One of the more interesting construction defects observed at a plant in Asia is a nearly universal application of coatings that did not cure.
As background, modern "paint" used in a power plant is a complex engineered product often applied in two or three layers. This is because each layer has a purpose. For example, inorganic zinc is often used as a primer, but not suitable as a top coat. Similarly, epoxy is used as a second coat, but not a top coat because it is poor at enduring UV unlike a urethane.
Each of the layers must be properly mixed, and usually is catalyzed with a hardener. The proportion of hardener to base product is very important. Too little, the coating never cures and perpetually stays soft. It's a failed coating. Another important factor is to keep water (rain and condensation) from the coating components. Water affects curing also.
At the plant in question, easily 70% of the coated plant (large coal plant) had coatings that were not cured. To test this defect, ASTM has a MEK (Methyl Ethyl Ketone) wipe test which roughly involves a clean cloth, a little MEK, and... Read more
Collosal. Left unrepaired...
EPC Contract indicated “the project site is subjected to moist and heavily polluted salt laden air”…
While the contractor took precautions to properly specify the coating systems, the surface prep and coatings application was flawed anyway. Normally, an effective shop (or field) inspection program will catch the problem early, and be resolved in favor an effective coating process. In this facility, there was extensive evidence that either no QC program existed or the inspector(s) were compromised.
After 18 months in operation, the coatings appear 15 years old. To varying degrees, most of the structural steel coating systems in the subject plant are in a progressive state of failure with the substrates rapidly and increasingly unprotected.
It was determined much of the steel coatings suffer from varying failure mechanisms. However, this photo is an example of improper surface prep (NACE/SSPC) and inconsistent dry film thickness , often with a top-coat greatly exceeding manufacturers requirements.
Minimal to no cost savings. Some time may have been saved if rework in the shops had been required.
Owner: Coating system will need an aggressive repair program as opposed to the anticipated touch-ups. Magnitude large but unknown.
HRSG Stack Welding
HRSG Stacks are subjected to accelerated corrosion where sulfur is present in the fuel (gas/oil). An engineered solution is to protect stack internals with a coating which contains glass flake. For the coating to adhere it must be applied on a properly prepared substrate (NACE/SSPC/Manufacturer’s Recommendations). Glass flake coatings cannot be effectively patched.
In this case, the stack field welds were not compliant with AWS D1.1, 5.24.4 (visual examination criteria), the construction contract criteria. This poor workmanship necessitated rework of the welds and stack coatings. Concerns include welder qualification, lack of weld inspection, lack of coatings prep inspection, and pervasiveness of defect (full length, all stacks). Additionally, the stack alignment lugs were not ground smooth in preparation for the coatings.
Another concern with unacceptable weld profiles in the stack is weld failure due to expansion and contraction of the stack during outage cycles and wind loads, especially in the presence of sulfur.
Blasting, weld repair, and recoating of one stack... Read more
Minimal. It takes no more time to weld properly, but perhaps some minor labor savings was gained with an unqualified welder
Owner: 2 month outage, revenue loss at $35,000/day =~$2,000,000. EPCC: ~$400,000 to repair welds and recoat.
Galvanized Hardware (Or Not)
When a plant is built in a moist, heavily polluted, and/or salt laden environment, corrossion protection is a serious consideration. At a minimum, hot dipped galvanized hardware (nuts, bolts, washers, clips, etc.) is usually specified for outdoor service.
In a recently visited new facility, agressive corrosion was exhibited almost universally on the hardware. What was discoverd is that wherever galvanized was specified, electro-galvanized, electroplated zinc, or zinc plated, (different terms, same thing) was substituted by the contractor. This results in a 3 to 12 micron coating that gives it a much lower degree of corrosion protection than hot dipped galvanized with an 85 to 90 micron layer of zinc.
IEC indicates these coatings degrade (in this environment) at 4-8 microns/year. It's then easy to see why there is so much agressive corrosion and advancing stages of metal loss after only a couple years.
In the rare cases where hot dipped galvanized was provided, it... Read more
Marginal material cost savings; No labor savings.
Contractor: Substantial cost (Labor/Material) to replace fasteners in bulk. Owner: Fasteners failing is significant. Electrical system risks increase over time.
Contractors sometimes take an extraordinary short-term view of their obligations.
At one plant EPR evaluated the owner's engineer had agreed to waive the contract requirement that all embeds were to be hot dip galvanized. The back-story is that the contractor managed to get late on anchor bolt delivery and wanted to skip the delay associated with galvanizing. It is also worth noting that this location was in a polluted location, in a hot humid region, on the sea. This simply means corrosion concerns are very serious.
The photographs were taken before the first unit even reached first fire. Already, the anchor bolts exhibit heavy corrosion and loss of substrate material at the threads.
Within a couple years of COD, it is conservative to expect the anchor bolts to be essentially non-existent. It's not clear how the foundations and structure will resist uplift forces without compromise and risk to the structure.
The "fix" at that time was to add galvanized nuts on top of the previously un-galvanized nuts. Sort of...
Non-Critical Path time was saved. Minimal cost.
Repair is difficult. Cost of structural failure could be high if a material uplift condition occurs.
A plant was evaluated that had an extensive desalination operation where seawater was flashed to create drinking water.
On the roof of the process equipment, there were insulated and uninsulated bays. One of several coatings problems was the difficulty with this arrangement related to coating selection. The top of the evaporator is essentially flat with bellies in the areas between the structural stiffeners. Water tends to collect in these locations and will not drain. In some cases, drain holes didn’t exist so water has been pooling for a couple years.
In these areas of the tops, the coating selection (urethane) was not suitable for water immersion and breaks down progressively. On the other hand, leaving the surface in epoxy would solve the water damage problem, but is not a solution because it is susceptible to UV breakdown. Therefore, the coating system as installed was not compatible with the propensity of the surface to hold and pool water.
This was not an academic concern, as there are indications the coatings had already failed. One photo shows the adhesion x-cut... Read more
Unknown, but significant.
In many developing country locations, a recurring problem is the mechanical damage to otherwise properly applied coatings due to handling abuse.
For most plants, structural steel is shop (off site) fabricated, loaded on trucks or ships, and delivered to the construction site for erection. This is an important process because it can become quite expensive and time consuming to field repair coatings. This can be even more true in locations with high humidity because a proper repair must be effected within the coating manufacturers indicated limitations. This is sometimes hard to achieve.
An owner should likewise be concerned because a repaired coating system is never as durable as the original coating. The first photo shows a typical "handling" problem. The subsequent photos show poor repairs and unrepaired damage. Both are so common, it seems normal.
One plant in Asia had structural steel and piping that was so abused with mechaincal damage that the plant looked 15 years old even before COD.
Nothing. It costs nothing to handle coated pipe/steel carefully.
If all teh repairs were affected, it would have cost severeral tens of millions of $.
Often field quality suffers from a lack of oversight; quality control, supervision, or owner involvement. Sometimes a contractor and owner set out to assure their interests are protected, but it fails anyway.
Using a large international source inspection firm tends to be where problems arise. Those firms use local inspectors to keep costs down by limiting travel. However, local inspectors are often the same people that visit particular shops and due to familiarity, a relationship develops which compromises the effectiveness of the shop inspection. Instances exist in remote areas where inspectors are relatives of shop owners. The main take-away, is that inspections by ineffective, conflicted, or technically limited personnel with no personal connection to your project is wrought with peril.
The opinion of the author is that if an inspection is worth performing by an owner, send your own people, or an inspector well known and hired directly. It will be more cost than outsourcing with a large international inspection firm, but it will be worth it.
At one facility, the contractor... Read more
$150k +/- and wasted time.
Coatings are typically shop applied and touched up in the field. On a large power station, there is considerable touch-up and it must be done correctly.
Briefly, as mentioned elsewhere in this Blog, coatings are not "paint", they are an engineered product that requires skilled personnel to apply properly. In this case there are three coats in the system. A zinc primer, epoxy mid-coat, followed by a urethane top coat. Details... No coating will stick to steel substrate that is dirty, too smooth, or otherwise not prepared to the coating manufacturers requirements. An epoxy mid-coat sticks well to a zinc primer, but does not stick to a urethane top coat. If epoxy is left without a urethane top coat, it deteriorates from UV. Urethane in most case needs to be applied over epoxy.
So, if a repair needs to be made, the existing paint needs to be taken off down to the primer, or mid-coat, depending on the damage. However, epoxy (mid-coat) cannot be "slapped on" as to overlap onto existing urethane. It will not stick. Also, coatings cannot be applied over corrosion or dirt; seems obvious... Read more
Varies by plant, but to re-perform is significant. If unrepaired, O&M is constantly painting, or lets plant rust.
Engineered coating systems are complex, as mentioned in other postings. When the manufacturer's recommendations are followed, these coatings are very good at preventing corrosion to the substrates. However, if proper prep, mixing, contamination control, etc., is not followed there can be many different defects that render the coatings useless.
One such defect is known as "pinholes". Often, or usually, this defect is not observable with the naked eye without magnification. It's almost like worms ate holes down through the layers of coating. Sometimes pinholes exist in a top coat, or maybe also the intermediate coating layer, but not penetrate the primer. In other instances, the pinholes may extend all the way to the base metal. If the coating is fairly new and pin point rusting is observed, chances are pretty good the pinhole goes to the base metal.
The remedy in such instances, is removal of the paint layer with the defect. If the primer also exhibits the defect, all the coating material needs to be removed. So, a "paint job" may look impeccable, but be a complete failure under... Read more
ROM - $25mm and a year of time by a well staffed painting contractor.