PSV butt weld inlet #2500 - Nozzle Seat Removal 2

[Adnan.B]

Hello Every One,
we have set of PSV's installed on Steam drum. #2500 type 1762, is there a way we can remove and replace only the nozzle seat instead of cutting off the PSV butt welded flange.

thank you so much.

 

[The Obturator]

Difficult these things. The answer is generally No. The OEM may have a device called a Reseating Machine that bolts onto the body where the bonnet is located. The cutting tool has the nozzle face profile. The machine is usually hand operated and will finish cut a new profile, provided the material on the nozzle has not already had it's limit exceeded with previous maintenance. Then just finish lap and its done. You may be able to hire such a machine.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[Adnan.B]

Please check out the attached picture, there is some safety valves i found scrapped and one of them surprized me with the nozzle seat unscrewed this is what makes me wonder if there is some kind of special tool to remove the nozzle.

 

[Adnan.B]

here is the picture of the safety valve nozzle subject for maintenance. unlike the previous picture of the same exact type the nozzle is still attached.

 

[The Obturator]

Don't confuse the nozzle threading as being used to screw into the body - it may be just the nozzle ring threads on the nozzle. It's possible too that a special was made by the OEM. Also someone could have machined out the weld securing the nozzle and gave up. It's best if you take the serial number to the OEM or their local rep to identify the valve for you. The reseating machine I advised on is featured in the 1700 repair manual which I attach here. Page 28 - note nozzle is referred to as a bush. Hope that was useful.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[Adnan.B]

Thank you so much for the clarification, this was very very helpful

 

[The Obturator]

Some end users have in past simply mounted the body on a lathe chuck, centred up the nozzle and machined from there. Just check the integrity of the weld afterwards like a hydro. In cases where there is not enough metal to properly machine a seat to re-machining dimensions shown in OEM manuals, some 'outfits' have welded a layer or two onto the damaged seat and dressed the seat from there......problem is later when the valve is installed and the steam heat is up, the 2 differing materials from original seat and weld material expand at different rates and the seat gets distorted and then the leaks start and get worse. This why some OEMS don't recommend stellited seats. Just thought I'd drop that in.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[Adnan.B]

a portable lathe machine is available for rectifying the seat, the welding is another challenge indeed since we are not sure about the stellite grade.

 

[The Obturator]

It's might not be stellite but a hardened alloy rather than the usual stainless steel at that pressure. The point was, different materials = different expansions. I would check if you have enough material left if you can machine a proper seat.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***