1.0 Scope

This specification defines the minimum requirements to cover the selection, design, application, and inspection of glass reinforced plastic (GRP) linings to the bottoms of storage tanks.

2.0 References

The following documents are considered part of this specification. Use the edition of each referenced document in effect on the date of the publication of this specification.
In addition to the requirements of this specification, Lining Supplier's application specifications should be followed.

ASTM–American Society of Testing and Materials

ASTM C 581 Standard Specification for Determining Chemical Resistance of Thermosetting Resins Used in Glass-Fiber-Reinforced Structures Intended for Liquid Service
ASTM D 2563 Standard Specification for Classifying Visual Defects in Glass-Reinforced Plastic Laminate Parts
ASTM D 2583 Standard Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor

NACE–National Association of Corrosion Engineers

NACE RP0188 Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates
NACE RP0287 Field Measurement of Surface Profile of Abrasive Blast Cleaned Steel Surfaces Using a Replica Tape

SSPC–Society for Protective Coatings

SSPC PA 1 Shop, Field, and Maintenance Painting (Steel Structures Painting Manual, Ch 5 - Paint Application Specs.)
SSPC PA 2 Measurement of Dry Coating Thickness with Magnetic Gages (Steel Structures Painting Manual, Ch 5 - Paint Application Specs.)
SSPC SP 10 Near-White Metal Blast Cleaning NACE No.2-2000 (Steel Structures Painting Manual, Ch 2 - Surface Preparation Specs.)
SSPC VIS 1 Visual Standard for Abrasive Blast Cleaned Steel (Standard Reference Photographs) Editorial Changes September 1,2000 (Steel Structures Painting Manual, Ch 2 - Surface Preparation Specs.)

In the event of a conflict among the above listed standards or between the standards and other instructions listed in the specifications and drawing, it should be the Suppliers responsibility to notify the Buyer in writing for a resolution of the conflict prior to starting work.

3.0 Documentation

Temperature and service conditions within the storage tank should be provided by Buyer.
Personnel qualification - Lining installation should be undertaken only by Personnel qualified by experience in installing the type of GRP lining proposed.  Personnel should furnish details of below experience.

Proposal information - The following data should be submitted to Buyer for approval:

  • All product specifications, MSDS sheets and ventilation requirements.
  • Verification that the type of GRP lining proposed is suitable for the specified service conditions.
  • Repair procedures for damaged areas.
  • Reference panels (per Inspection and Testing section, Item 2 below) should be prepared by the Personnel.

Supplier should submit plans for Quality Assurance and Quality Control, the names of the coating inspectors, and their degree of training.

4.0 Materials

The resin system should be polyester, vinyl ester or epoxy suitable for the specified service conditions.  The resin system of choice should be 100 percent volume solids (solvent-less) epoxy if it is suitable for the service conditions, since this system is inherently safer to apply than the polyester or vinyl ester systems.  The glass content of GRP linings should be 20–30 percent by weight, excluding resin rich surface coatings. The coating materials used for tank lining applications are characterized by a variety of solvent and chemical hazards.  Where suitable for the application conditions and service exposure conditions, high solids or solvent-less epoxies are to be preferred since they are inherently safer to apply than styrenated polyester or vinyl ester coatings.

Prime coating for the GRP should be an amine or polyamide cured epoxy.

Caulks for filling or smoothing of steel surfaces should be based on the resin used in the laminate.

5.0 Design

Temperatures and service limitations for aggressive service should be determined by testing per ASTM C 581, unless satisfactory exposure experience at comparable conditions is clearly established.

Linings should be applied to all new aboveground storage tank bottoms where there has been a past history of bottom corrosion by the stored products.

The tank bottom lining should be extended to cover at least 18 in. (450 mm) of the first shell course.
Tank components such as equipment supports and flush draw-off nozzles, should be lined when specified.
Acceptable procedures for lining roof support column bearing areas are given in Figure 1 and Figure 2.

Floating Roof Tank Roof-Support Legs

Figure 1 - Floating Roof Tank Roof-Support Legs

Fixed Roof Tank Roof-Support Columns

Figure 2 - Fixed Roof Tank Roof-Support Columns

6.0 Surface Preparation

All sharp burrs, edges, and weld spatter should be ground smooth.

Metal surfaces should be blast cleaned to a near-white metal finish per SSPC SP 10.  The surface roughness should be per lining manufacturer recommendation.

Precautions should be taken to prevent contamination and damage during surface preparation and lining application.

7.0 Application

Application of primer, GRP, and seal coats should be per below Table.

Lining SystemComponent Application Method SpecificProcedures Coating Thickness
Primer(1) Spray 1 mil (25 mm) max. but not less than 0.5 mil
Caulking and coving(2) Trowel or spraySufficient to fill pits, eliminate surface irregularities and contour surface Minimum required to smooth and contour surface
GRP Lining Application Alternatives:Laminate Hand lay-upApply resin to tank bottom and then glass matRoll laminate to ensure wetting of glass mat, and elimination of entrapped airApply additional resin if needed 1 ply min. glass reinforcementJoints to have min. overlap of 3 in. (76 mm) 50–60 mils (1275–1500 mm)
SpraySpray application of resin/chopped glass rovingRoll laminate to ensure wetting of glass reinforcement, and elimination of entrapped air     1 coat
Glass Flake Lining Spray or trowel application of resin/flake glass Minimum of 2 coats 50 mils (1275 mm) avg.
Seal Coat(3)(Gel or Flood Coat) Spray Apply after high voltage holiday test Typically 7–10 mils (175–250 mm) avg.

(1)  Primer is not required if lining can be applied directly to freshly blast cleaned surface (SSPC SP 10) or if dehumidification is properly employed to hold the blast.
(2)  Prior to laminate application, caulking and coving is required to provide a smooth contour over surface, to eliminate irregularities (i.e., pits, weld seams, rivets, striker plate edges), and to provide a smooth transition at the chine.
(3)  Typically, an epoxy-phenolic seal coat is used at 7–10 mils (175–250 mm) with epoxy laminates.  High solids or 100 percent solids epoxy seal coats are often used at 10–20 mils (250–500 mm).  Polyester and vinyl ester resin laminates generally require a paraffin wax containing gel coat or a glass-flake-filled seal coat.

For deteriorated steel tank bottoms, with corrosion occurring on the soil side, apply two layers of 11/2 oz glass mat reinforcement for a total dry thickness of approximately 120 mils (3 mm).

Application should be per Lining Supplier instructions and SSPC PA 1.

After abrasive blast cleaning and/or priming, apply caulking to pits, weld seams, and the shell to bottom joint (chine).

After GRP laminate application, inspect for exposed glass fibers.  Sanding is required to eliminate exposed glass fibers.  Seal coat application is required after sanding.

8.0 Inspection and Testing

The term Inspector, used in this Specification, refers to the Buyer's Representative.  Inspector should be a NACE Certified Coating Inspector.

Personnel should prepare reference samples that meet all quality requirements.  These should be submitted to Buyer prior to execution of the work:

  • Samples should be 6 in. x 6 in. (150 mm x 150 mm).
  • One sample should be prepared of the complete system, to be used as a standard by Inspector for quality and finish of the completed work.
  • An additional sample should be prepared without a seal coat.  Inspector should use this sample as a standard for hardness, thickness measurements, and holiday testing.

Inspector should verify compliance with Supplier specification during the course of coating system application.  Work should not proceed to the next step in the system until the previous work has been inspected and approved.

8.1 Surface Preparation

The cleanliness of blasted steel surfaces should be verified using SSPC VIS 1.  The surface roughness should be verified per NACE RP0287.

8.2 Coating Thickness

Dry film thickness measurements should be made after application of each component of the lining system (primer, laminate, seal coat) in accordance with the procedure outlined by SSPC PA 2, with the stipulation that the Inspector should be empowered to make any number of measurements deemed necessary.

8.3 Application

All coatings should be applied within the environmental and timing constraints prescribed by Coating Supplier.

8.4 Visual Inspection of Coating

Visual inspection should be per ASTM D 2563:  Acceptance Level II.

8.5 Hardness Check

Barcol Hardness—The average hardness per ASTM D 2583 should be equal to readings made on the reference sample, and the minimum specified by Lining Supplier.

8.6 Continuity Test

The laminate should be tested for holidays, at the time directed by Manufacturer, with a high voltage holiday tester per NACE RP0188.  The holiday detector should be set at 5000 volts for 50–60 mils (1.5 mm) thickness and 10000 volts for 120 mils (3 mm) thickness.

Repaired areas should be retested and determined to be holiday-free.