Why do we think of pressure relief as the only way to control pressure, especially when the pressure excursion occurs upstream from the valuable equipment being protected? Conventional pressure relief means product loss, environmental pollution, CO2 pollution from flare systems, extensive downtime, in addition to relief valve and disc maintenance costs. Fortunately, there is a proven, practical solution.

ASME Section VIII UG 125g anticipates isolation technology, yet there is a reluctance to codify this proven technology. The ASME is an active power that suppresses technology and competition, and has become a political organization governed by subcommittee members representing and protecting old technology, methods and institutions – to the detriment of the user industry.

HOW IT STARTED
To the best of our knowledge, the first commercial method to isolate pressure was developed in the oil field over 45 years ago. It consisted of a held ball suspended out of the flow stream. At a set pressure too high or too low, the ball was pushed from the magnetic attraction or collet grip into the flow stream where it would seat to stop flow.

Problem 1
We became involved in a major pipeline problem to meet DOT code governing gas transmission pressure. DOT 192-621(a) states: "Each pipeline that is connected to a gas source so that the maximum allowable operating pressure could be exceeded as the result of pressure control failure or of some other type of failure must have a pressure relieving or pressure limiting device." The transmission pressure varied by localityand proximity to inhabited areas, the gas wells supplying natural gas had supply pressures to 2,000 psi while to DOT regulated transmission pressure varied from 125 psi to 650 psi. The pressure to the entry of the transmission line, and to the entry of the metering station, required a relief valve and its associated flare system. The cost was $3,500 to $5,000 per well with additional maintenance costs required on a continuous basis. Relief was required if the choke at the gas well should cut out and no longer restrict flow. Without pressure relief, pressure at the meter station would approach wellhead pressure. The company already used our reliable Rupture Pin relief valves and questioned if a valve could be made to shut off at set pressure.

Solution 1
The Model "A" valve was designed and furnished for tests within a week. It met all criteria and became the standard. The set pressure varied from 125 psi to 650 psi. The standard size was 2"; however, as the 2" lines joined others, 4" lines were used with a 4" Model "B" ESV on the 4" lines before 12" lines. The 2" valve had a unique characteristic that would force it to close in case of a downstream line break. Here the valve closes, not by excess pressure, but by the flowing mass impinging on the underside of the piston. There is sufficient force to buckle the pin and rapidly close. The cost of this valve was low which resulted in a savings of $3,000 to $4,500 per well. The design was successful. Over 6,000 of these valves are in operation.

Problem 2
The next challenge was at a plant using high-pressure polymerization to produce ethylene. Periodically, the heat exchanger tubes were cleaned by passing low pressure cleaning fluid through the tubes while the reactor pressure was 6,600 psi. A method was needed that would isolate the pressure if during the cleaning process an opening occured in the tubes that would allow high pressure reactor fluid to enter to the heat exchanger tubes and then the low pressure cleaning fluid system.

Solution 2
Special Model "C" emergency shut down valves were designed and mounted on each end of the heat exchanger system. The high pressure end of each valve faced toward the high pressure reactor. In the untripped condition, flow of cleaning fluid was unimpeded, yet should there be an opening in the heat exchanger tube, high pressure polymer would try to escape through both ESV's set at 150 psi. The valves would sense the increased pressure surge and slam closed when the pressure on the stem area reached 150 psi, thus both valves would instantly close to restrict the reactor pressure to the reactor. We were told that isolation occurred on three occassions which saved serious hazards and product loss. The design was a tremendous success and this method of isolating pressure in heat exchangers is widely used by our customers.

Problem 3
In the oilfield, fluids are transported from metal pipe at the wellhead to plastic pipe for some distance to a central processing or transportation facility. The plastic pipe has a pressure rating of about 120 psi. This rating is usually below the possible upstream delivery pressure from a gas or oil well. The plastic pipe must be protected.

Solution 3
A model "E-A" emergency shutdown valve mounted at the junction of metal to plastic pipe can sense the excess pressure and close before the plastic pipe can be affected. The design was successful and proved to be an effective solution to their problem.

Problem 4
A large 12" Model "B" unit was used on a tall reactor. The ESV set pressure was 1,500 psi. A 12" pipeline was delivering gas at 1,000 psi to a reactor. The initial gas pressure was 3,000 psi. A regulator reduced the pressure to 1,000 psi. The MAOP of the vessel was 1,750 psi. The danger was a regulator failure to the open position. A conventional solution would have required two 12" relief valves and a large flare system costing over $2,000,000.00 plus an additional $20,000.00 a year in maintenance and relief valve testing.

Solution 4
It was decided to use a 12" model "B" Rupture Pin ESV before the 12" line entered the vessel. Thermal relief on the vessel required a single 1" relief valve without the need for a flare system. The design was a great success.

Problem 5
In another application, a customer had its feedstock piped from an adjacent plant. Possession was assumed at the fence line. Periodically, operating pressure of the feedstock was excessive and feedstock had to be vented and flared at the customer's expense.

Solution 5
An 8" Model "B" ESV was installed at the fence to prevent excessive pressure beyond the fence line. The design was successful.


WARNING -----------------------------------------------
Emergency shutdown isolation performs very well with gas systems. However, with most liquid systems, you should not close the valve rapidly. To help resolve this problem, the closing can be slowed by using Buckling Pin models "E-A", "E-B", "F-A" or "F-B". On all of these models, the flow rate to the actuator can be controlled and thus the rate of flow. Pulsation dampeners upstream from the ESV have also been successful.