pressure changes produce surges that are transferred from the main pipeline to the temporary de-watering line. This can result in movement of the temporary de-watering line, as the pressures can easily exceed the working pressures and bending capabilities of the temporary de-watering line couplers. The movement of the de-watering line can result in violent failure of the temporary piping system, particularly when the temporary piping is not properly anchored. This situation can be exacerbated when the temporary pipeline suddenly changes direction, when couplers or pipe sections have worn beyond the specified tolerances established by the manufacturer of the de-watering piping system, or when the entire de-watering manifold is inadequately designed for the stresses that can be imposed while de-watering.

RSPA/OPS recognizes the existence of hazards associated with testing pipelines and requires operators to protect their employees and the public during hydrostatic testing. Section 192.515(a) states that “ * * * each operator shall insure that every reasonable precaution is taken to protect its employees and the general public during the testing.” In addition, § 195.402(c) requires each pipeline operator to prepare and follow procedures for safety during maintenance and normal operation.

Advisory Bulletin (ADB-04-01)

To: Owners and operators of gas and hazardous liquid pipeline systems.

Subject: Hazards associated with de-watering of pipelines.

Purpose: To advise owners and operators of gas and hazardous liquid pipelines to consider hazards associated with pipeline de-watering operations and to follow recommended work practices and guidelines to reduce the potential for unexpected separation of temporary de-watering pipes.

Advisory: Each operator of a gas or hazardous liquid pipeline should take recommended precautions against the unexpected separation of temporary de-watering pipes during de-watering procedures. This advisory bulletin was originally issued jointly with the Department of Labor's Occupational Safety and Health Administration (OSHA) as Safety and Health Information Bulletin SHIB 06-21-2004. The original advisory bulletin issued by OSHA can be viewed at, or the RSPA/OPS Web site at

The following guidelines will help reduce the risk of injury to employees involved in de-watering activities:

  • Study the piping system. During the initial planning stage of a de-watering operation, an engineering analysis of the existing and temporary piping system should be performed to identify the pressure associated with fluids and other forces that could adversely affect the integrity of the pipeline or the stability of the drainage and its components. The operator should design the de-watering system and develop installation techniques based on the expected forces of the particular project. Alternatively, designs and techniques could be developed for a “worst case” scenario that could be applied to all de-watering projects.
  • Anchor the de-watering lines. It is accepted industry practice to adequately anchor or secure de-watering piping to prevent movement and separation of the piping. Operators should establish effective anchoring systems based on expected forces and ensure that the systems are used during de-watering projects.
  • Ensure condition of couplings and parts. All couplings and parts of the de-watering system need to be properly selected for their application. The associated piping which the couplings connect is a significant variable in the entire mechanical piping system. The couplings are manufactured in a controlled environment, and variations in the quality of the couplings should be limited. Operators should ensure that couplings are within manufacturer's tolerances and free of damage that may result in connection failure. A chain is only as strong as its weakest link—in de-watering piping systems, the weakest link frequently is the temporary de-watering pipe connections.
  • Provide adequate employee training. This training should instruct employees on de-watering installation designs and techniques, including proper coupling and anchoring methods. Operators should ensure that employees understand the potential hazards of improperly installed de-watering systems, provide employees a means of determining whether the pipe groove meets manufacturer's tolerances, and the procedures they should implement to protect themselves and others working around them.
  • Proper procedures. Operators should ensure that proper installation and de-watering procedures are followed on the job site.

Operators may refer to recommended practices provided by national consensus standards organizations, such as American Petroleum Institute (API) Recommended Practice for Occupational Safety for Oil and Gas Well Drilling and Servicing Operations (API RP 54-1999, Section 12.4.3); American National Standards Institute (ANSI) Power Piping (ANSI B31.1-1973, Section 121.2); and U.S. Army Corps of Engineers (USACE) Safety and Health Requirements Manual (EM 285-1-1, 1996 Section 20).

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Issued in Washington, DC, on September 23, 2004.

Stacey L. Gerard,

Associate Administrator for Pipeline Safety.

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[FR Doc. 04-21829 Filed 9-28-04; 8:45 am]