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. . . . . . . . Approved by John Seabury
Revised 2/2000
7.1 Policy
7.2 Scope
7.3 Pressure Safety Principles And Requirements For All Systems7.3.1 Maximum Allowable Working Pressure (MAWP) and Maximum Operating Pressure (MOP)
7.3.2 Test Pressure
7.3.3 Pressure Relief Devices
7.3.4 Component Requirements
7.3.5 Brittle Components
7.3.6 Pressure Regulation
7.3.7 Pressure System Design
7.3.8 Pressure System Installation
7.3.9 Pressure Testing and Inspection
7.3.10 Pressure System Use
7.4.1 Low-Pressure Gas System Inspections
7.4.2 Low-Pressure Gas System Documentation
7.4.3 Training Requirements for Low-Pressure Gas Systems
7.5.1 General
7.5.2 Training Requirements for Low-Hazard Pressure Systems
7.6.1 Documentation Requirements for High-Hazard Pressure Systems
7.6.2 Training Requirements for High-Hazard Pressure Systems
7.6.3 Other Requirements
7.8.1 Requirements for Closed Cryogenic Systems
7.8.2 General Requirements for Liquid Nitrogen Handling
7.9.1 Division Directors
7.9.2 EH&S Field Support Department
7.9.3 Engineering Division
7.9.4 Engineering Division Director
7.9.5 Facilities Department
7.9.6 Designated Pressure Engineer
7.9.7 Responsible Designer
7.9.8 Pressure Installer
7.9.9 Responsible User
7.9.10 Employees
7.10.1 Berkeley Lab Course Compressed Gas Safety (EHS-231)
7.10.2 LLNL Course Pressure Safety Orientation/(HS-5030)
7.10.3 LLNL Course Intermediate Pressure Safety (HS-5040)
7.10.4 LLNL Course High Pressure Safety (HS-5050)
7.10.5 LLNL Course Pressure Seminar for Engineers (HS-5060)
7.11 Standards
7.12 Related PUB-3000 Chapter
7.13 References
7.14 Appendices (listed below, but linked to separate documents)
1. General
2. Relief Devices
3. Pipe and Tubing
4. Pressure-System Inspection
5. Safety Markings and Signs
1. General
2. Unfired Pressure Vessels
3. Boilers and Fired Pressure Vessels
4. Design and Construction
Appendix C. Safety Note
Appendix D. Pressure Testing And Inspectiona. Testing of Pressure Vessels
b. Testing of Pressure Systems
c. Leak Testing
d. Repairs
e. Modifications
f. Reinspection and Retesting
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Berkeley Lab makes every effort to assure that no injury or property loss will occur from pressure system failures or collapse of systems under vacuum. Whenever possible, Berkeley Lab designs, builds, tests, maintains, and operates pressure vessels and systems in accordance with applicable codes and standards, including the State of California Unfired Pressure Vessel Safety Orders.
For research pressure vessels and systems, Berkeley Lab follows and/or advances the best current industry practice for assuring personnel safety and protection against environmental releases.
These safety requirements apply to all work at Berkeley Lab involving air, liquids, or gases at, above, or below atmospheric pressure. They also apply to any use of cryogenic liquids, since these liquids pose serious potential for over-pressurization in the case of inadvertent confinement.
Pressure system safety is achieved by careful engineering, assuring structural integrity of the components, regulation of pressures and flow, and provision for pressure relief. In some form these principles must be addressed in every pressure system. Therefore, the following concepts and terminology are basic to any discussion of pressure safety. Note that this information is not intended to provide sufficient guidance to design pressure systems, but only to facilitate implementation of Laboratory policies. General guidance is provided in Appendix A, Guidelines for Responsible Designers, and specific design guidance can be obtained through the Engineering Division.
The pressure on which the design of pressure systems is based is the Maximum Allowable Working Pressure (MAWP). At MAWP, the lowest rated component in a manned, ductile system typically has a design safety factor of at least 4.0. To assure that the MAWP is not exceeded, pressure relief devices must be provided. Pressure relief devices must not be set higher than the MAWP for the system. It is important to note, however, that pressure systems cannot actually be operated at the MAWP because the relief devices will open at that pressure.
The highest pressure at which any pressure system may be operated is the Maximum Operating Pressure (MOP). The MOP should be 10 to 20% below the MAWP to minimize borderline actuation of pressure relief devices. Pressure system design begins with establishment of the desired MOP, since all else follows from this.
Standard components often support an MAWP that is substantially in excess of the MOP for any given system. In such a case, the pressure relief device still should be set at 15 to 20% above the desired MOP. This is recommended because operations with unforeseen pressure excursions in excess of 15 or 20% may be out of control.
All pressure vessel systems must be tested to assure their integrity. Low pressure piping or tubing without vessels may be leak-checked only. Commercial systems that have been tested by the vendor need not be retested. Depending on the contents and system configuration, the responsible designer will specify hydrostatic or pneumatic testing. Test pressures vary from 125% to 200% of the MAWP. (See Appendix D.)
The above pressure relationships are illustrated in Table 1.
Pressure relief devices are required for all systems unless the supply pressure is inherently limited to less than the MAWP of the lowest-rated component. Pressure relief valves and rupture disks must be set at no more than the MAWP. The capacity of the pressure relief device must be calculated for systems containing pressure vessels and systems with potentially reactive contents. For pressure vessels, relief capacity must be sufficient to vent the contents of the vessel without exceeding the MAWP by more than 10% under all conditions. For systems with potentially reactive contents, the pressure relief device must be capable of venting the contents of the vessel without exceeding the MAWP by more than 10% when the contents undergo an exothermic reaction at the fastest possible rate.
Adjustable pressure relief valves may be set only by authorized personnel in the Berkeley Lab Facilities Department Regulator Shop, ext. 7669. Rupture-disk assemblies must be certified by the manufacturer, or pressure tested by rupturing three disks selected at random that have been made from the same sheet. Permanent test records must be kept.
Relief devices used with hazardous (flammable, toxic, oxygen depletion, noise, etc.) gases must be vented to a location that will be safe in the event of a large release of gas. Flammable gases must be vented to prevent accumulation of ignitable gas/air mixtures. Health hazard gases (as defined in Chapter 13) must be vented to a location that will not cause inhalation of an unsafe concentration of gas. Venting to a suitable exhaust system is typically required. Contact EH&S Field Support for specific guidance. Venting to a building’s exterior may be acceptable for flammable gases. Exceptions for small quantities or concentrations of gas may be approved by EH&S.
In use, the activation of a safety relief device is a danger signal, like the blowing of a fuse. The system should not be put back into operation until the cause of the overpressurization has been determined and corrected.
Pressure systems must be constructed of components rated for the intended service. Typically, this means ductile metal tubing and rated pressure fittings that are compatible with the contents of the system. Hoses and flexible tubing may be used, but additional protective measures may be required. See also Chapter 13, Gases.
Nonrated components, such as tygon tubing, surgical rubber tubing, hose barbs, RL fittings, etc., are unreliable for pressure use and may not be used where failure could create a hazard. However, such components may be used with low pressure inert gases, or in fume hoods that could safely vent any leaks or ruptures.
Pressure systems (including vacuum systems) with brittle components will generally be operated behind a barrier that can contain shrapnel from failed components. This includes systems with glass and quartz components. The use of safety glasses with side shields is usually adequate for work around view ports and glass feed-throughs on vacuum systems. Pressure systems with brittle components that must be operated without a barrier must have a safety factor of at least 8, and must be specifically designated for such operation in the Safety Note. The Safety Note is the Engineering Division mechanism for assuring safe design of pressure systems.
Pressure systems must have a reliable means of pressure regulation. All
systems supplied by compressed gas cylinders must be equipped with industry
standard regulators. It is recommended that regulators be inspected, and that
regulator relief devices be set by the Facilities Department Regulator Shop.
Specifically, the use of needle valves and other manual flow controllers without
pressure regulators is prohibited on gas cylinder systems
unless components are rated for full cylinder pressure.
Pressure vessels and systems are to be designed, tested, and installed in accordance with applicable codes.
Research pressure vessels and systems often pose challenges that require a deviation from standard designs (e.g., target vessels with thin film windows that do not provide a safety factor of 4). In such cases, the design must provide equivalent personnel safety through alternate means, and these alternate means must be analyzed and documented in the Safety Note. General guidance for pressure system design is contained in Appendix A, Guidelines for Responsible Designers, and additional guidance for utility systems and other facility pressure systems is contained in Appendix B, Facility Pressure Systems.
Safety Note requirements are illustrated in the flow chart shown in Table 2. A template for Safety Notes is provided in Appendix C.
Excellent technical guidance for pressure system design is found in the DOE Draft Pressure Safety Manual, Contact the Facilities Department for questions about conventional plant systems and the Engineering Division for questions about research pressure vessels or systems.
Pressure systems may only be installed by competent personnel. For personnel who routinely install pressure systems, completion of the LLNL Course Intermediate Pressure Safety (HS-5040) is recommended. Technicians from the Engineering Division and from the Maintenance and Operations section of the Facilities Department are available to assist with installation of pressure systems.
Pressure systems operating at pressures greater than 20 Mpa (3,000 psig) gas or 35 Mpa (5,000 psig) liquid may only be installed by certified Pressure Installers. Contact the Facilities Department Regulator Shop for assistance.
All pressure systems which include pressure vessels require testing, retesting, and inspection in accordance with the requirements of the Safety Note. (Exception: utility systems tested and inspected in accordance with State of California Boiler and Pressure Vessel Safety Orders.) Detailed procedures for pressure testing and inspection are given in Appendix D.
A responsible user must be identified for each pressure system. This responsible user is accountable for the safe use and maintenance of the equipment, and for assuring that all training requirements have been met. Typically, this individual is the principal investigator or researcher who is responsible for the overall effort.
Low-pressure gas systems are pressure systems operating below 1 Mpa gauge (150 psig) and consisting only of regulator, tubing, gauges, valves, and fittings. Low-pressure gas systems represent the lowest hazard category of pressure systems at Berkeley Lab.
Prior to initial operation, all low-pressure gas systems must be inspected by the user. The purpose of this inspection is to verify the suitability of the components, the quality of the installation, and the absence of vessels or components that pose a serious hazard.
Low-pressure gas systems may be covered by a Safety Note or an Activity Hazard Document (AHD), but such documentation is not required unless mandated by the hazards of the contents. See description of documentation below.
The user must complete the Berkeley Lab course Compressed Gas Safety (EHS-231) before using any pressure system utilizing compressed gases.
Low-hazard pressure systems consist of equipment with a low hazard level, involving routine risks that are accepted as such by the general public.
Low-hazard pressure systems include:
To determine stored energy, see Appendix E.
The user must complete the Berkeley Lab course Compressed Gas Safety (EHS-231).
Pressure systems that do not fall into the low-hazard category are high-hazard pressure systems. Specifically, high-hazard pressure systems include:
All high-hazard pressure systems must be covered by an approved Safety Note or by manufacturer’s documentation or certification that represents an equivalent degree of safety. In borderline cases, an engineer shall review the manufacturer’s specification and verify that appropriate safety factors are present.
A Safety Note documents the system’s engineering design and defines its operating parameters, as well as pressure test procedures, to assure the safety of the system. For commercial systems, the vendor’s documentation may be substituted for a Safety Note. Safety Notes or the equivalent vendor’s documentation must be approved by the Engineering Division Director or his or her designated Designated Pressure Engineer. A template Safety Note is provided in Appendix C.
An AHD is required for high-hazard pressure systems when:
AHDs for pressure systems require approval by the Engineering Division Director or his or her designee.
Personnel training requirements for high-hazard pressure systems shall be reviewed and agreed on by the user in conjunction with the EH&S Division pressure safety representative. Prior to use of any high-hazard pressure system, each user must also be trained in the requirements contained in the AHD for the given system and in the operating requirements contained in the Safety Note. Additional training requirements may be specified in the Safety Note.
Requirements for pressure testing, retesting, periodic maintenance of pressure systems, barricades, use limitations, and special procedures may be contained in the Safety Note or AHD for any given system.
Vacuum systems that are back-filled from a pressurized supply must be equipped with a pressure-relief valve to assure that the system will not be subjected to pressures in excess of the MAWP. The MAWP of vacuum systems containing commercial glass view ports is limited to 3 psig, unless a higher MAWP has been determined and documented by the responsible designer in a Safety Note. Pressure testing of new vacuum systems is not generally required.
The most severe hazard of cryogenic systems is the possible confinement of even small amounts of cryogenic liquid. Closed cryogenic systems will quickly become pressure systems when trapped cryogenic fluids warm up and cause pressure build-up. Any system that contains valves or fittings that could possibly separate cryogenic fluid from a direct connection with the atmosphere is a closed system.
In addition to the requirements applying to all pressure Safety Notes, cryogenic systems must have:
Small-scale use of inert cryogenics that are not confined (e.g., the filling of cold traps with liquid nitrogen) poses few hazards and does not require safety documentation. The following rules apply to such use:
Division Directors are responsible for assuring that all pressure systems are designed, assembled, and operated in accordance with the requirements of this chapter.
The EH&S Integrated Health and Safety Group administers and maintains the Laboratory Pressure Safety Program. The EH&S Integrated Health and Safety Group is also responsible for arranging the Laboratory Pressure Safety Training Courses, and for maintaining copies of all AHDs and Safety Notes.
The Engineering Division is responsible for reviewing and approving the design, fabrication, installation, and testing of research pressure systems, including vacuum systems, as required by this chapter.
The Engineering Division is responsible for reviewing and approving pressure-system Activity Hazard Documents (AHDs), which are written to assure that pressure operations are within the design limitations of such systems. This is in addition to the normal review process for AHDs, and it does not cover AHDs required for other reasons.
The Engineering Division Director is responsible for designating qualified engineers as Designated Pressure Engineers to provide guidance on pressure vessel and pressure system design, and to review such designs prepared by vendors and by Laboratory personnel.
The Engineering Division Director or designee is responsible for approving any Safety Notes for pressure systems.
The Facilities Department is responsible for the design, fabrication, installation, and testing of all plant facility pressure equipment, as well as the requisite AHDs.
The Facilities Department is responsible for maintaining a sufficient staff of qualified and certified pressure installers, who are available to all groups at Berkeley Lab.
Designated Pressure Engineers are experienced mechanical design engineers who have specific knowledge pertaining to pressure safety, and have been designated as Designated Pressure Engineers by the Engineering Division Director. Designated Pressure Engineers are responsible for:
The Responsible Designer, a competent mechanical designer and usually a member of the Engineering Division, is responsible for:
Completion of Berkeley Lab course Compressed Gas and Cryogenic Safety (EHS 231) and of the LLNL courses Pressure Safety (HS-5030), High Pressure Safety (HS-5050), and Pressure Seminar for Engineers (HS-5060) is recommended before undertaking the design of a pressure vessel or system. (HS-5030 and HS-5050 are prerequisites for HS-5060.)
Pressure installers are usually technicians or mechanics in the Facilities Department who have completed specialized training, and who have been designated and certified as such by their Department Head. Pressure installers must complete the Berkeley Lab course Compressed Gas Safety (EH&S 231) and the LLNL courses Pressure Safety (HS-5030), Intermediate Pressure Safety (HS-5040), and High Pressure Safety (HS-5050). Pressure installers may be assigned to work for responsible designers directly.
The responsible user is the individual responsible for the safe use and maintenance of pressure equipment, including retesting of pressure systems in accordance with the requirements of the Safety Note or AHD. Usually, this is the principal investigator or researcher who is responsible for the overall work. As a minimum, responsible users must complete the Berkeley Lab course Compressed Gas and Cryogenic Safety (EHS 231).
For work at higher pressures, completion of the LLNL course Intermediate Pressure Safety (HS-5040) is recommended. For work with pressures in excess of 20 MPa (3,000 psig) gas or 35 MPa (5,000 psig) liquid, completion of the LLNL course High Pressure Safety (HS-5050) may be required.
Employees who work with compressed gas systems must complete the Berkeley Lab course Compressed Gas and Cryogenic Safety (EHS 231).
Employees who work with pressure systems over 1 Mpa (150 psig) or with pressure vessel systems at any pressure must review training requirements with the EH&S Division pressure safety representative.
For work at higher pressures, completion of the LLNL course Intermediate Pressure Safety (HS-5040) is recommended. For work with pressures in excess of 20 MPa (3,000 psig) gas or 35 MPa (5,000 psig) liquid, completion of the LLNL course High Pressure Safety (HS-5050) may be required.
Required for all employees using compressed gas systems.
Prerequisite for:
Recommended for responsible users.
Required for:
Recommended (and may be required by a Safety Note) for:
Required for Pressure Installers for systems operating at pressures greater than 20 MPa (3,000 psig) gas or 35 MPa (5,000 psig) liquid.
Recommended (and may be required) for:
Required for Designated Pressure Engineers.
Recommended for responsible designers.
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