Gasket Compatibility with Astro Pak Specific Chemical Processes

Introduction

Selecting a gasket material for a process system contains many tradeoffs. Strength, price, availability, and chemical compatibility must all be considered before adopting a certain gasket into a system. Chemical resistances for common acids, bases, and solvents used in chemicals processing vary across popular gasket materials. For this reason, many companies associated with chemical processing or chemical distribution have developed categorical compatibility and resistance guides for common materials and chemical combinations. It is often difficult to determine the practical implication of these qualitative ratings and the test parameters used to generate the categorical rating though. Further, little to no compatibility data exists for proprietary chemical blends developed by chemical processing companies. The Technical Services Group at Astro Pak recognizes this gap and has tested some common gasket materials with our typical process chemistries for the exact time and temperatures used in our Field Services Division.

Processes

Two groups of six materials were subject to chemical processing. The gasket materials selected are: ethylene propylene diene monomer (EPDM), nitrile (Buna-N), silicone, polytetrafluoroethylene (PTFE), Tuf-Steel (blend of 316L and PTFE), and Tuf-Flex (blend of EPDM and PTFE). Gaskets were imaged and had their thickness and mass measured before and after each chemical process. Table 1 details sample identification and as-received measurements.

Table 1: AS-received measurements
SAMPLE	Thickness [in]	Mass [g]
EPDM 1	0.203	3.723
Buna-N 1	0.201	3.718
Silicone 1	0.201	3.284
PTFE 1	0.176	5.723
Tuf-Steel 1	0.075	2.412
Tuf-Flex 1	0.199	5.107
EPDM 2	0.198	3.762
Buna-N 2	0.200	3.763
Silicone 2	0.197	3.271
PTFE 2	0.198	6.011
Tuf-Steel 2	0.075	2.373
Tuf-Flex 2	0.196	5.033

The chemical processes done were cleaning in a sodium hydroxide solution, Astro Pak’s proprietary, citric acid based, Ultra Pass® passivation process, and a fluoride-intensified derouging process. The processes were run at the exact time and temperature Astro Pak Field Services uses in both shop and field mobilization work. Both groups of gaskets were immersed in a beaker containing the process chemistry and the beaker was subsequently placed in a water bath set to the process temperature.

Results

Table 2 shows the resulting percent changes in thickness and mass following each chemical process. A negative percentage change is a gain in the measurement value between the original and the subsequent process condition.

Table 2: resultant MEASUREMENTS
SAMPLE	After Cleaning		After Passivation		After Derouging
SAMPLE	Thickness Change	Mass Change	Thickness Change	Mass Change	Thickness Change	Mass Change
EPDM 1	-0.7%	-2.7%	-0.5%	-1.3%	-0.8%	-1.5%
Buna-N 1	0.5%	-1.7%	-0.1%	-0.9%	-1.0%	-1.3%
Silicone 1	1.4%	0.4%	2.1%	0.5%	2.2%	0.6%
PTFE 1	0.1%	0.1%	0.5%	1.7%	0.3%	0.0%
Tuf-Steel 1	1.7%	1.7%	1.6%	0.3%	0.5%	3.5%
Tuf-Flex 1	-0.3%	0.8%	0.7%	0.0%	-0.4%	-0.2%
EPDM 2	-2.0%	-0.3%	-2.8%	0.8%	-2.3%	0.5%
Buna-N 2	0.0%	0.7%	-0.5%	1.5%	-0.1%	1.1%
Silicone 2	-1.1%	-0.5%	-1.4%	-0.5%	0.7%	-0.3%
PTFE 2	0.1%	0.0%	-0.3%	-1.8%	-0.8%	-0.1%
Tuf-Steel 2	1.4%	-1.7%	0.8%	0.3%	1.6%	0.0%
Tuf-Flex 2	-1.6%	-3.3%	-1.3%	0.0%	0.3%	-0.3%

Appendix 1 at the end of this report contains photos of all gaskets tested in the as-received condition and after each chemical process.

Discussion

Although sodium hydroxide and citric acid are reported in the industry as compatible chemicals for all gaskets tested in this study, the exact parameters of those compatibility tests are often unreported, and compatibility cannot be guaranteed for a specific process. Results from immersion in Astro Pak’s specific caustic cleaning, Ultra Pass®, and intensified derouging solutions confirm no compatibility concern exists. No appreciable change to mass nor thickness were found after processing two of each gasket type. The largest mass difference reported was a 3.5% decrease after derouging the group 1 Tuf-Steel gasket. 3.5% corresponds to an actual decrease of only 90mg, a negligible amount. Further, the group 2 Tuf-Steel gasket showed zero weight change after derouging. The other largest percent changes reported were negative, meaning samples gained mass between weighing which would be an outcome of incomplete drying and residual rinse water present on the samples. The largest measured thickness change (2.8% growth of group 1’s EPDM gasket) was a four thousandth inch increase, this increase is not large enough to be considered gasket swelling.

The photos in Appendix 1 show no changes in appearance for the gasket samples during processing. Visual evidence corroborates the point that the thickness and mass gains measured did not contribute to any swelling. Visual, thickness, and mass evidence are accurate and sufficient data to ensure full compatibility for all six gasket materials undergoing Astro Pak’s common cleaning, passivation, and intensified derouging processes. 2000000000000000000

Conclusion

Systems containing any of the six gasket materials included in this study are at no risk for chemical incompatibility with Astro Pak’s caustic cleaning, Ultra Pass®, and fluoride-intensified derouging process. As always, proper gasket sizing and installation must be practiced, even when chemicals introduced pose no corrosion concern at normal operating conditions. Fitting grooves are a potential site for crevice corrosion when either incorrect gasket sizes are used, or the correct gasket is installed incorrectly. Further, replacing existing gaskets after performing any of the three processes included in this study is not necessary. The downtime required to chemically process a system does provide a convenient window for gasket replacement, but the governing criteria on replacement should come from the specific maintenance standard operating procedure of the system. Given correct installation, all six gasket materials studied are adequate options for systems to be cleaned, derouged, and passivated with Astro Pak’s Field Service processes.