A quick search of SAFTENG.net and one will see that over the years I have written dozens of articles discussing the need for hydrostatic relief protection on piping where a liquid that gets blocked in could expand and rupture the pipe. Yet it seems that each industry somehow feels the need or requirement does not apply to them. OSHA specifically calls for the use of hydrostats in their Ammonia and LPG standards and the most common piping RAGAGEPs also REQUIRE them…
B31.5 REFRIGERATION PIPING AND HEAT TRANSFER COMPONENTS
501.4.2 Fluid Expansion Effects (Increased Pressure). Consideration must be given to expansion of liquid refrigerant trapped in or between closed valves and a means provided to prevent overpressure.
B31.3 Process Piping
F301.4 Ambient Effects Where fluids can be trapped (e.g., in double seated valves) and subjected to heating and consequent expansion, means of pressure relief should be considered to avoid excessive pressure buildup.
ANSI K61.1 AMERICAN NATIONAL STANDARD SAFETY REQUIREMENTS FOR THE STORAGE AND HANDLING OF ANHYDROUS AMMONIA
5.8.12 A hydrostatic relief valve shall be installed in each section of piping (including hose) in which liquid ammonia can be isolated between shut-off valves to relieve the pressure that could develop from the trapped liquid. The discharge opening from any pressure relief valve shall not terminate inside any building or below the highest roofline of any such building.
API 521 – GUIDE FOR PRESSURE-RELIEVING and DEPRESSURIZING SYSTEMS
3.14 Hydraulic Expansion 3.14.1 CAUSES Hydraulic expansion is the increase in liquid volume caused by an increase in temperature (see Table 3). It can result from several causes, the most common of which are the following: a. Piping or vessels are blocked in while they are filled with cold liquid and are subsequently heated by heat tracing, coils, ambient heat gain, or fire. b. An exchanger is blocked in on the cold side with flow in the hot side. c. Piping or vessels are blocked in while they are filled with liquid at near-ambient temperatures and are heated by direct solar radiation. In certain installations, such as cooling circuits, the processing scheme, equipment arrangements and methods, and operation procedures make feasible the elimination of the hydraulic expansion-relieving device, which might normally be required on the cooler fluid side of a shell-and-tube exchanger.
In certain installations, such as cooling circuits, the processing scheme, equipment arrangements and methods, and operation procedures make feasible the elimination of the hydraulic expansion-relieving device, which might normally be required on the cooler fluid side of a shell-and-tube exchanger. Typical of such conditions would be multiple shell units with at least one cold-fluid block valve of the locked-open design on each shell, and a single-shell unit in a given service where the shell can reasonably be expected to remain in service, except on shutdown. In this instance, closing the cold-fluid block valves on the exchanger unit should be controlled by administrative procedures and possibly the addition of signs stipulating the proper venting and draining procedures when shutting down and blocking in. Such cases are acceptable and do not compromise the safety of personnel or equipment, but the designer is cautioned to review each case carefully before deciding that a relieving device based on hydraulic expansion is not warranted.
ASHRAE 15-2010 – Safety Standard for refrigeration Systems
9.4.3 Hydrostatic expansion. Pressure rise resulting from hydrostatic expansion due to temperature rise of liquid refrigerant trapped in or between closed valves shall be addressed by the following.
9.4.3.1 If trapping of liquid with subsequent hydrostatic expansion can occur automatically during normal operation or during standby, shipping, or power failure, engineering control(s) shall be used that are capable of preventing the pressure from exceeding the design pressure. Acceptable engineering controls include but are not limited to the following:
a.) pressure-relief device to relieve hydrostatic pressure to another part of the system
b.) reseating pressure-relief valve to relieve the hydrostatic pressure to an approved treatment system.
9.4.3.2 If trapping of liquid with subsequent hydrostatic expansion can occur only during maintenance—i.e. when personnel are performing maintenance tasks— either engineering or administrative controls shall be used to relieve or prevent the hydrostatic overpressure.