a) Fixing fasteners – When fixing Inox CSSP to walls or other surfaces use Clips, holderbats or saddles, of stainless steel or plastic (UV stabilized for outside use), unless the pipe is sleeved in which case any appropriate materials can be used.
b) Fixing distances (spacing) – Horizontal runs shall be supported at a minimum of 30 cm to 50 cm intervals, vertical runs should be supported at a minimum of 50 cm to 60 cm, all fixed to the structure.
c) Fixing at valves and terminal fittings – Fix on both sides of valve or fittings within a maximum distance of 5 cm, and on formed bends within 5 cm of each side of the bend. Terminal fittings shall be securely fixed to the structure using wall plates before connecting the pipe.
When using INOX CSSPs in underground application or within walls, the following protection methods are recommended:
- PVC coating – some version of INOX CSSP are provided with PVC coating, these pipes are suitable for use underground and in walls.
- Zinc-rich epoxy primer – applying zinc-rich epoxy coating directly onto the stainless steel surface will create sufficient protection for the pipe to be installed in the above environments.
- Thermally sprayed aluminium (TSA) – applying TSA coating directly onto the stainless steel surface will create sufficient protection for the pipe to be installed in the above environments.
Important Note: although stainless steel provide good corrosion resistance under most conditions, in certain environments, such as certain soil types or when underground electrical current is present, corrosion processes may be accelerated and therefore additional protection is necessary.
The following are some additional steps that can help in reducing the risk of corrosion:
- Pack soil uniformly, as variable compaction can induce differential aeration effects. Stainless steels generally retain their passive film provided there is at least a few ppb of oxygen, i.e. 1000 times less than the concentration in water exposed to air.
- Avoid organic materials in the fill around buried stainless steel pipe, as they can encourage microbial attack.
- Avoid carbon-containing ash in the soils as it can promote localised galvanic attack on stainless steel.
- Oxygen access is critical; this can be done with the aid of good drainage and sand backfill.
- Avoid a sand-filled trench dug through clay, as it may become a drain which can exacerbate corrosion.
- The general guidelines for immersed service are that in neutral environments at ambient temperatures and without crevices, 304/304L may be used up to chloride levels of 200ppm, 316/316L up to about 1000ppm chloride and duplex (2205) up to 3600ppm chloride. The super duplex alloys (PRE>40) and the 6% molydenum super austenitic stainless steels are resistant to seawater levels of chloride, i.e. approximately 20,000ppm.
- Stray currents. All buried metals, including stainless steels, are at risk if there are stray currents from electrically driven transport, incorrectly installed or operated cathodic protection systems, or earthing faults in switchboards. Stray current corrosion can be identified as it causes localised general loss rather than pitting. It is also very rapid.