BS ISO 18070:2015 pdf download – Corrosion of metals and alloys — Crevice corrosion formers with disc springs for flat specimens or tubes made from stainless steel
5.1Specimen specifications
Both flat specimens and tubes made from stainless steels can be used as specimens in the crevicecorrosion formers specified in this International Standard.The specimen outer surface area shall be atleast 100 cm2.
NOTE1 A squared specimen with a centre hole is preferred since the distance between the anode and cathodearea might be critical in solutions with low conductivity.
NOTE 2lf an electrode potential is applied, a smaller specimen can be used.
5.1.1 Flat specimens
A hole, 7 mm in diameter, shall be drilled in the middle of each specimen.
NOTE To hang up of specimen and for electrical connection, a small hole can be drilled at one end of thespecimen.
A hole, 7 mm in diameter, shall be drilled in the middle of the tubes in radial dimension.The hole shallbe drilled at both sides of the tube allowing a bolt to be inserted in the hole without alignment.Thelength of the tubes shall be at least 30 mm.
NOTE To hang up of specimen and for electrical connection, a small hole can be drilled at one end of thespecimen.
5.2Surface preparation of the specimens
5.2.1The surface finish shall be as reproducible as possible.Any test surface may be tested but it isrecommended that all surfaces, including cut edges and drilled holes, shall be abraded down to at leastP120 grit paper, according to ISO 6344-3.Care shall be taken to avoid overheating the surface.
NOTEultra sonic cleaning after abrading can be used.
5.2.2 After abrading and cleaning, the specimens shall be left in air at a temperature higher than thedew point temperature for at least 24 h before testing, to be able to form a stable oxide.
5.2.3 The specimens shall be cleaned immediately prior to immersion in the solution by degreasing.rinsing in high-purity water with a conductivity less than 1 uS/cm, (ISo 3696, grade 2) followed byethanol or a similar solvent and air drying.After degreasing, care shall be taken not to contaminate thetest surface of the specimens.
6Crevice former and assembly6.1General
Both flat specimens and tubular stainless steels can be used as specimens in the crevice corrosionformers specified in this International Standard, see Figure 1 and Figure 2.
6.2Disc springs
Disc springs with a linear force versus deflection relationship shall be used. The relation betweenthe force and deflection of the setup of the disc springs shall be known.For disc springs according to DIN 2093, the deflection that corresponds to 0,9 kN is 0,9 mm; for other disc springs, the deflection that corresponds to a force of 0,9 kN shall be measured with a tensile machine. NOTE In the USA, disc springs are called Belleville washers.
6.3 Crevice former
The crevice assembly is of the spring loaded type. Nut, bolt, and washers (rings) are made from titanium. The thickness of the washers is between 2 mm and 4 mm. Outer diameter of the washers shall be at least 20 mm and the inner diameter at least 5,2 mm. Bolt diameter shall be 5 mm (M5 threads) and the length is about 75 mm. A PVC (polyvinyl chloride) or PE (polyethylene) hose is mounted around the bolt, from the head of the bolt to the crevice former at the nut side, to prevent electrical contact between specimen and the assembly and to centre the rings, disc springs, and specimen. A schematic drawing of the assembly for flat specimens is shown in Figure 1 and for tubes is shown in Figure 2. A ring of inert polymeric material, like PTFE (polytetrafluoroethylene) is mounted to centre the disc springs, as shown in Figure 1 and Figure 2. The disc springs are made of titanium or nylon coated steel. The disc spring shall be according to DIN 2093 or with a calibrated deflection-force relationship. A set of four springs is used to obtain a load of ~0,9 kN (this corresponds approximately to a torque of 3 Nm, with the crevice assembly applied using DIN 2093 disc springs). The crevice formers are made of PVDF (polyvinylidene fluoride) and can be used up to 95 °C. The outside diameter is 20 mm and the inside diameter is 7 mm and height is 15 mm.