Weld repairs are often performed at chemical plants.
Equipment is broken! how do i fix it…
If you are going to try to restore it somehow in a short time, you will finally start welding.
There are several types even if you take one welding repair.
Both are dangerous, but it is required to make a judgment without spending time on site.
After reading this article, you will be able to choose the best method.
Weld repairs method
Welding repairs are mainly done in three patterns: padding, backing plate, and cutting.
I will introduce each feature.
Weld repairs
Build-up welding is a method of increasing the plate thickness by melting the welding rod directly into the defective place.
A defect means that the thickness of the base material is reduced.
For example, if there is a chip or crack, cut that part off.
Then the base material becomes thinner, so fill it with the weld metal.
A familiar example of welding repair is a dentist.
Weld repairs are very similar to caries treatment at the dentist.
- If mild cavities are found, they are scraped off and filled with resin.
- If there is a light chip in the base metal, scrape it off and fill it with weld metal.
Lightly shaving the surface before welding is just like dentist treatment.
- Minimum amount of welding
- Failure to repair may occur
- strength is low
Identification of defect location is important
It is important to identify the defect location in build-up repair.
This is because it is a method of directly repairing only the areas that need to be repaired.
When you look at the area to be repaired, you have to identify where the plate thickness is thin and unacceptable.
If a defect is found, it can be repaired, but if there is an overlooked part, corrosion will progress rapidly.
If you take it for granted that the dentist will find all the cavities and treat them for you, you’ll be sad if you miss them, right? It’s the same.
Cracks are identified by PT inspection, and complete corrosion is identified by board thickness inspection, but these inspections take time.
Smoothing is also required
Build-up repair welds the defective place, so it is not smooth.
After welding, in order to eliminate discontinuous parts, it is necessary to make it uniform with a grinder etc. and finish it to the same level as the plate surface of the base material.
The more areas to be repaired by overlaying, the more troublesome this process becomes.
just a makeshift
All welding repairs are temporary after all, but build-up repairs are especially strong.
This is an emergency repair.
Since the weld metal has deteriorated more than the base metal, even if the missing part of the base metal is replaced with the weld metal and the plate thickness is the same as the base metal, the same strength as a new product cannot be guaranteed.
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Weld repairs
It is used when the area is too wide to be repaired by overlaying.
In this method, a backing plate is attached around the part that is likely to be defective, and the base material and the backing plate are welded together.
The patch plate attached to the leg of the tank is sometimes called doubling (because it is double?), but the patch plate repair may also be called doubling.
Patch plate repair is equivalent to silver teeth in dentistry. It’s a translation that covers it.
- Do not damage the body
- Strength is reduced due to discontinuities
- Fastest repair time
Do not damage the body
In strong ad hoc welding repairs, the patch plate is the royal road of ad hoc.
Unlike cutting, the main body is not cut or scraped like a build-up, just closed from the outside.
The advantage of this is that there is a high possibility that the liquid inside the main unit will not leak during repair.
When repairing by welding, it is natural to remove the liquid inside the main body and wash it before repairing, but repairing without damaging the main body is a step above the rest.
- Hazardous materials may catch fire while welding
- Even if you repair it, if you start using it, the liquid may leak
You don’t have to think about these things for the time being.
If it is legal equipment such as equipment for hazardous materials, it is easy to explain to government agencies.
Naturally the strength drops
A patch plate is not as strong as padding, but it is less strong.
Even if the thickness of the backing plate is the same as the thickness of the base material.
because it is a lap joint.
This is because there is a discontinuity.
The theory is that discontinuities are weak.
Cutout Weld repairs
Cut-out repair is a method of cutting the defective part and butt-welding new metal.
Incision repair is equivalent to dentures in dentistry.
- High strength due to no discontinuities
- take time to repair
- You will think that you have restored it to the same condition as a new one.
Strength can be guaranteed to some extent
The strength is stronger than the patch repair.
This is because it can be repaired in the same shape as the base material by cutting.
Even in repair, it can be restored to a state that is quite close to new.
It is difficult to work on site because the equipment must be cut.
If you put your mind to it, you can do it on-site, but you probably won’t do it very often, especially in chemical plants.
I think even patch repair is scary.
Compared to the patch plate, there is a sense of uneasiness in the sense that the main body is cut.
I think that the people who repair it are also quite resistant.
should be thoroughly inspected
After welding repair, you have to do a solid inspection.
It is basic to do RT and PT.
RT is the equivalent of an X-ray examination by a dentist.
Do you take x-rays before and after dental treatment? It’s exactly the same idea.
In terms of dentistry, PT is coloring that checks for unpolished areas . . .
This inspection means that it has been restored to a usable state for the time being.
PT and RT are non-destructive inspection methods.
Should be replaced with a new one as soon as possible
When you can’t go without welding repair, it’s usually the life of the equipment.
Exceptionally, there are cases of defects during equipment manufacturing.
In any case, if a defect is found during operation, but you want to continue driving, we will repair it.
For that reason, you have to prepare a new one and plan to replace it at the right time.
It is necessary to carry out periodic inspections of repaired areas during operation.
It is dangerous to inspect it after repairing and then leave it until the regular replacement.
If you go to the dentist, once you get cavities treated, it’s the same as not going to the dentist again for a while.
I repeat,
Weld repair is a stopgap.
When an abnormality occurs, let’s balance emergency measures and essential measures!
To learn the basics of welding
To learn how to repair welds, first understand the basics of welding.
There are various books, but for example the following books are useful.
It would be nice to have a photo that you can see with your own eyes.
There are other good teaching materials in videos, but the advantage is that you can study offline.
lastly
I explained the welding repair performed at the equipment of the chemical plant.
Meat plate, doubling, backing plate.
Even if you decide to do welding repair, there are several types and there are merits and demerits.
Because the decision time is short, I want to be able to use it properly!
Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (The comment section is at the bottom of this article.)
*I will read all the comments and answer them seriously.