Rupture tube

For a fired reboiler, a pump-around system is used with an FRC to maintain constant flow. There will be a low flow alarm plus fuel shutoff. There will also be a high flow alarm plus fuel shutoff, since a tube rupture would reflect itself in a high flow. 

Stage 1 may last less than one second to several seconds. It is characterized by a very fast transient and a pressure spike immediately after the tube rupture. After the low-pressure side fills with high-pressure fluid, the transition to stage 2... 

Design considerations should be examined by process design engineers when designing heat exchangers for stage 1 tube rupture transient effects, which includes the following ... 

The design pressure of a heat exchanger and other equipment and piping may be exceeded during a tube rupture of an adjacent exchanger if it operates at a high pressure. 

A vapor poeket on the exchanger s low-pressure side can create a cushion that may greatly diminish the pressure transient s intensity. A transient analysis may not be required if sufficient low-pressure side vapor exists (although tube rupture should still be considered as a viable relief scenario). However, if the low-pressure fluid is liquid from a separator that has a small amount of vapor from flashing across a level control valve, the vapor pocket may collapse after the pressure has exceeded the fluid s bubble point. The bubble point will be at the separator pressure. Transient analysis will prediet a gradually inereasing pressure until the pressure reaches the bubble point. Then, the pressure will increase rapidly. For this ease, a transient analysis should be considered. 

The first guideline is often referred to as the "two-thirds rule." The basis of this rule is that if the low pressure side is designed for two-thirds of the high pressure side design pressure, the exchanger hydrotest pressure will not be exceeded due to a tube rupture. 

API RP-521 reeommends transient analysis for exchangers with wide difference in design pressure (such as cases where the two-thirds rule was not applied) because the pressure in the low pressure side of the exehanger ean spike to a level that exceeds the pressure predicted by a steady state analysis when it is liquid-filled. This pressure spike is due to pressure buildup before the liquid is accelerated out of the low pressure side and/or before the relief device opens fully. API RP-521 recommends that the basis for the tube rupture be a sharp... 

Eluor Daniel has the ability to perform a heat exchanger tube rupture transient analysis consistent with the method referred to in RP-521 ("Model to Predict Transient Consequences of a Heat Exchanger Tube Rupture," by Sumaria et ah). This methodology accounts for effects such as the inertia of the low-pressure liquid, the compressibility of the liquid, the expansion of the exchanger shell or tube chaimels, and the relief valve dynamics. Dynamic simulation can be used to meet the following objectives ... 

Determine the size and location of relief devices required to protect an exchanger from overpressure during a tube rupture. 

Investigate the effect of the pressure surge on adjacent equipment per the 1997 edition of API RP-521. The design pressure of adjacent equipment and piping may be exceeded during a tube rupture. This is of special concern in cooling water networks. Dynamic simulation can assess the impact of a tube rupture on adjacent equipment and identify corrective measures. 

Sumeria, V.H., J.A. Rovnak, I. Heitner, RJ. Herbert, Model to Predict Transient Consequences of a Heat Exchanger Tube Rupture, Proceedings-Refining Department, Vol. 55, American Petroleum Institute, Washington, D.C., 1976, p.63... 

Firebox Overpressure - The firebox of a forced-draft furnace and boiler is designed to withstand the overpressure that can be generated by the fans with dampers in their closed position. This needs to be specially checked when both forced and induced-draft fans are provided to discharge combustion products through heat recovery facilities, since higher than normal fan pressures may be used to overcome pressure drop. In the case of high-pressure process furnaces, a tube rupture could also be the cause of firebox overpressure. 

The shell and tube sides of heat exchangers can be designed to contain the maximum attainable pressure on either side, eliminating reliance on pressure relief to protect the exchanger shell in case of tube rupture. 

Operator failure to depressurize during steam generator tube rupture... 

At 40 MW operation, the core damage frequency is 3.7E-04/y. The proportion of accident classes is LOCA, 50% beam tube rupture, 27% ATWS, 17% LOOP, 4% and other transients, 2 7. Three minutes of forced flow are not required and large LOCAs with break size smaller than 2.8 inches can be mitigated. 

In production facility design, the most common relieving conditions are (1) blocked discharge, (2) gas blowby, (3) regulator failure, (4) fire. (5) thermal, and (6) heat exchanger tube rupture. Relief valve design How rates are commonly determined as follows. 

Tube Rupture. It is common for a heat exhanger to have a high-pressure fluid in the tubes and a lower-pressure rated shell. If there is a break in one of the tubes, the higher pressure fluid will leak to the shell, resulting in overpressure. It is conservative to assume a tube is completely split with choked flow from both sides of the break. 

Gas Blowby or Fire Regulator Failure Tube Rupture Fire... 

Woods, D. D. (1982). "Operator Decision Behavior during the Steam Generator Tube Rupture at the Ginna Nuclear Power Station." Research Report 82-1057-CONRM-R2, Westinghouse Research and Development Centre Pittsburgh, PA. 

---