Linings (Chap 15- API RP652) Flashcards
What is a holiday?
discontinuity in a protective coating that exposes unprotected surface
What is anchor pattern
surface profile or roughness
What is mil?
.001 inches
25.4 um
what is a lining
material applied to the internal surfaces to act as a barrier to corrosion and/or product contamination
thick film lining mils?
thickness of 20 mils
thick film reinforced lining
thick film reinforced with chopped glass fibers and others (often used on aged floors that incurred corrosion and are rough and pitted and thinned bottoms)
thin film lining thickness
less than 20mils or 0.51 um, use for little corrosion (not suitable for heavily pitted tanks)
When is lining neccessary?
- If inspection shows that min thickness of a bottom steel plate is less than 0.1 “
- If corrosive condition exist ( caustic corrosion, chloride SCC, caustic SCC, sulphuric acid corrosion)
Advantage of thin film?(6)
- initial cost is less
- easier to apply
- can be > 20 years if applied properly
- good flexibility
- allow for more accurate MFL scans
- Easier to remove
advantage of thick film reinforce lining(7)
- easier to achiever coverage over rough, pitted steel and surface irregularities
- ability to bridge future penetrations
- resistance to mechanical damage
- laid by hand or chopper gun
- few or no discontinuities to repair following the holiday test
- > 20 years
- provides resistance to moisture permeation
Advantage of thick film UNreinforced linings(9)
- built up to 100 mils in a single coat
- better coverage over rough surface
- generally applied in a single coat, no issues with contaminations between coats
- provides resistance to moisture permeation
- > 20years
- promotes a reduced tank T/A schedule
- reduce labor cost compared to multi coat think fil or labor intensive reinforce thick film linings
- few or no discontinues to repair following holiday test
- fast curing and can be put back in service after 24 hours at normal ambient temp
What are some causes of tank bottom lining failures?(9)
- inadequate surface preparation
- lack of cleanliness (oil, tar and grease must be removed prior to abrasive blasting)
- Presence of salt
- environmental condition during application, (temp at 5F (3C) above the dew point temp , relative humidity should be below 80% at steel surface
- failing to meet the manufacturer requirement regarding recoat intervals. subsequent coats must be applied with recoat interval
- improper mixing
- insufficient coverage (not enough thickness)
- too much paint (too much thickness)
- inadequate curing time
- failure to remove discontinuities from the surface ( esp for thin film)
Holiday testing?
detect discontinuities - thin film should apply at low voltage wet sponge detector
Type of bottom lining materials?
found in tapes 1 and 2 in API RP652 Thin film (mostly epoxy based) Thick film (reinforce) - Polyester mix , vinyl ester, epoxy Think film (unreinforced, same as reinforce)
Surface prepartion?
SP5 - white metal finish = desired
SP10-near white metal finish = minimum
SP11- for small areas to avoid nearby damage
What is require anchor pattern for SP?
1.5 to 4 mils and increase with thickness of the lining, important to achieve anchor pattern is sharps and angular
Issue that will affect application of lining(4)
- lining system - following recommendation of manufacturer (sufficient curing, holiday testing)
- guideliens for lining application- procedure establish proper on site storage conditions mixing applying and guiding.
- temperature/humidity control - surface temp at least 5F (3C) above the dew point temperate and humidity less than 80%.
- lining thicknesss- wet film thickness measurement to be made as lining is being applied
- lining curing - thin film lining are higher voc than thick film, proper cure time and temperature.
What is lining relation with API653?
Table 4.4 of 653 states that if a lining thickness-thick reinforce >.5 inch, then the min bottom plate thickness is 0.05”.
Also next inspection interval the internal corrosion rate (StPr) of a tank with internal lining = 0
Pitting caused by concentration cell corrosion of a bare steel tank bottom may be as high as
80 mils per year
Sulfate-reducing bacteria (SRB) corrosion is universally recognized. The physical presence of bacterial deposits can promote aggressive ________
mechanism.
Pitting by corrosion similar to concentration cell corrosion
SRB colonies derive energy from the reduction of sulfates to sulfide
which _______.
Is corrosive to steel
Erosion-corrosion may occur in wastewater treating or mixing tanks where ___ is present
Soil or small abrasive aggregate
Flexing of the steel tank bottom may cause ______.
An internal bottom lining to fail by cracking
In old tanks, which of the following may complicate the problem of poor coverage?
Chemical contaminants
Why must all linings be resistant to water?
Water must be present at the tank bottom for electrochemical corrosion to occur
Which of the following type of lining would be used for a tank bottom containing water, crude oil, distillates, and gasoline at 150ºF
Thick film isophthalic polyester
Which of the following type of lining would be used for a tank bottom containing water, distillates, crude, and gasoline at 195º
Thin film epoxy with an amine curative
One advantage of thick-film lining is _________.
It can provide sufficient strength to bridge over small perforation in the tank bottom
Special consideration must be given to what area of the tank bottom with regard to thick-film lining?
The coving at the transition from the tank bottom to the shell
Storage tank bottom linings generally cover the entire tank bottom and extend ________ up the shell of the tank.
18 to 24 inches
For thin-film lining systems, application of ______ coats is often required
to achieve the desired film thickness
2 to 3
For thick-film lining systems, ______ coats may be required to obtain
the thickness of the desired lining.
1 to 4
When only internal corrosion is taking place, regardless of the age of the
tank, ______ thick linings may be used
35 to 55 mil
Besides the corrosion history and the potential for corrosion, what two exceptional circumstances must be taken into account during the selection o a tank bottom lining?
Elevated temperatures and product purity
What type and thickness of lining can be used for older tank bottoms that have corroded both internally and externally?
Glass reinforced - 80 to 120 mil
To facilitate inspection and to ensure good adhesion of the lining, surface preparation should extend _______ beyond the area to be lined.
SEVERAL INCHES
To ensure the lining meets the specification, it should be inspected during ___ and ___.
Application and upon completion of the work
All lining inspectors should demonstrate a thorough knowledge of lining and coating practices or be _____ certified.
nace
How is holiday testing of thick film linings accomplished?
Holiday testing of thick film linings shall be carried out with a high voltage detector in accordance with NACE RP-01-88
Before deciding how to repair a lining, the cause and extent must be established. In addition, what three possible failure modes must be considered as possible causes of lining failure?
Mechanical, improper installation, environmental
when to inspect film thickness of tank bottom linings?
before and after bottom is dried
holiday testing for thick liner?
high voltage
