Frame 5 Gas Leaktest

N

Thread Starter

Nigamhyd

Gas leak test is required for the integrity of the SRV & GCV /Vent valves. So why it is not required for the frame5 GE machine used by oil & Gas?
 
GE Frame 5 fuel gas system is very vital in gas turbine because any fuel gas leakage through these 2 valves mentioned make fuel gas in the combustion chamber and while startup make problem for explosion. hence, always both valves to be leakage shall be ANSI leak age class shall be 4

regards
saradhi

> Gas leak test is required for the integrity of the SRV & GCV /Vent valves.
> So why it is not required for the frame5 GE machine used by oil & Gas?
 
rvsaradhi,

The gas fuel valve leak test was originally implemented because GE Safety Review Board felt it was necessary to protect against lawsuits. I believe it is also now required by some nations and regions and local technical regulations and/or standards. In many cases GE "forced" this test on Customers without telling them about it when they purchased a control system upgrade--whether it was required by local technical regulations and standards. Many times when the Customer became aware of the test--when it prevented starting--GE told them it was "mandatory" <b>without</b> explaining it was required by GE to protect GE against lawsuits.

The original poster did not provide enough information about the facts concerning his query. For example, is he referring to a unit or units which have been operating for some time? Because many times older machines are not required by any technical regulation or standard to implement such testing. Perhaps the original poster worked at another site where the test had been implemented or was provided with a new unit or a new control system upgrade.

While a very valuable test, it has been my painful experience that it was not configured correctly by GE or the commissioning personnel and has caused a LOT of starting problems over the years. Especially for sites that don't know about or understand the intent AND that don't perform adequate maintenance.

So, while those who have knowledge of and experience with the test are "at peace" with it, some just ass-u-me it should be on every GE-design heavy duty gas turbine regardless of age or application. And those same people have usually learned painfully of the existence of the test and just believe every unit should be subjected to the pleasures of protecting GE against lawsuits--whether the local or national technical regulations and standards require the test or not.

So, the correct answer is: Does site or local or national technical regulations and standards require the particular turbine or turbines in question to have the gas fuel valve leak test? If yes, then it should be implemented. If no, then it's not necessary.
 
Another great answer CSA. As you say the leak test seems a great idea but some of the pass/fail parameters set by GE are a bit crazy. For example, on a Frame 6 DLN1 machine, Test #1 was only allowing 1.5 psi leakage across the SRV in 30 seconds, pretty hard to achieve.
 
Hi,

please note that for 2 valves in fuel gas line for frame 5 heavy duty gas turbines when you are going to major overhaul, leakage test is mandatory. oil and gas industry we have 14 GE FRAME 5 machines. we have to do PM jobs for your plant safety.

kindly as test for your machine and well personnel HSE

REAGRDS
saradhi

> Gas leak test is required for the integrity of the SRV & GCV /Vent valves.
> So why it is not required for the frame5 GE machine used by oil & Gas?
 
rvsaradhi,

When one of the 14 GE-design Frame 5 units at your site fails the gas leak test during a start, what happens? What is the procedure for responding to a failed gas leak test?

Do you have a spare combined gas valve assembly and a trained crew at the ready with tools and equipment to swiftly swap the assembly to return the unit to service with a refurbished and tested gas valve assembly? Is the removed assembly quickly refurbished and made ready for substitution?

Do any of the units use independent gas valves? If so, who manufactures the valves--and what is their failure rate per year?

How many gas leak test failures occur in one year at your site?

What are the parameters for the gas leak test at your site? Are all the units using the same parameters?

How many GE-design Frame 5s experienced catastrophic failures due to failed gas valves prior to the implementation of this test? And, of those unit that did experience catastrophic failures how many sites were aware of existing gas valve leaks and failoto take corrective action? How many practiced unsafe starting procedures, violating purge time requirements to get the unit started quicker? How many forced firing attempts without regard for purging requirements because of the need to get the unit started?

I'll venture an educated guess that many sites that did experience catastrophic failures due to leaking gas fuel valves were not following proper procedures for purging and were in fact trying to circumvent safeguards with the knowledge that fuel valves were leaking. There was a post to control.com a few years back where the poster openly asked what could be the cause of loud booms in the exhaust during starting--repeated loud booms. There have been several posts also about forcing the leak test failure logic to get the unit started.

Safety is not something which can be "built in" to a piece of equipment--because there are always people who will bypass safety interlocks trying to cheat luck thinking they know better--when what they're really trying to do is make money, generate revenue and profit by taking risks. Sometimes very poorly thought out risks. And when the OEM does a poor job of configuring parameters for "safe " tests, well they're just inviting people to bypass safety. And when they don't document the test and the intention and the risks then, well, you can guess the results.

But, please tell us about how management responds to failed gas valve leak tests at your site.
 
Hi,

please note that frame 5 machine GE FUEL GAS LINE VALVES has to pass leakage test if these valves does not pass as per standards and replace with brand new valves.

valves more reliable and dependable valves. if valves are passing gas turbine will go into different status/condition. it will affect many more turbine Performance.

regards
saradhi
 
C

Controlquest

What is the safety aspect for Gas Leak test? I saw old machines which run without any gas leak test. Is there a regulation to conduct Gas Leak test as mandatory?
 
Depends on the country and their gas regulations. In many countries the answer is Yes. Remember the SRV is really the Stop/SRV, do you want a safety Stop valve that leaks?
 
> Could you please explain how k86GLTA & K86GLTB was derived?

The answer depends on the version of the gas leak test; there are at least two factory versions and more which have been notified in the field.

There is a formula for each of the two factory versions, but unfortunately they don't take into account the actual speeds which are experienced during starting, instead using TNK14HM1 which is just minimum firing speed level--actual firing speed for many units is several percent above that--which if not taken into account during factory calculations can cause lots of problems during initial commissioning.

The formula adds a upper and lower limit as a percentage of expected fuel pressure vs. speed.

The biggest issues I encounter with this bit of logic are the lack of familiarity and understanding on the part of commissioning personnel who lack the knowledge to properly explain and calculate correct Control Constants, and therefore struggle to explain what and why and cannot justify the test or its usefulness.

When operations personnel are unaware of the test's existence and purpose and experience problems starting they are understandably frustrated and can become quite agitated, even angry. This occurs most frequently on turbines which have been upgraded to a new Control System and were unaware of the test and have older control- and stop valves which leak and have probably done so for a long time--but now suddenly prevent starting. This lack of documentation about this new "requirement" before it causes trips and starting problems is compounded when field service personnel can't explain or quickly resolve the issue--if it's just one of a very tight window of acceptability.

And this is the biggest issue--because the control system supplier chooses the allowable limits of acceptability. When the Control Constants are calculated correctly they limits are chosen based on industry standards for acceptable shut-off and control. But when operations personnel encounter an issue with passing the test there is no documentation which can be referred to to support the supplied limits. Which leads to huge battles about what is or isn't acceptable--and for how long leaks can be tolerated, and how much is an allowable deviation to support operations until maintenance can properly address the issue.

While newer versions of the test annunciate an alarm before tripping, because operators aren't away of the test, the alarm and trip limits, and just generally ignore alarms as long as the unit starts and runs the alarms get overlooked until the test does finally result in a trip--and then all hell breaks loose.

This test is basically to protect owners and operators from damage and injury resulting from a condition which wasn't monitored for decades. It also protects the control system supplier from litigation and damages--which is very important to the control system supplier, too.

But the lack of documentation about the test and how the allowable limits are determined--but most importantly how much deviation can be safely tolerated for how long--makes this test contentious and onerous and questionable. Without proper documentation and awareness and knowledge it causes more frustration and grief than can be imagined.

Which is probably the reason for the urgency of this query in more than one thread (if the whole story were known).
 
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