Instrument Material Selection Philosophy

Instrument Material Selection Philosophy

All materials and equipment furnished shall be new and unused, of current
manufacture and the highest grade and quality available for the required service,
and free of defects.

Materials shall be selected with regard to the following criteria:

1. Suitability for the specified process conditions, with SS 316 as the minimum
for use outside pressurized rooms, except for salt-water service.

2. Suitability for the corrosive effects of the atmosphere.

3. Galvanic compatibility between dissimilar materials, with isolating bushes,
plates, used where necessary to prevent corrosion due to galvanic action.

4. Wherever process condition demands NACE quality Instrument fittings, the
same shall be provided as per NACE, latest standard with appropriate
material. For non NACE application, material for fitting shall be appropriate for
relevant process fluid with SS-316 as minimum.

5. Company approval shall be obtained for the use of aluminium for any
instrument component. Aluminium may only be used if no other suitable
material is available but shall not be used for any component in contact with
the process fluid. If aluminium is used for any housing or other component, it
shall be suitably coated and certified as copper free i.e. less than 0.4%
copper by mass.

6. Material for all junction boxes, and instrument electronics and termination
housings shall be SS 316.

7. All proposed vendor standard plastic components if any shall be non-toxic
and fire resistant, UV stabilized and compatible with the environmental
conditions.

8. All spindles, bushings, bolting, screws, brackets, etc., shall be manufactured
from a suitable grade of stainless steel as a minimum. All bolts and screws
shall have a flat 316 SS washer under the nut, and the thread length shall be
such that there is complete full engagement of the nut, with a minimum of two
threads protruding.

9. Stand pipes, supports for instruments and any other item directly welded to
the structure shall be CS galvanized.

10.All material for instrumentation, in contact with process fluid containing CO2 in
excess of 2 psi partial pressure, shall be as follows:

Fluid Temperature Material to be used
< 71oC ASTM A182-F316 (316SS)
> 71oC ASTM A182-F51 (2205 duplex steel)

11.Moulded polyester parts shall be anti-static for hazardous area locations, and
in general be constructed from UV-stabilized glass reinforced polyester.
Surface resistance shall not be less than 109 Ohms. Impact resistance to be -
25%.


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