Requirement of online hot testing on PSV for boiler 4

[kaoa]

Hi,

Is there regulations or international codes specify to implement periodically the online hot testing on safety valve for boilers to record the blowing pressure? Do the codes mention any provision about personnel safety during this test? Is there any accidents happened before?

(I am aware of Trevi test, but it's not my point)

Thanks for this help.

 

[JAlton]

ASME Sec. I, Power Boilers, Para. 73.4.2, has requirements for Safety Valve Testing. "Trevitest" is one of many lift assist devices accepted by ASME as an alternative to live steam overpressurization on the boiler.

Live steam testing requires raising the pressure in the boiler above the Maximum Allowable Working Pressure of the Boiler while at the same time gagging (rendering inoperable) most of the Safety Valves an the boiler. So, obviously, there is an element of danger in the process. Additionally, the personnel who have to gag and ungag the valves, as well as make adjustments to the valves, are exposed to high pressures and temperatures.

Speaking from experience, I have had my hard hat blown off and my safety glasses imbedded with particles of rust, not to mention burns to my forehead, when a safety valve lifted while I was adjusting it. I have also gotten overheated more than once on a Boiler and suffered from vertigo.

I know a few countries in South America which still require live testing, but most utilities in the USA now use a Lift Assist Device such as Trevitest, EVT, AVK, etc.

Live Steam Testing on the Boiler is the standard for testing against which all other methods are measured, whether Test Bench, restricted lift or lift assist.

JAC

 

[JAlton]

To expand on the subject of Live Steam Testing versus Lift Assist Devices, there was once a big difference between the two methods regarding blowdown or reseat pressure. Until the latest edition of ASME Sec. I, there was a requirement for demonstration of blowdown. Even personnel with the required specialized training often had problems adjusting blowdown. This meant mutiple lifts of the Boiler Safety Valves. In turn, multiple lift increased the chances of damage to the Safety Valve Seating (sealing) surfaces. The lift assist was developed to determine set pressure without fully lifting the safety valve. The lift assist cannot determine full lift or reseat. Recently, however, the ASME Sec. I Committee determined that reseat pressure was not as critical as had been previously thought. Therefore, they removed the requirement for testing/adjusting the blowdown. This makes the lift assist device more acceptable as a comparison to live steam testing than in past years.

JAC

 

[kaoa]

Dear JAC

Thanks for your two valuable replies.

After checking ASME Sec. I, Power Boilers, Para. PG-73.4.2, it seems a requirement for initial installation of safety valve. However, does the code mention the timing and interval of online testing? Should we implement online test every year?

I also found some requirements in ASME Sec. VII, Subsection C4 Appurtenances, C4.130. But I am not sure it was for offline test or online test?

Does ASME PTC 25 specify online safety valve test?

Another question is what differences are among Trevitest, EVT and AVK?

 

[JAlton]

The NBIC is a post construction code which recommends timing and interval of online testing? You should implement online test every year for Sec. I Drum & Superheat Valves unless your jurisdiction will allow longer interval.

The requirements in ASME Sec. VII, Subsection C4 Appurtenances, C4.130 refers to either offline test or online test. Either way is acceptable. SOme Drum & Superheat Valves are welded in line (must be tested in line).

ASME PTC 25 does not specify online safety valve test. PTC onlt specifies how to perform and document testing.

The differences among Trevitest, EVT and AVK are primarily cosmetic. All systems use the same formula and same transducers to calculate set pressure. AVK throws in a random number which makes it impossible to check their calculations (Its purpose is to keep antone from stealing their technology, but they closed that door after the proverbial horse had already left the barn).

There are no major differences in any of the systems. EVT is Dresser and it is leased to their Reps. Trevitest is Furmanite and it is for sale, but very expensive. AVK is also expensive, but they do sell to consumers.

I hope this answers your questions.

JAC

 

[JAlton]

If you need details of NBIC (National Board Inspection Code)

NBIC RB-8410, a. & b.
Boiler under 400 psi, Manual Check (Lift Lever) every six (6) months. Pressure Test annually (On Line, Test Bench, Lift Assist Device) or as determined by operating history.

Over 400 psi, Pressure Test every three (3) years or as determined by operating history.

Test should be conducted prior to bringing the boiler down for scheduled maintenance so that needed reapirs and adjustments can be made while the boiler is down.

JAC

 

[kaoa]

Dear JAC,

Same as your reply, ASME Sec. VII, Subsection C4 Appurtenances, C4.130 also recommend that the testing of safety valves should be performed at the time the boiler is being shut down for inspection. Actually some of our local plants also implemented in this way.

However, I think the purpose of valve online testing is to ensure the valve workable for future continues operation. So the online testing should be done before boiler starting long-term operation, not shutdown. Once a safety valve was dismantled and repaired, it should be tested online with steam again, I suppose.

As for the personnel safety druing testing, can we take the DCS pressure data or trend curve at control room instead of field gauge observation?

Hope to get your expertise soon again.

 

[JAlton]

You are correct about the testing needing to be performed prior to start of long run. The advice in ASME Sec. VII & NBIC RB-8410 are both ideal scenarios which do not give enough details. I started to go into this in my last comment. The best way to properly set, test & adjust a Safety Valve on a large boiler is to make adjustments to set pressure and blowdown as the boiler is coming off line because sometimes testing takes several pops (lifts) to get the adjustments correct. This can cause leakage to the valve from repeated lifting. Then the valve should be dismantled and repaired. During the repair the adjusting ring settings which control the blowdown should be noted and the rings returned to those positions prior to start up. The spring adjusting screw should also be returned to the as found position. Then when the boile ris back up to pressure and temperature is stabilized in the valve (typically 24 hrs running time) the valve should be tested with a Lift Assist Device. This prevents damage from full lifting, but verifies set.

The new ASME Sec. I rules which eliminated the Blowdown Adjustment requirements noe permit a user to simply place the rings per the Original Valve Manufacturer's Specifications. So, Sec. VII should probably be revised to reflect the current procedure in ASME Sec. I.

AS for the pressure reading, most valve testing is done from the control room gauge/pressure transmitter. Not because of safety, but because there is no place to attach a test gauge in many systems. Drums & Superheat Lines especially are too hot to place a gauge in the line without some type syphon below the gauge sensing element.

JAC

 

[GL431]

Does the Trevitest actually render the PSV which is being tested "inoperative" or not? I understand from the below link that the Trevitest device restricts the valve from relieving fully and therefore the valve "has to be declared inoperative" (during the test).

http://www.nrc.gov/reading-rm/doc-collections/event-status/part21/1995/1995066.html

(Page 2 of 4, third paragraph from top, 2nd sentence etc.)

Thanks for your help in advance.

 

[JAlton]

The Trevitest may have a closing ram in order to push the stem down and reseat the valve should it lift and begin to chatter or blowdown extremely long and overheat. However, the closing ram is not typically used, and is often not even installed on the unit due to overhead clearance and other considerations. In any case, as long as the closing ram is not activated the Trevitest does not hinder the PSV from operating.

JAC

 

[WWTraveler]

ASME Sec. I PG-73.4 is a requirement for Manufactures and Assemblers only. It spells out the conditions that allow the Manufacturer to attach the Code "V" stamp. Local Government or Insurer will often dictate the type of testing they will allow. Always check with them before you fully decide which way you are going to test.
I have pressure tested in a lot of countries that do not recognize any of the assist devices. Make sure that the device you will use is accepted in your location.