Tag Archives: ASTM

ASTM International Committee Releases Latest Room Temperature Tightness Test

The American Society for Testing and Materials (ASTM) International Committee F03 on Gaskets recently released the latest standard practice to derive gasket design constants for the proper design of bolted flanged joints (BFJs): ASTM F2836-18. End users of gaskets can then use these gasket constants for proper BFJ design using calculation methods that are currently being developed by a special working group of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section VIII at the time of this publication. In this article, the current test procedure, the mathematical models of the test evaluation and the calculation of the characteristics are described and discussed.

IMAGE 1: Example of a servo-hydraulic test stand (Images courtesy of Amtec North America, Inc.)

Background

Most industry professionals are aware that BFJs used in fluid service are complex mechanical systems. In order to create a high-performing BFJ, a designer needs to carefully consider not only the service conditions the BFJ will encounter, but also the performance characteristics inherent to the components of the BFJ. The gasket itself is one of these critical, yet often overlooked, components, and efforts to determine and quantify the performance characteristics of gaskets have been ongoing for decades.

The newest of these efforts to be published in the United States is ASTM F2836-18: Standard Practice for Gasket Constants for Bolted Joint Design (commonly referred to as the Room Temperature Tightness Test, or ROTT). The design constants produced by this method enable a more robust design of BFJs compared to previous, antiquated design constants, such as the m and y factors.

The crucial gasket constants produced by this standard practice are a, Gb and Gs. These constants effectively describe the tightness behavior of the gasket material, reflective of different loading and service conditions.

In addition to their application to the ASME calculation method currently under development, the constants can also be used to compare materials so the proper one may be selected for the application.

IMAGE 2: High-pressure test sequence

Who Will Use ASTM F2836-18?

ASTM F2836-18 is a helium leakage testing and evaluation method that determines tightness-based design constants at room temperature for pressurized bolted flange connections that are designed in accordance with ASME BPVC. As such, ROTT applies mainly to all types of circular gasket products—including, but not limited to, sheet-type, spiral wound, solid metal and jacketed gaskets.

As such, these constants stand to be of interest to all parties who work with circular gaskets and have a vested interest in producing a high-performing BFJ, including end users, BFJ assembly contractors and gasket manufacturers.

Testing Procedure

The test method consists of analyzing data from multiple gasket leakage tests in order to calculate the three aforementioned design constants for a particular model and size of gasket. The testing can be performed in a pair of appropriately sized flanges, using bolts to achieve varying gasket loads, or in a servo-hydraulic test stand of adequate capacity (Image 1).

In total, the procedure consists of two high-pressure (HP) tests at 6 megapascal (MPa) (870 pounds per square inch [psi]) of helium and two low-pressure (LP) tests at 2 MPa (290 psi) of helium, for a total of four tests on four different specimens. In addition to the differences in internal pressure, the HP and LP tests are also distinct from each other in terms of the gasket loading sequences.

The HP test consists of loading and unloading sequences, continually introducing successively higher loads onto the gasket while interrupting this loading sequence with intermittent unloading ramps. The LP test consists of only a loading sequence.

In both tests, the helium leak rate is measured at these various gasket loads.

For the purposes of test evaluation and gasket constant derivation, the different loading sequences of the tests are categorized as either Part A or Part B. Part A consists of the loading sequences, while Part B consists of the unloading sequences. Therefore, the HP test contains both Part A and Part B sequences, while the LP test consists of Part A only.

IMAGE 3: LP test sequence

See Image 2 and Image 3 for details of the HP and LP testing sequences, respectively.

With its increasing gasket loads, Part A simulates assembly of the gasket in the joint, and therefore represents the gasket seating process. The data from this portion of the test is used to determine the required seating load for the gasket to create a tight seal.

Part B simulates the operating conditions by unloading the specimen to different gasket stress levels. This replicates unloading of the gasket, seen in real applications, due to various factors including internal pressure and relaxation effects of a gasket during operation. Part B test data is used to determine the required operating gasket load in order to maintain a tight seal. Continue reading ASTM International Committee Releases Latest Room Temperature Tightness Test

Is an ASTM Callout the Best Way to Specify Your Elastomer Needs?

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Fred Fisher, Technical Sales Manager for Parker O-Ring & Engineered Seals Division.


ASTM Elastomer Compounds

elastomer materials pictureWhen looking at drawings to define a specific application or elastomer requirement: Is there value in using an ASTM elastomer compound description versus listing an approved Parker compound number?

Specifying a compound using the ASTM callout is a good start – it clearly defines what is wanted and it sets a minimum benchmark, which makes it easy for competitive vendors to understand what the need is. The ASTM standards also set specific test parameters which makes it much more simple to do an “apples to apples” comparison between two compounds. However, over time, here is what customers have learned:

Know Your Operating Requirements

1. The ASTM standards are very general; so when a customer defines a specific FKM they need using an ASTM callout, they might receive a compliant material that just barely meets the ASTM specifications, but did not meet the actual operating requirements. Because of that, a supplier may provide a customer with the lowest cost material. Let’s say the quality of the material is on the lower-end, but it meets the ASTM criteria requested. Because of that, the customer could see a 15% increase in assemblies requiring rework, plus a rising number of warranty claims due to seal failures. The twenty cents per seal that the customer saved for their $50 application would be offset by the cost of the increased product failures. And ultimately, this would result in an unhappy customer.

Know the Fluids Your Seals Will be Exposed to

fluid exposure2.  The ASTM standard does not specifically list what actual chemicals the seal has to be compatible with as well as the operating conditions. ASTM tests compatibility based on Standardized Testing Fluids, which are: Oils, Fuels, and Service Liquids. ASTM uses standard oils, which are defined by IRM 901 and 903. Again, the ASTM standards are excellent for comparing compounds, but most people do not have their seals operating in the ASTM reference oils and many sealing applications are exposed to multiple fluids.

Know What Your ASTM is Calling Out

3.  Most engineers or folks in purchasing who review or utilize older drawings have no idea why the original engineer chose the specific compound or why they used an ASTM callout.

So what is the best way to define and specify an elastomer? Most companies go through a technical process to specify, test. and confirm that an elastomer is the correct choice for their application. All elastomers tested and approved for the application should be clearly listed on the drawing. In addition, the drawing should clearly state that  the approved materials listed were tested to confirm their suitability for the application. All substitutes or new elastomers must be tested and approved by engineering prior to use.


Gallagher Fluid Seals is an authorized distributor for Parker. For more information about their products, including o-rings or their various compounds, contact Gallagher Fluid Seals today.