Weld Repairs and Ball Valves for Hydrocarbon Handling

Because that make it a repaired substandard part,

Any thing that you try to do by out of your normal process flow, may produce a sub-standard product, Since alternate process may not be validated for product quality.

The heat of the weld will change the forged properties of the metal.

"weld will change the forged properties "

This possibility could happen to any type of valves, but for ball valves in specifics, I believe this caution means more.

The mating rings for ball are normally made of high polymers like PTFE. These rings are are located very closer to flange socket where weldment is deposited. So these rings might get burned off.

hi there, normally when you are talking about hydrocarbon it will be ether in gas plant which going to use (NG) natural gas or refinery.

two things you are looking at.

1.fire because it's flammable.

2.you can't guaranty how it will react.

for this two reason normal recommended to do formoniting and climb(not so good with gases not recommended) and climb.

however both of the solution are temporary action till you fined another valve.

Besides the fact that sealing rings etc will deform or break due to the extensive heat, also the valve body will deform because of the heat concentrated in one spot. Because of this deformation, the valve is not tight anymore.

Also, when you do weld-repairs on valves, the specifications of the valve as it was installed are not valid anymore, and the valve should be replaced. In very rare cases (specific type or size of valve, body material, etc) exceptions can be made, but you'll need permission for this.

I have seen weld repairs on ball valves we supplied for a petrochemical plant. This was done by the manufacturer of the valve at the time of manufacture so it is not prohibited as far as I can see. If you are talking about a repair to a valve by a manufacturer or rebuilder of a valve, I don't believe you are correct.

The answerers seem to think you mean on-site repair of an in-service valve by a maintenence crew. If that is the case, I'd agree with all of their statements but to say generically repairs are not allowed, would not be correct.

I have seen valve manufacturers make valve body repairs for ball valves in house many times. The manufacturer knows exactly what the alloy is and aslo has the appropiate weld filler metal and welding procedure as well as the capabilities to machine the valve back to tolorances and porperly post weld heat treat the valve. I would think that the client may have a rule against weld repair on ball as well as other types of valves because of the liability issues. The valve manufaturers also would not want someone else making field repairs to thier valves because they like to get the money for the repair instead of some other company. Also they cannot afford to warrent another company's repair and with hydocarbons the warranty is very important to the client and the manufacturer both in case the valve repair fails. Many times a valve will have seals or have some hardened or chemical resistant material inside that can be damaged by the heat from welding. Basically it just isn't worth taking the chance. IMO

pipewelder

I thought he mentioned repairing on site or in our own workshop. If manufacturer's will repair a valve by welding the body and afterwards recertify the valve, there is no problem to repair the valve body by welding. In the offshore in NW-Europe repairs on valves by means of welding is not allowed.

Hi, Ruby!

I agree with ozzb. A valve is not just a flow control and metering mechanism, it is also a safety device.

When a weld is made to any part of it, the material properties of the valve become changed both on and around the weld.

While careful welding and grinding may accurately approximate the original, its integrity is no longer as reliable as when its components were originally forged intact. Using a weld-repaired valve would be using substandard equipment.

However, if you have to do it because there is absolutely zero money for replacement, choose a same-style, same-sized valve from your equipment that has a low expectation of operating stress, and replace the repaired valve with it, replacing the less-stressed valve position with the repair job.

This happens in the real world. Unfortunately, some shipping companies 'foreign-flag' their vessels and hire less costly crews to run them. They are typically given next to nothing for a completely inadequate budget as far as repairs and maintenance is concerned; and the crews must undertake repair decisions using this kind of replacement-part model. The crews become superb make-do-ers with technology that would make McGyver jealous. (For those not in the 'know', McGyver was a TV serial hero who could innovate his way out of amazing tight scrapes with nothing typically more than a paper clip and the lint in his pocket, so to speak.)

After a period of time during which the ship has been repaired --almost literally-- with string and chewing gum, it is returned to its original flag and sent to a repair dock for refitting before being sent out again.

Mark

the welding process changes the crystaline structure of the forged metal and usually results in a weakened area adjacent to the weld area.