Stud Bolts, Nuts, Screws, Threaded Rod & Washers
Aluminium Ceramic Coated Fasteners of carbon steel and low temperature carbon steel are manufactured in accordance with Shell MESC SPE 81/010 specification in order to provide corrosion protection. The coating system shall be spray-applied aluminium ceramic (cermet, e.g. SAE AMS 3126) and cured to provide a non-stick and non-porous inert finish. The thickness of the coating shall be minimum 25 microns (1 mil) but not more than 38 microns (1.5 mils) with continuous and pinhole free coating. The coating system shall be applied in one coat to provide pinhole free uniform coating.
The aluminium ceramic coating covered in this specification
is intended for atmospheric exposure in a highly corrosive coastal
and marine environment with high airborne chloride content. The
Aluminium Ceramic spray coating shall have temperature
resistance from minus 50 ⁰C to 400 ⁰C (minus 58 ⁰F to 750 ⁰F).
Aluminium Ceramic Coating on fasteners can be of two types :
The proposed steel substrate of fasteners shall be checked for dimensional and thermal stability at the bake temperature required before the surface preparation.
All edges shall be ground to a minimum radius of 2 mm (0.078 in) or as otherwise agreed with the Principal.
Ferrous metals shall be preheated before abrasive blast cleaning in order to retain the protective oxide formed. Immediately prior to blast cleaning, surfaces to be coated shall be heated to 343 °C - 371 °C (650 °F-700 ⁰F) for a minimum time period of 90-minutes in order to decompose any remaining contaminants.
Cleaning of surfaces shall be done by dry blast cleaning according to ISO 8504-2 or NACE-2 or SSPC SP10. The blast cleaned surface shall meet the requirement of visual standard of Sa 2½ of near white metal finish in accordance with ISO 8501-1 or NACE 2 or SSPC SP-10 at the time of coating application.
The surface profile and the anchor pattern for steel surfaces shall be in accordance with recommendations of the coating applicator. If not specified, the surface profile shall be an anchor profile of 12.5-25 microns (0.5-1.0 mils) trough to peak.
The maximum total allowable soluble salts level on the surface is 25 mg/m². The salt level shall be assessed in accordance with ISO 8502-6 and ISO 8502-9.
The application shall be done by spray method such as manual spray, automatic spray and electrostatic spray methods. The applicator shall be able to demonstrate the smooth uniform coating, thickness and pinhole free surface of cured coating.
The curing shall be done at 400 ⁰C (750 ⁰F) for minimum 65 minutes in a circulating-air furnace.
The cured coating shall be burnished by glass bead peening or other suitable means.
Testing shall be conducted on the coated bolt from the respective lot. However, when coated bolts are of such configuration or size as to be not readily adaptable to specified tests, separate test specimens, of the same generic class of alloy as the parts being coated, cleaned, and coated with the parts being represented may be used. For adhesion, thickness and conductivity tests, specimens shall be panels approximately 1 x 25 x 100 mm (0.04 x 1 x 4 in).
Where accessible, the coating surface shall be checked with a 10X magnification. Look for smoothness, color, gloss, blistering, pinholes, or mud-cracking. No defects shall be visible.
The cured coating film integrity (lack of pinholes) be tested using a low voltage holiday detector /spark test at 90 V with wet sponge on a conductive metal surface in accordance with NACE SP0188. No pinholes shall be present.
The curing test shall be carried out according to ASTM D 4752. Rub cured film 50 times (back and forth) with a soft cloth saturated in MEK. Only surface pigments should show up on the cloth. The film should not be soft or tacky; otherwise the film was not completely cured.
The pencil hardness of the cured coating shall be 8 H tested according to ASTM D 3363.
Coating dry film thickness (DFT) shall be measured by means of a thickness meter based on eddy-current or electromagnetic techniques, in accordance with ISO 2808, methods 7B (magnetic-flux), 7C (magnetic-induction) or 7D (Eddy-current). The coating thickness gauge shall be calibrated daily in accordance with SSPC-PA 2. The magnetic ‘banana’ type gauges shall not be used.
For parts with irregular surfaces, place a piece of foil in areas of the part that would be difficult to measure with the gauge. After curing the part, remove the foil and measure the film on the foil with a micrometer. An alternate method is to spray a flat panel at the same time the part is being coated to approximate the film thickness on the part.
The adhesion test shall be carried out by Crosshatch test method in accordance with ISO 2409, Class 0 for thin layer coating systems before testing below.
Boil, cool, and dry piece for testing. Using a new single-edge razor blade, make eleven (11) parallel cuts in the film approximately 2.4 mm (0.1 inch) apart. Repeat at right angles to form 100 small squares. Press a strip of 25 mm (1 inch) wide transparent tape over this area and rub firmly with a fingernail to get maximum contact. Pull the tape off firmly and rapidly without jerking. After removing this piece of tape, put another piece on at right angles, and repeat the procedure. Film with good adhesion will not show any squares removed (although some corners or edges may be lifted). If 20% or more of the squares are removed, the piece has failed the test. The adhesion test also indicates complete cure.
Conductivity testing shall be performed to ensure that electrical resistance is no more than 5 ohms per 25.4 mm (1 in), determined by means of a Wheatstone bridge or suitable direct reading ohm-meter operating on direct current with a minimum distance of 25.4 mm (1 in) between probes. The contact areas of the probes shall be of such configuration as to make intimate contact with the surface without penetrating the coating.
The cured coating shall be stabilized between -50 ⁰C (-58 ⁰F) and -40⁰C (-40⁰F) temperature for 24 hours and taken out from the deep freezer. The visual inspection shall be done on coating condition to check for any cracking and corrosion by 30X magnifying glass. Check for adhesion of the coating according to ISO 2409. The test shall be performed on ASTM 320 L7 type bolts coated with aluminium ceramic coating.
The coating shall be exposed to 400 ⁰C (752 ⁰F) for 1 hour in a suitable autoclave oven and then cool it down to ambient temperature. The visual inspection shall be done on coating condition to check for any blistering, cracking and corrosion by 30X magnifying glass.
Repeat the adhesion test of the coating after the heat resistance test according to ISO 2409. The test shall be performed on ASTM 320 L7 type bolts coated with the aluminium ceramic coating.
A corrosion resistance test for coated bolts shall be carried out in accordance with ASTM B117 (salt spray test) for the time duration of minimum 1000 hours.
| Alloy & SS Steel Bolts to ASTM A193 | Shell MESC SPE 81/001 |
|---|---|
| Carbon & Alloy Steel Nuts to ASTM A194 | Shell MESC SPE 81/002 |
| Standard Practice for Operating Salt Spray (Fog) Apparatus | ASTM B117 |
| Standard Practice for Fastener Sampling for Specified Mechanical Properties and Performance Inspection |
ASTM F1470 |
| Discontinuity (holiday) testing of new protective coatings on conductive substrates |
NACE SP0188 |
| Coating for protection of fasteners | NACE Item No. 24232 |
| Paints and varnishes – Determination of film thickness | ISO 2808 |
|---|---|
| Preparation of steel substrates before application of paints and related products – Visual assessment of surface cleanliness &– Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings |
ISO 8501-1 |
| Preparation of steel substrates before application of paints and related products – Visual assessment of surface cleanliness – Part 3: Preparation grades of welds, edges and other areas with surface imperfections |
ISO 8501-3 |
| Preparation of steel substrates before application of paints and related products – Tests for the assessment of surface cleanliness – Part 6: Extraction of soluble contaminants for analysis – The Bresle method |
ISO-8502-6 |
| Preparation of steel substrates before application of paints and related products – Tests for the assessment of surface cleanliness – Part 9: Field method for the conductometric determination of water-soluble salts |
ISO 8502-9 |
| Preparation of steel substrates before application of paints and related products – Surface preparation methods – Part 2: Abrasive blast-cleaning |
ISO 8504-2 |
| Paints and varnishes – Cross cut test ASTM D4752: Standard practice for measuring MEK resistance of ethyl silicate (inorganic) zinc-rich primers by solvent rub |
ISO 2409 |