There's a common misconception that shop-applied coatings are better quality than field-applied coatings. That's a myth, and here's why...
What Constitutes a “Shop” for Shop Coatings?
A shop is a building, right? And if a coating is going to be applied in a building, then the building has to have all the right ventilation, special devices for blasting in a designated room, and environmental and humidity controls, etc.
Just about everyone in the industry who knows about corrosion under insulation (CUI) and the equipment it attacks understands that the war against CUI must be fought on two fronts:
Today, every new piece of equipment that will be insulated and will operate in the CUI range now gets a coating. (Learn why in The Detrimental Effects of Wet Insulation in the CUI Range.) However, those who design it and pay for it to be fabricated and coated in the shop just automatically think that “shop” means a “controlled environment.” They may also assume that shop personnel are well-trained in coatings application and materials.
So right out of the box, if you have a controlled environment, you’re much more capable of controlling (and thus optimizing) the quality with which a coating is applied—right?
Nothing could be further from the truth. It's a myth, because there is no pure definition of a shop.
A shop is really just this: Anywhere except the site where the equipment will installed and put into service.
Makeshift Shops Abound
In real life, a shop could be a cow field with a road plowed through, and a cut for a trailer where people could go to get out of the rain. There could be an 8x8 cover over the bags of grit to keep them dry, or just a tarp thrown over the bags of grit. They can just blast and paint all day long out there in the middle of that cow field.
The client would never know the difference, unless there were very strict, specific requirements for third-party inspection and a reporting protocol that provided for the communication of those details.
When you specify coatings for shop application, you don’t know where the coating work is taking place.
Is a particular component of a piece of equipment or piping being fabricated and coated inside an environmentally controlled building? Or did they take that component and put it outside their building and blast it and coat it outdoors?
The owner doesn't necessarily know if a given component is being coated outdoors in a huge shipyard. For instance, a module for an offshore structure might be fully or partially assembled before a fireproof coating is installed. And, of course in that case, that module is very likely sitting outdoors within a mile of the ocean.
So a shop is really defined as anywhere except the site where the equipment will be in operation for the company that bought it. It often happens that the owner doesn't know exactly where the coating work is going to occur.
Engineers who sit in the offices and do the design work don’t really know everything that goes on in the coatings world. Are there third-party inspectors looking at the coating application that occurs in a shop? Only if third-party inspection is required by the specification.
Field Coatings aren't Necessarily Worse when Even "Controlled Environment" Shops Have Their Issues
Shop personnel are not necessarily well-trained in coating methods and materials. As an example, a huge grassroots (new build) was being constructed, which included thousands of fabricated geometrically complex spools of pipe. And all of these fabricated pipe spools were going to be coated in a shop in Arkansas—in February, March and April.
I was on the phone with these shop people and they told me, "Rest assured, we have a brand new state-of-the-art shop here. When we put on that inorganic zinc, you don’t have to worry. We are going to close up that shop and turn on the heat, and all of the inorganic zinc primer we put on that day is going to well-protected. Even though it’s chilly and wet up here in the springtime, you don’t have to worry."
I told them, "Please tell me you’re not going to do that. Inorganic zinc silicate cures with moisture from the air." In reality, some applicators even spray the newly applied coating with a water hose to ensure an expeditious and complete cure. (Intrigued by zinc silicate coatings? See IOZ Coating Surface Preparation Is Easier than You Think for more information.)
In conclusion, it's important to keep two things in mind:
- Coatings applicators don’t necessarily know what they are doing just because they have a shop.
- A shop is not necessarily a controlled environment.