Stellite seats for steam relief valve 2

[howkers]

I am having trouble with erosion damage to a relief valve pilot seat from wire drawing in a steam application. The Stellite 6 seat is tapered and gives contact at the top edge. The poppet is of Stellite 12 at slightly shallower angle, about 60 degrees inclusive.

I have been advised that Stellite, although very hard wearing in most valve applications, has a susceptibility to erosion by high velocity steam.

Can anyone confirm this for me. In addition could anyone point me to any authoritative references on this subject/problem.

 

[JAlton]

I have seen the same thing in Target Rock Pilots at BWR Nukes. This is an on going problem and to date there has been no sure fix. We are still attempting to solve. We think a better lap job to form a tighter seal may help. This is a tough one.

J. Alton Cox

http://www.delucatest.com

 

[NGiLuzzu]

A look at the following other posts about Stellite[sup]TM[/sup] may be useful:
- Thread725-23517 for general information;
- Thread330-91894 and Thread408-91895 for galling of (self-mated) Stellite 6;
- Thread924-99307 for machining and tools.

My question: what about Stellite 21?

Bye to all, 'NGL

 

[jsummerfield]

I regard wire drawing related to the valve working or leaking past the seat. The valve may be simmering. Consider a very small parallel valve set a bit lower.


John

 

[thorco1]

What is your operating pressure to Set pressure ratio? And what type of pilot valve are you using?

 

[aaabatteries]

From the question it is difficult to determine your exact problem, as I would associate wire draw and erosion as two different issues. I have worked for a reputable safety valve manufacturer for almost 20 years and I would never supply stellite weld overlay on valve seats for steam service. This is because there is a high chance of wire draw lifting the stellite of the base material and thus you get a leak path. If you are getting erosion accross the valve seat, this would be because there is a leak path there. A leak path could be because you have the set pressure too close to the valve set pressure and you have the valve seats in the simmer position. If you insist on using stellite in steam service I would suggest using stellite cast parts for the seating components, therefore you would not get wire draw.

 

[andyenergy]

Can someone explain what wire draw means?

 

[aaabatteries]

Wire draw basically means that because steam is such a searching service, it will find its way between the base metal and the weld overlay, thus removing the weld overlay from the base metal.

 

[andyenergy]

Thanks aaa

 

[JAlton]

Wire Drawing is indicative of High Pressure Steam Erosion of Pressure Relief Valve Seating Surfaces. Such damage typically takes very little time to occur. However, other fluids, especially fluids containing dissolved solids, may cause severe erosion over a longer period of time. In many cases the appearance may be more like that caused by a River waering away rock, whereas "wire drawing" is very straight and more akin to wire cutting methods used in stone quarries, i.e. perfectly straight lines.

J. Alton Cox

http://www.delucatest.com

 

[Multistagedisk]

The only sure way of eliminating wire drawing is by adressing the core problem. Kinetic energy!Now with pressure relief valves you take a single presure drop accros the valve .the min the valve opens you will see a max pressure drop to atmosphere. In the vena contracta of the valve you will reach a velocity higher than mach 0.3 which is the treshold.This piont of high velocity damages the PRV.
Now to eliminate this problem you need to look at Multistage technology where the pressure is taken in a number of right angle 90 dergee turns. this will keep you below the threshold of 0.3mach or 480kpa velocityhead.But now with that said there is no multistage PRVs on the market.But what you can do is add a vent valve that is connected to your DCS upstream to the PRV valve at a setpiont just below your PRV setpiont.