Corrosion for your viewing pleasure :)

[Tycho]

Here are two pictures of a Gram GV-32 valve formerly used as a hotgas valve on plate freezer (pump circulated, ammonia)

Pipes are stainless (316), valves are not. this installation is 4-6 years old.

major leaks on the freezer side of the valve, so not only did it smell bad when defrosting, lots of air got sucked into the plant during the freezing cycle.

cut out the old valve and welded in a new one, and while pressure testing it, the valve next to it sprung a leak so rinse and repeat.

Needless to say, the whole valve skid will be torn down and replaced "when the ship has time" (read: when it falls apart by itself).

anyways, enjoy:

[Tycho]

Btw, this place should have a "house of horror" where things like this could be collected

[US Iceman]

Hi Tycho,

Excellent pictures...

These help to show the importance of insulation and vapor barriers to limit corrosion.

I'm not too surprised the valves look like this. The constant freeze/thaw cycles of hot gas defrost without sufficient insulation or vapor barriers can contribute to the pictures you posted.

Since the majority of material used in ammonia piping systems is carbon steel, this helps to show the importance of adequate surface preparation like primers, paint, and corrosion allowance in piping design also.

Any area of an ammonia system that is subjected to repeat freeze/thaw cycles is subject to this. It just occurs much faster on hot gas defrost lines.

I would hope that people would see this and be aware of what the cause is. Most of the time someone will see this and say, that's too bad.

[Tycho]

seen it plenty times doesnt matter if it's ammonia or *****, as you said, the freeze/thaw process kills it in no time.

forgot to mention that the insulation was "foam" dont know the english word for it, it's the two component stuff that you spray in as a liquid and it turns into a hard foam.

usually works nice, but the casing was full of holes and has been torn down on other occasions when they needed to change the spindle seals on the valves so it sucked water like a sponge.

and that's another point, why the H do some people build the valveskids so that the guys doing the insulation have to put the valve spindle seals inside the box...

I cant count how many times I have had the welders build the skid so that all the spindle seals will be easily accessible after insulation without digging into it, only to have the machinists come around and say "Build it so that only the spindle is exposed" I try explaining that if they get a leak on a spindle seal we will have to tear down part of the box, thereby exposing the foam, and that it will absorb water like there is no tomorrow after that since the box will never be as new again... but nooooo, they wont listen. *sigh*

But when you come back a year or two later and poke your screw driver through the pipes, you are to blame because you did a bad job in the first place sometimes I want to poke them with my screwdriver

[US Iceman]

sometimes I want to poke them with my screwdriver

I agree. They should be poked!

...but nooooo, they wont listen...

That is the problem.

...so it sucked water like a sponge

That is why I believe the vapor barrier is so important. When the insulation gets wet (and it will, sooner or later), the problem becomes much worse, since the wet insulation is next to the pipe.

I am starting to see more of the valve stations (as we call them here in the States) being installed uninsulated. The valves can be ordered with a zinc primer to protect the valve. However, we still have to repair the welded area to provide the corrosion protection.

I have seen the foam you are talking about. For insulation it is OK, but it does not have a vapor barrier to stop the flow of moisture.

I am seeing a BIG problem with the vapor barriers and the insulation installations. At one place where I used to work, we would have the vessels and piping sandblasted to a white metal finish. Then spray on a two-part epoxy zinc primer. Then spray on a two-part epoxy paint. Very expensive and time consuming... However, the carbon steel was very well protected.

The last weak part is the insulation system. If the system is subject to the freeze/thaw cycle this is the worse situation to deal with.

[Andy]

Hi Tyco/Iceman
seen stainless steel valve stations used, looks well, but you need a special primer if you want to put polystyrene insulation our the pipe.

What about denso tape or denso fill (grease tape and poly insulation ball with grease), stops the moisture getting in around the valves

Kind Regards. Andy

[Tycho]

That is why I believe the vapor barrier is so important. When the insulation gets wet (and it will, sooner or later), the problem becomes much worse, since the wet insulation is next to the pipe.

I am starting to see more of the valve stations (as we call them here in the States) being installed uninsulated. The valves can be ordered with a zinc primer to protect the valve. However, we still have to repair the welded area to provide the corrosion protection.

I have seen the foam you are talking about. For insulation it is OK, but it does not have a vapor barrier to stop the flow of moisture.

I am seeing a BIG problem with the vapor barriers and the insulation installations. At one place where I used to work, we would have the vessels and piping sandblasted to a white metal finish. Then spray on a two-part epoxy zinc primer. Then spray on a two-part epoxy paint. Very expensive and time consuming... However, the carbon steel was very well protected.

The last weak part is the insulation system. If the system is subject to the freeze/thaw cycle this is the worse situation to deal with.

I havent seen a vapor barrier (you mean like a plastic sheet or something?) on any valve station (thats what we call it in Norway too, tho my translation software bagged to differ ) we have ever fitted, however the company we use does a pretty good job be it wood boxes or stainless casings, in this case it was a wood box (or plywood with a plastic coating thingymajigg), but it had been opened so many places to service the valves that it just wasnt tight anymore.

We use Danvalve 99.9% of the time, and they are delivered with a hint of a primer coating, it's so thin that if you sneeze close to a new valve, its gone. When supervising a new build I try to give all the valves, or joints between stainless and carbon a workover with primer (same kinda primer they use on the hull, cant remember the name, think it's "coroless" or something), but as I'm only one man on the job and the fact that the shortest measurable time unit is the time between pressuretesting and insulating, I'm at a loss

un-insulated valvestations? where's the point in that?

Hi Tyco/Iceman
seen stainless steel valve stations used, looks well, but you need a special primer if you want to put polystyrene insulation our the pipe.

What about denso tape or denso fill (grease tape and poly insulation ball with grease), stops the moisture getting in around the valves

Kind Regards. Andy

Not sure what you mean by the denso tape (never heard of it) is it by any chance a tape made from sacking covered in grease?

if it is, I've seen that tape used on jackstone platefreezers, around the hose connections, and have come to the conclusion that the only reason it's there is to keep the seawater inside so as to speed up the corrosion process... oh and to make changing a hose more of a tedious task as you have to rip and tear on the grease covered tape, and getting your hands/gloves covered in grease. from personal experience I have seen hoses not covered in such outlive one "protected"