En 60534-4

[Fortun Bawa]

Whenit comes to control valve testing, experience shows that the level of knowledge how to properly calculate a leak limit is rather low. An explanation for the lack of knowledge could be found in the testing standard EN 60534-4 itself. It simply does not give a profound explanation on the calculation. It only lists a few examples where the leak limit is miraculously created out of few given Information. Those who follow the hint and take a look at the referenced EN 60534-2-1 will find themselves right in the middle of the control valve design calculation jungle. That is the moment when the tester understandably gives up and decided not to deal with it any more. That is why we did write this white paper. It is supposed bring light into the darkness of standards and to take away the horror of threatening mathematics.

As a manufacturer of test benches, both for valve manufacturers and service companies, METRUS GmbH has been familiar with the normative requirements for test procedures for over 40 years. Leakage calculations never played a role until a few years ago. They were simply left to the operators. With the growing popularity of test bench software, however, the expectation grew that leakage could be calculated easily with the software. Today a standard-compliant leakage calculation is part of the software solutions we offer. Consequently, a comprehensive understanding of the interrelationships is mandatory.

Regardless of the test fluid leakage calculation for classes I to IV-S1 is always done in three steps:

1) Check for flow restriction

2) Calculate the rated capacity Q [m/h] according to EN 60534-2-1

3) Multiply the rated capacity Q with the leakage factor as per EN 60534-4

The flow through a pipe or valve essentially depends on the pressure difference between inlet and outlet. The higher the pressure difference, the stronger the resulting flow. However, this correlation cannot be arbitrarily increased. An infinite pressure difference does not lead to an infinite flow.

As already mentioned, test standard EN 60534-4 calculates the permissible leakage as a proportion of the rated capacity. However, since this rated capacity cannot become arbitrarily high, it makes sense to check in the first step whether flow restriction is present.

Describes the expansion factor and is calculated from the previously selected Xsizing and the valves parameter XT from step 1. Within the appendix of this document you will find a table to read Y using Xsizing and XT. The value is in any case smaller than 1. The result of this calculation is the rated capacity of the valve for the test bench scenario. The dimension of the result is m/h.

Leakage class VI, being the highest class for a control valve, stipulates air or gas as the test fluid. There is no calculation for liquids at all. The calculation is based on the seat diameter, the test pressure and a leakage factor listed in EN 60534-4. The result is directly retrieved as a value in ml/min.

In the US and Canada, as well as in all industries related to the oil industry, ANSI FCI-2 is the standard for valve testing. ANSI FCI70-2 and EN 60534-4 calculate the permissible leakage in the exact same way. You can apply the calculation methods shown within this document. There are only two aspects to consider:

For many decades, the bubble counter has been the instrument of choice when it comes to detecting small gas leaks. With the definition of EN 60534-4 sating: 0.15 ml/min = 1 bubble/min, leakage measurement has become possible using simple tools. A glass of water and a tube are sufficient.

If you realise that:

1) EN 60534 calculates permissible leakages as a proportion of the rated capacity,

2) Leakage classes V and VI first calculate a flow rate,

3) The conversion from ml/min to bubbles/min is a help to detect leakages in a simple and economic way

it becomes clear that the approach of counting physical bubbles themselves electronically is not in line with the standard. It appears smarter to detect small leakages with a sensitive flow measuring instrument and to convert them in to bubbles for comparison with traditional glass-of-water bubble counters.

EN 60534 is a set of rules specifically for control valves. Furthermore, there is the industrial valves standard EN 12266 that is mainly used for shut-off valves. Part 1 (EN 12266-1) of this standard contains the requirements for the leakage test.

In general, the following must be observed:

1) The test medium must have room temperature on the outlet side

2) The calculation based on the DN may also be used for diameter-equivalent inch flanges or threads

3) The calculation is based on the nominal diameter (DN) directly, following the table below

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Before getting into the details, let me explain what is generally meant by a tight shutoff valve. When valves are designed and tested, they are engineered to achieve a certain leakage category. The categories are defined and tests occur in accordance with ANSI/FCI 70-2 2006 (European equivalent standard IEC 60534-4). The leakage classes are defined in the following table.

When specifying the leakage class of a valve, if the term tight-shutoff is used, that typically implies the need for a leakage class of VI. As is evident from viewing the requirements for this class from the table above, it is very hard to achieve Class VI even from the design phase of a plant, let alone throughout its entire lifecycle. It is a wonder then, that engineers blithely list the requirement for tight shutoff as a functional safety requirement, when it is so difficult to actually achieve and consistently test for and maintain to.

Some of the confusion lies in the fact that other standards and other requirements would establish the need for tight shutoff, but that need is not a functional requirement of the SIF, and thus should not be documented as such. The most common example is fuel gas shutoff valves on fired equipment. For the SIF of high pressure causing the fuel gas valve (or valves) to close, there is frequently a specification of tight shutoff as a functional safety requirement. While tight shutoff should be specified, it is NOT a functional safety requirement. For the SIF under discussion, whether the shutoff is Class VI or Class III, the process will move to a safe state with respect to the hazard that the SIF is intended to protect against. The need for tight shutoff is independent of the action of the SIF. The need for tight shutoff, which is stipulated in standards like NFPA 86 for boilers, is based on the need to prevent slow leakage of gas into the firebox through closed shutoff valves while the fired device is not in service. While this requirement is valid, it is not a functional safety requirement of the SIF, and should not be treated as such. Otherwise, the tightness of shutoff would need to be established at every functional test of the SIF, and failure of the valve to be tightly shutoff would be considered a failure on demand of the SIF.

While the valve specification should indeed include the requirement for tight shutoff, it should be clear that this is not a functional safety requirement. I.e., this requirement does not need to be achieved in order for the SIF to achieve a safe state on demand. I would recommend that in the safety requirements specifications section for final elements, two fields are available. They should be:

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