Testing Gasket Leakage Performance ROTT - ROOM TEMPERATURE OPERATIONAL TIGHTNESS TEST Purpose The ROTT is designed to provide these new gasket constants by monitoring leakage over a series of applied stresses. The first part of the test is a sequence of increasing compressive stress levels where leakage is measured at 400 and 800 PSI internal pressure in order to determine the minimum seating stress. This data is meant to supersede “Y” values. The second part of the test is a series of unload, reload sequences at higher gasket stress levels while 800 PSI internal pressure is maintained. This data is meant to supersede the M value by determining the minimum operating gasket load. This test provides the gasket constants Gb, a, and Gs.

Conclusion ROTT testing demonstrates that ElastaGraph is the tightest seal available through 50,000 PSI bolt-stress levels. This level of stress accommodates virtually every bolting load being used in industrial applications. While it may be possible to provide a theoretic tighter seal at extremely high bolt loads, in practice, bolt load (gasket stress) will drop from this high initial load during operation. Any applications that use more than 50,000 PSI stress will at some point cycle under this load. Therefore, a gasket with a theoretic tight seal at extremely high bolt stresses but a high “Gs” will in practice not be as tight because as the gasket load decreases leakage increases. Therefore, because ElastaGraph is virtually unaffected by changing loads and stress levels (low Gs) and is so tight through virtually every initial load, ElastaGraph proves to be the best possible design available.

HORT - HOT RELAXATION TIGHTNESS TEST 650°F Thermal Cycle Test Purpose The effect of relaxation of bolted flanged joints due to gasket creep at elevated temperature is of importance in terms of tightness loss. The hot relaxation resistance behavior of a gasket material can be examined by performing special hot relaxation tests on the TTRL Universal Gasket Rig which can simulate the rigidity of the specified pipe or heat exchanger joint.

Two procedures have been developed to investigate this behavior depending on the application under consideration. The first procedure is specific to heat exchangers while the second procedure is designed for the pipe flanges. Both procedures may include bolt-load loss recovery after each thermal cycle. This retightening of the bolts known as “hot torquing” is conducted on some heat-exchanger applications, and may also be the case for some standard pipe flange joints for which a slightly modified procedure also exists. The purpose of the HORT test is to test the relaxation resistance of a gasket when subjected to temperature cycling and excessive gasket stress that may be produced during the fluctuating conditions such as those produced at start-ups and shut-downs. There is no acceptance criterion of a HORT test since the resistance capacity of a gasket to creep-relaxation depends on the type of gasket and the application under consideration. The test procedure involves initial compression at room temperature (simulation of bolt-up), three thermal cycles (1 each day) in Helium under creep-relaxation conditions.

Conclusion The Leader GT ElastaGraph™ 1/16'' thick gasket behaved well during the complete HORT test. The short term creep/relaxation resistance of the gasket is good. A maximum stress relaxation of 6.3% was recorded during the third cycle while only 4% was recorded after the first thermal cycle. The gasket overall tightness performance is good. The lowest recorded tightness at the start of the relaxation phase is 9794. After subjecting the gasket to the first thermal cycle, tightness further improved as no leak could be detected with the UGR leakage measuring system.

EHOT - ELEVATED HOT TIGHTNESS TEST 850°F Aging Test

Purpose Emission performance is characterized at room temperature by the new PVRC gasket constants “Gb”, “a” and “Gs”. These Leakage-based gasket constants are determined from the results of two or more ROTT (Room Temperature Tightness) tests. Together, constants “Gb” and “a” represent the capacity of the gasket to develop tightness upon initial seating. These apply at assembly and are valid for any temperature. Constant “Gs” characterizes tightness sensitivity to operating bolt load reductions produced as a result of pressurization or gasket and bolt creep or thermal disturbances that cause load loss.

The purpose of the EHOT test is to prove that applicability of the room temperature constant, Gs, to a “moderately deteriorated” gasket, defined as the damage equivalent to what would be obtained in about 3 years service ( about 1/3 the maximum service life). Therefore, a ROTT test is performed before and after the gasket is inflicted the equivalent damage. The acceptance criterion of an EHOT test is a simple “yes” or “no” on the validity of the pre-exposure “Gs” relative to “Gs” after the exposure. The focus of this validity is that the post-exposure “Gs” would not substantially alter a bolted joint design based on a pre-exposure “Gs”. In this case, the maximum and minimum tightness after exposure may result in a lower post exposure Gs. In this case, the maximum and minimum tightness Tpmax and Tpmin must not have been deteriorated. Conclusion

The design bolt load based on the new code rules that use the constants “Gb”, “a” and “Gs” actually responds to the log of “Gs”. Although, the value of the “Gs” obtained from the ROTT part of the EHOT test, after exposure is higher than that obtained with the preexposure ROTT, the gasket overall tightness performance has slightly improved. As may be appreciated from the SgTp graph of Fig 5, a small shift to the right was obtained in the post-exposure ROTT as compared to the pre-exposure ROTT. In fact, the maximum and minimum tightness Tpmax and Tpmin have improved and consequently the Leader GT ElastaGraph 4” cl 150 lb 1/8” thick gasket passed the EHOT test. During aging and before subjecting the gasket to any stress and thermal disturbances, the gasket tightness was maintained if not slightly improved from 2488 to 2936 values recorded at the beginning and the end of the undisturbed aging. Also, the gasket low stress tightness was maintained every time it is subjected to stress and thermal disturbances and during the post-exposure ROTT. The lowest value of tightness measured during the entire test was 697 measured at the stress levels S1 during the pre-exposure ROTT.

ROTT PERFORMANCE COMPARISONS

ROTT performance comparison of a minimum amount of load required to create a tight seal at a given design pressure.

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LIMITED WARRANTY: Leader GT warrants that its products are manufactured in accordance with its applicable material specifications and are free from defects in materials and workmanship using Leader GT specifications as a standard. Only products which are installed and used in accordance with applicable Leader GT instructions and specifications are in any way warranted by Leader GT. This warranty is applicable only to claims made in writing and received by Leader GT within 30 days after the defect was discovered or should have been discovered and within one year after the date of shipment of the product by Leader GT. All other claims are waived. If a claim is made, you must allow reasonable investigation of the product you claim is defective and you must supply samples that adequately demonstrate the problem you Claim for testing by Leader GT. LEADER GT MAKES NO OTHER REPRESENTATION OR WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, IN FACT OR IN LAW, INCLUDING WITHOUT LIMITATION, LENGTH OF SERVICE LIFE, MERCHANTABILITY OR THE FITNESS FOR A PARTICULAR PURPOSE, OTHER THAN THE LIMITED WARRANTY SET FORTH ABOVE. THIS LIMITED WARRANTY PROVIDES YOUR EXCLUSIVE REMEDY AS A PURCHASER OF LEADER GT PRODUCTS. THIS LIMITED WARRANTY MAY BE MODIFIED OR AMENDED ONLY BY A WRITTEN INSTRUMENT SIGNED BY A DULY AUTHORIZED REPRESENTATIVE OF LEADER GT. WITHOUT AN EXPRESS WRITTEN AUTHORIZATION FROM LEADER GT, NO RETAILER OR DISTRIBUTOR OF LEADER GT PRODUCTS HAS THE AUTHORITY TO MODIFY OR AMEND THIS LIMITED WARRANTY. The physical or chemical properties of Leader GT products represent typical average values obtained in accordance with accepted test methods and are subject to normal manufacturing variations. They are supplied as a technical service and are subject to change without notice. Check with Leader GT Corporation to assure current information.

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