CDTP for Fulflo valve

[Nasim12345]

Dear Sir
I need your advice to calculate the CDTP(Cold Differential Test Pressure) for the Fulflo valve. Pls refer the attached data sheet.

Set pressure is 7.03 Kg/cm2D (differential pressure)
Constant superimposed back pressure is 18.47 Kg/cm2g
Can you pls advice the CDTP? Is it 7.03 Kg/mc2g?

Cold Differential Test Pressure (CDTP)
The cold differential set or test pressure is the actual pressure at which the valve will open on a test stand. As PZVs are usually set and tested at ambient temperature with no backpressure, the CDTP includes any necessary correction for the actual application, based upon backpressure and / or temperature. Backpressure correction is only needed for Conventional PZVs and it addresses constant backpressure only.
CDTP (Conventional PZV) = (Set Pressure – Constant Superimposed Back Pressure) * Temperature Correction Factor.
CDTP (Bellows or Pilot PZV) = Set Pressure * Temperature Correction Factor.
The Pressure adjustment for temperature is specific to the Manufacturer and PZV Model. Consult the manufacturer for discharge temperatures above 150°F.





Thanks
Nasim

 

[The Obturator]

It does not appear that CDTP is represented on the data sheet.

With this being a conventional PRV CDTP should be Set Pressure - Constant Back Pressure + any Temperature Correction Factor

I think that CDTP has been used for set pressure. The data sheet should state both. Set pressure would be 25.5 but this value is stated as the operating pressure.

Give it back to the vendor to correct.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Sabeau]

I also questioned the valve type, conventional piston pressure limiting valve?

 

[The Obturator]

Note also. The subject Fulflo valves are Hydraulic Bypass Relief Valves and not of the API-520/-526 Pressure Relief Valve variety. A PRV data sheet has been used.

Fulflo's technical on-line literature acknowledges that back pressure affects set pressure. You also have a non standard CL. 300 outlet flange due to high back pressure. You best check your question with the vendor.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Sabeau]

That's what caught my attention too, along with the API 614 references.

 

[Nasim12345]

Thanks for your feedback.

Yes, it is a conventional piston type pressure limiting valve. Set pressure is mentioned as [highlight #FCE94F]differential pressure[/highlight]. i.e, 7.03 [highlight #FCE94F]Kg/cm2D.[/highlight] Constant back pressure is 18.47 Kg/cm2g. Presently the valve set in the RV shop test stand is 7.03 kg/cm2g. Our concern is, we would like to know, whether the CDTP value is correct or not? As mentioned by " The Obturator" , I think, set pressure should be mentioned as 25.5 Kg/cm2g instead of 7.03 kg/cm2g.[highlight #EF2929][/highlight]

 

[gguliye]

Dear Sir/Madam,
as mentioned previously:
CDTP is the pressure which the valve is opening on the test bench
it needs to include the back pressure and temperature correction factors
API 520 part 1 says that the CDTP temperature correction is required when the relieving temperature exceeds 250 F however, my practice with Crosby has showed that when the OPERATING NOT RELIEVING temperature is > 150 F, the correction factor is required, u may find it in Installation manual of the relevant manufacturer i think
regarding the valve:
1) determine the type of valve (conventional) or balanced and determine the temperature correction factory
2) if the back pressure is constant, subtract it from the set pressure and multiply the resultant answer with the temperature correction factor (SP-BP)* TEMPERATURE CORRECTION FACTOR
3) If the valve is balanced, u have to only consider the temperature correction factors in the case of CROSBY. Not sure about the manufacturer u mentioned
regards,

 

[gguliye]

Dear Sir/Madam
regarding the pilot valve:
for Anderson greenwood 400 series, piston type modulating valve, i couldn't find any correction factory in the datasheet also checked with the software by increasing the both relieving and operating temperature to 250 F seems no correction is required , however, api says that u have to consult with the manufacturer

 

[Nasim12345]

Dear,
Find below feedback from Fulflo engineering department

“The Fulflo valves operate on differential pressures but temperature normally doesn’t affect the set pressure at which the valve will open as the valve set pressure and then relieves.”

My concern is how to calculate the CDTP. We have more than 7500 PSVs in our plant. But only these two PSVs having concern, how to calculate the CDTP. In all other PSVs data sheet, set pressure is mentioned in kg/cm2g engineering unit, but in these two pzvs, set pressure is kg/cm2D (Differential pressure).

Based on the formula, if we calculate the CDTP, we will get minus value( 7.03 kg/cm2D - 18.47kg/cm2g)...!!!

At present, we have mentioned the CDTP as 7.03 kg/cm2g. As we considered as Set pressure is 25.5 kg/cm2g & constant back pressure is 18.47 kg/cm2g. As mentioned above by " The Obturator" , set pressure should be mentioned as 25.5 Kg/cm2g instead of 7.03 kg/cm2g.

Thanks
Nasim

 

[The Obturator]

Truflo have basically informed you that temperature does not affect the setting.

As advised earlier, this is not a PRV. It is a Hydraulic Bypass Relief Valve.

It is wrongly represented on a PRV data sheet.

I would be taking the CDTP as 25.5 - 18.47 = 7.03

Truflo's own literature states that for differential pressure.

Get your vendor to confirm this and to issue a data sheet representing this.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[The Obturator]

gg Your comment re API-520 advising on temperature correction require above 250'F - Where do you find this?

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Nasim12345]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1574158173/tips/Temperature_Compensation_Chart_xblpxh.pdf[/url]

Dears

Find attached different PZV manufacturer temperature compensation chart.

 

[The Obturator]

Thats a manufacturer chart not API-520. My earlier point is that API-520 does not give a lower/start limit as suggested (in may have done in an earlier API-520 revision), but to obtain from manufacturer. In the case of FulFlo they have answered that they do not compensate.

Regarding also your attached manufacturers chart. It is incomplete. For example, for Crosby, that is the chart for J series (JOS-E/JBS-E). For steam and other valve types the compensation chart is different. The chart also fails to advise that the compensation factor applies to operating temperatured (too many users have taken relief temperature - note Tai incorrectly state this - see API-520).

Finally, chart refers to API-520 6th Edition 1993. we are now on 9TH EDITION 2014 !!!!! Suggest you check your specification data base.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Sabeau]

There have been some substantial changes to the relevant specifications in the last 20 years, I do notice a lot of people seem to be using services like Scribd for access to old documents which exacerbates this problem.

The temperature compensation factor should be outlined in the manufacturers IOM, The Obturator correctly points out that this should be based on operating not relieving temperature as the impact of the thermal effect will not be observed unless the spring is normally exposed to the high temperature.

 

[Nasim12345]

I am having API-520 9th edition 2014(find attached screen shot). Regarding the temperature correction factor, we are still using the updated chart from the respective pzv manufacturer. Yes, i agree that the correction factor chart is incomplete, i just copied & send to you for the easy reference only. WE are having every pzv manufacture updated IOM.

Find attached 2nd screen shot for the discussion with Crosby (Emerson) team in Sept 2019. Just i want to inform you that we are aware about the latest edition of API 520.

 

[The Obturator]

Can you resend the Crosby message in a larger view form - it's too small to read and can't be magnified.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Nasim12345]

See below message

From: Ahmed, Naseer [AUTOSOL/PRM/DHAH]
Sent: Tuesday, September 10, 2019 2:14 PM
To: Kunju, Nasim A.
Subject: FW: CDTP clarification

Dear Sir,

The CDTP was revised after the API 520 9th edition. Please note the below

The last revision of API Standard 520, Part I, Ninth Edition (4.2.3 Cold Differential Test Pressure) provides clarity to the possible ambiguity regarding “service conditions” definition as follows:
“4.2.3.3 The temperature used for the correction factor should be based on the temperature at the inlet to the relief valve at its normal service (nonrelieving) conditions

The temperature correction factors published in technical documents such as Installation, Operation & Maintenance manuals, Functional Test procedures
and also used in sizing software programs (ie: PRV2SIZE, etc.) are based on operating temperature at the valve normal service (nonrelieving) conditions.

Best Regards,

K. Naseer Ahmed
From: Kunju, Nasim A.
Sent: Tuesday, September 10, 2019 11:52 AM
To: Ahmed, Naseer [AUTOSOL/PRM/DHAH]
Subject: [EXTERNAL] RE: CDTP clarification

Dear Naseer

In Crosby PZVs relieving temperature will be consider as operating temperature. In below case operating temperature is below 65 Degree C.

 

[The Obturator]

Thanks. I am unsure what the following comment means. It is contradictory to the earlier statement.

"In Crosby PZVs relieving temperature will be consider as operating temperature. In below case operating temperature is below 65 Degree C"

Only OPERATING TEMPERATURE should be used for CDTP.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Nasim12345]

As per previous Saudi Aramco pzv procedure, for Crosby PZVs, relieving temperature will be considered as operating temperature, while calculating the temperature compensation. May be you have noticed the highlighted portion from the procedure screen shot. Based on API update, it was updated. Now for any manufacturer pzvs, operating temperature will be considered for CDTP.

Thanks
Nasim

 

[The Obturator]

OK Good. It was not clear that the extract was from a SA procedure. Glad that this is now understood and implemented.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.