Methanol Leaks and Gate Valves with Hastelloy Trim

Changing the MOC of the valve trim cannot affect its leak rate as much as correcting the alignment and any wear of the components!

Is there a temperature change issue inside the valve that can affect the dimensions and positioning of the components inside it?

Why do you not install another valve piping and have two while one stays open to a chamber to act like a reserve tank which would deplete when the second valve opens and the first is closed. In this way the leak should stop and the result will be no real change in the Methane flow. One piping is a relief valve service to maintain a lower pressure on the main valve.

So is the leak at the stem or the bolted joint.

Could this be caused by external corrosion or tampering of the turn screw?

If external corrosion maybe the coating is inadequate, newer coatings certified for newer pipes and valves are available, change of a old coating valve and re-coating it with a new coating might be less expensive.

If there is a temperature change issue inside the valve, it then could be a coating issue, the coating is to keep the material of the pipe and valve from altering due to a change in temperature which would be a difference between the external temperature and internal temperature. Manual operators could have caused the coating of the old valve to dislodge and be interference in the shaft else vandalism would be a issue.

This should Stop Methane Passing or Leaking in a Gate Valve.

I think you need to read the question again!

the problem is inherit with the gate valve. the seat of the gate valve, i assume, is also metal. the torque required to seat the valve properly is much higher than a soft seat. since your service is a clean service and not high temperature (, methanol at 95C, could be a two phase?), you resolve the problem by going with a soft seat like PTFE.

hastelloy should not affect the leaking issue.

You don't specify if your valves are hand or otherwise operated (motor...)

Neither the type of gate valve (solid, flexible or split wedge, parallel sided with internal wedge, i.e Anchor Darling type...)

Anyway, stellite is a very common material for gate valves in the wedge to seat contact faces, independent on the body material, which in your case is carbon steel but its also common for stainless steel.

Of course to make a seal between two metal surfaces you need two things: flat faces (no radial scratches on the hard faced zones of seat or wedge) and a minimum stem thrust. If no thrust enough (for example in the case of handwheel operated and high pressure) you can have leaks because you don't have the minimum contact stress to assure tightness.

If motor operated and hard seated (torque switch controlled) then probably you have the seat damaged and need just refurbish it (by lapping may be).

There's no difference relative to the fluid you use because it doesn't attack any body or trim material.

P.D. For a gate valve don't use plastic or any other resilient trim materials.

Kind regards

How much leakage? A single gate valve (as compared to a double block and bleed configuration) is NEVER considered suitable for isolation. Some leakage is almost certain with such a low viscosity liquid. Have you examined the seat cavity to see if any debris has accumulated? Often, small particles of ?? will collect in the wedge pocket and prevent the gate from fully closing. Orienting the valve stem down will minimize debris problems. Also, to what leakage spec did you purchase the valves? Standard tolerance valves ARE NOT (leak tight). If you want (need) very low leak shut-off, you will have to go to soft seated butterfly type. Metal -to-metal wedge seating (cast iron, cast steel, Stellite, Hastelloy, chrome) is not suitable for the non-lubricating characteristics of methanol. Scuffing of the seat surfaces is a virtual certainty, and leakage after the first closing almost guaranteed.

You may want to consider using a double seated gate valve with a vented, concave gate. Such a gate valve seals on both sides of the gate, has machined seats that mate with the matching body seats, and has a vented gate cavity that lets the operator know if either seat begins to leak.

In response to a nother response methanol boiling point is 64.7 deg centagrade, so at 95 deg and atmospheric pressure it is a vapor, not a liquid.

We used a zero leakage Parallel Disc Pressed Butterfly Valve for a methane application in Canada and all we specified was WC6/Stellite overlay,the gate valve will not perform with what you want,Butterfly Valve.

Good solution, changing the valve has a terrific effect. No Stem!

I found a answer to the question, it has to be relative to your specific product. Seriously look into it deeply to resolve the situation of the atmosphere surrounding the exterior of the piping.

I realize that the Gate Valve may be of good quality but there are still instances that can cause problems esp. at the stem. With each stroke of the valve stem downwards, molecules of water vapor in the atmosphere are entrapped in the peaks and valleys of the stem's microstructure, and are drawn down into the secondary packing rings. As the stem retracts, a molecule of the permeated fluid may be pulled up into the packing rings. If the molecules of moisture and permeated fluid come into contact, a "solution" may be formed. This "solution" will be highly "concentrated" and can be highly corrosive. If the stem material is vulnerable to the concentrated solution, chemical attack of the valve stem in the mid-range of the packing zone may begin. Once this mechanism begins, the result may lead to premature stem failure.

When dissolved in moisture H20.

hydrogen sulfide + water ---> Hydrosulfuric acid; a weak acid even when concentrated.

H2S + H2O H3O + + HS –

chlorine gas + water --> hydrochloric acid; + oxygen gas a very strong acid even when not concentrated

2Cl2 + 6H2O 4H3O + + 4Cl – + O2

acids are formed in both cases. The hydrosulphuric acid is a weaker acid that 316 SST is sufficiently corrosion resistant against. However, the hydrochloric acid is a strong acid that corrosively attacks 316 SST. Both increased pressure and temperature accelerate the corrosive mechanism. However, the overall rate of corrosion is very low as the permeation rate is very low. Chlorine gas is an example of a fluid where alternate stem construction of Hastelloy C-276 will maximize unit life and proper functioning of the secondary stem seal design. Use of alternate stem material is subjective and dependent on many various factors, and is like most CPI decisions, based on value judgement.

NOTE: The corrosive effects are primarily limited to the stem/secondary packing rings zone where moisture and acid molecules interface.

Chemicals Known To Permeate TFE

* Fluids where alternate stem materials are recommended.

** Corrosion effects on metallic parts unknown.

* Ammonium beryllium fluoride

Benzene

* Bromine

* Bromine (water - 3% saturated)

* Bromine chloride

Butane

Butyl bromide

Butyl chloride

Butyl phenol

Butylene (Butadiene)

Carbon bisulfide

* Carbon tetrachloride

Chlorinated phenol

* Chlorine (5% in CCl4)

* Chlorine dioxide

* Chlorine

* Chlorobenzene

* Chlorobenzyl chloride

Chloroform (Trichloromethane)

* o-Dichlorobenzene

Dichloroethane

Diethyl ether

* Ethyl benzene (acidic)

Ethyl ether

Ethylene chloride

Ethylene dibromide

Ethylene dichloride

* FREON Fluorocarbons

Hexane

* Hydrobromic acid

* Hydrochloric acid

* Hydrofluoric acid

Hydrogen

* Hydrogen chloride

* Hydrogen cyanide

* Hydrogen fluoride gas Hydrogen sulfide

* Iodine (gas)

* Iodine (Tincture of)

Methane

Methyl chloride

** Methyl chloroform

** Methyl chloromethyl ether

Methyl ethyl ketone

Methyl isobutyl ketone

** Methylene bromide

Methylene chloride

Naphtha

Naphthalene

Nitric acid

Nitrobenzene

Nitromethane

Oxygen

Perchloroethylene

Phenol

* Phosgene

Potassium cyanide

Propane

Propylene oxide

Styrene monomer

Sulfur trioxide

Sulfuric acid

Tetrahydrofuran

Toluene

Toluene (25%) + kerosene (75%)

1,1,2-Trichloroethane

Trichloroethylene

** Trimethyl propane

Vinyl chloride monomer (liquid)

** Vinylidene chloride (monomer)

Xylene

Charles Jones,Thank you your discussion is extremely informative and very helpful.

And what's the corrosive product of reaction between methanol and water? You've included a great list of products but it doesn't includes methanol.

Even in the case a few water molecules get inside a 32" gate valve what will be the concentration of such "corrosive" product? Will then attack a stellite seat?

Very good information but irrelevant to the case.

Kind regards

I believe that Keith Bowers has given you some great advice based on my 40 years in Nuclear submarines,Paper Mills and the last 32 in Chemical plants.The following is my belief for Solvent Valves of ALL types based on maintaining fluid systems.This is what worked for us.I know as I was one of the the mechanics.

The seating area of a Gate Valve in any position but handle down,is a great place for trash to collect.Nearly all but the most expensive Gate Valves seep and leak.Some a little,some a lot.Cheap Gate Valves caused more incidents in my 40 years in maintaining systems than all other Valve types put together.Several times causing MAJOR incidents including injuries to people,small and Major fires,small explosions and massive property damage to the plants.I was there! They are cheap to purchase,but very expensive overall beside a good Ball or Globe Valve.They are the most miss-used valve that I have seen in the USA and abroad.

We found ball and Plug valves with Teflon seats to be great all position stop valves.Most are repairable.Certain ones can be quickly repaired in place without removing the valve from the systems as all worn parts come out of the top of the valve for replacement with new parts!These and Gate valves are made for on and off,not for flow control.Any attempt to use them for flow control often will cause erosion as will a leak!Some tapered "Plug Valves" have been made to be able to tighten down or adjust for wear when they start leaking.A thin gasket added on top of the plug or seat to push down has often lasted for many more years.

For flow control or trashy systems,Globe valves with the "right seat" to be great all position valves.

I do not know how clean your system is or any of the system facts.

The correct Gate Valve,installed correctly in the correct place is fine.The shame is that this is very uncommon,even on prints drawn by professionals.Check it out in your plant!It may save you some grief."Incorrect" has certainly caused enough in my life.Alfred

The problem with the gate valve in may instances is that it takes up to much real estate,with severe service we have been using this new PDP Butterfly valve that is more reliable,more versatile and smaller in size and weight.It's patented shutoff is new and unique to our valve industry.

I very much doubt that the change of material can be the cause of leakage. Other factors may influence: is the valve lapped properly (though gate valves don't tend to have lapping problems)...? Has pressure increased? And temperature?