Corrosion for your viewing pleasure :)

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:

http://www.pbase.com/kimmo98/image/55787495.jpg

http://www.pbase.com/kimmo98/image/55787497.jpg

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

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.

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 :D

Quote:

---

sometimes I want to poke them with my screwdriver

---

I agree. They should be poked!:D

Quote:

---

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

---

That is the problem.:(

Quote:

---

...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.

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:)

Hi Andy,

I know of some people who have used the grease tape. I have heard it is expensive and the insulators do not like it.

It changes the outside diameter of the piping and makes the insulation hard to fit up.

I do not have first hand experience with, so I am going on others comments.

Quote:

---

Originally Posted by US Iceman

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 :D

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

Quote:

---

Originally Posted by 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:)

---

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" :)

Quote:

---

...the shortest measurable time unit is the time between pressure testing and insulating

---

I understand what you mean. Jobs are always hurry, hurry, hurry...

Quote:

---

un-insulated valve stations? where's the point in that?

---

I know it seems backwards, but when you look at the problems with insulated valve stations it is cheaper and I think more effective to leave them uninsulated. The refrigeration contractors have been leaving the valve stations uninsulated for some time.

If the valve station is in a processing room or other inside room we normally install a stainless steel pan under the valve station to catch the water drips.

The trend here in the States is put the piping on the roof. Insulate all of the pipe and fittings and service valves, but not the control valves (regulators, solenoids, strainers, etc). The valves that get worked on all of the time are exposed.

Quote:

---

...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

---

This is similar to what I was saying before. Sometimes it is better to leave it unprotected.

Here is a link to the Dow website. There are several bulletins about installation guidelines. The vapor barrier I mentioned before is called Saran (also from Dow). A couple of the files are close to 2 meg.

http://www.dow.com/styrofoam/na/dowp.../index.htm#pdf

Hi Iceman/Tyco:)
The Dow/Saran solutions looks like a good option. Most insulation to date in Ireland has been Polystyrene. This will be a no no shortly. Every week a food factory burns down in the UK, insurance companys are now wise to Poly fridge panels and will come aware of poly pipe insulation.

Better leave the valve stations un-insulated, that is why I mentioned stainless pipe. RS/Parker will sell you stainless control valves and shut-off valves.

Denso tape is simply greased tape. I wouldn't use it on all the insulation, but I would use it on the ends next valves.Denso fill is good for valve staion boxes, around valves.

I have to say the Dow product looks the part, next job I will look at using it.
Iceman how does it compare price wise to Poly and PIB (rubber sheet).

Kind Regards. Andy.

Quote:

---

Originally Posted by Andy

how does it (Dow Products) compare price wise to Poly and PIB (rubber sheet).

---

Andy, I do not have any prices for comparison. There should be a Dow office in the UK, you might contact for this information though.

I like the stainless steel idea, especially for the areas that go through a freeze/thaw cycle. There are some contractors starting to look at using 304SS for the piping and fittings. No corrosion problems, you can possibly use a thinner pipe wall, and better impact resistance for low-temperature.

The biggest problem I aware of with using stainless steel piping is the fit-up on the fittings and valves. And, you do need to use a shielded gas weld process.

I think it does have some possibilities.

You have to derate carbon steel when you get below -20F here in the States, or use impact tested material. Stainless helps you to bypass some of the other problems. So, you have many things to contend with.