Stainless Steel Tubing, Fittings, and Valves for Instrument Service 170 bar g (2500 psig) Maximum
- PURPOSE
1.1 This engineering standard defines the criteria for the selection of stainless steel tubing, fittings, and valves used for instrument service below 2500 psig.
- SCOPE
2.1 This standard applies to all field instrument packages, except instrumentation for ultra-high purity service.
2.2 This engineering standard shall be used for tubing in instrument service at pressures up to
170 bar g (2500 psig) and at temperatures from -30° to +150°C (-20° to + 300°F).
- RELATED DOCUMENTS
3.1 American Society for Testing and Materials (ASTM)
A182 Specification for Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High Temperature Service
A269 Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General
Services
A276 Specification for Stainless Steel Bars and Shapes
3.2 American Society of Mechanical Engineers (ASME)
B31.3 Process Piping
- MATERIAL SELECTION
4.1 Type 304/304L dual-certified stainless steel is the preferred material. Deviation from this standard applies only if another stainless steel type is required to match the process piping or is a customer request.
4.2 Type 316/316L dual-certified stainless steel may be used in lieu of Type 304L when required for increased corrosion resistance.
5. TUBING
5.1 Tubing sizes shall be as follows:
| • Process tubing
• Pneumatic signal tubing • Analyzer sample tubing • Instrument air supply tubing within 18 inches of user |
3/8″ OD
1/4″ OD, for response speed 1/4″ OD, for response speed 3/8″ OD |
Note: The project team will review customer requested deviations from this standard.
5.2 Design pressures have been calculated using ASME B31.3 allowable stress values and
ASTM A269 manufacturing tolerances.
5.3 Welded tubing shall be surfaced conditioned by the manufacturer to ensure compatibility with compression fittings.
5.4 Tubing shall be fully annealed, welded, Type 304/304L dual-certified stainless steel per
ASTM A269, hardness RB80 or less. Wall thickness shall be per Table 1.
| TABLE 1—STAINLESS STEEL TUBING WALL THICKNESS | |||
| OD (inches) | WALL (inches) | MAXIMUM PRESSURE
bar g psig |
|
| 1/8 | .028 | 170 | 2500 |
| 1/4 | .028 | 170 | 2500 |
| 3/8 | .035 | 170 | 2500 |
| 1/2 | .049 | 170 | 2500 |
- FITTINGS
6.1 Compression fittings shall be Swagelok® as manufactured by the Crawford Tube Fittings Co., Solon, Ohio, or Parker A-Lok® manufactured by Parker Hannifin Corp., Instrumentation Connectors Div., Huntsville, Alabama, and shall be Type 316 stainless steel made from forgings per ASTM A182 or bar stock per ASTM A276.
6.2 Compression fittings shall be supplied and used as complete assemblies.
6.3 Pipe fittings, such as nipples, couplings, reducers, and plugs, shall be hex-pattern, Type 316 stainless steel precision fittings shall be Cajon Brand, as manufactured by the Swagelok Company, or equivalent. Pipe fittings shall be assembled using Teflon pipe thread tape or oxygen compatible Teflon pipe dope on all connections.
6.4 Mixing of compression fittings materials (that is, brass and stainless steel) at a transition joint between copper and stainless steel tubing systems is prohibited. Transitions between tubing materials shall be accomplished by means of screwed fittings.
- VALVES
7.1 Shut-off valves shall be integral bonnet needle type forged Type 316 stainless steel, 206 bar g (3000 psig) at 40°C (100°F), with Type 316 stainless steel stem, PFA packing, and integral seat. Swagelok® connections as manufactured by the Whitey Company are the preferred connections. Threaded connections may be substituted when a Swagelok connection valve is not available.
7.2 Shut-off valves used in oxygen service shall be specified as oxygen cleaned and with a blue handle by adding the suffix “W1” and “BL” to the model number. (Example: SS-xxxx-W1-BL).
7.3 Shut-off valves used in critical service applications, as indicated on the flowsheet at the process block valve by LO (Lock Open) or LC (Lock Closed), shall be specified with an orange handle by adding the suffix “OG” to the model number. A Nupro brand “Valve Lokout®” accessory, manufactured by the Swagelok company, shall be installed around the handle and secured with a nylon cable tie to prevent accidental closing or opening of the valve.
7.4 Ball valves shall be specified with a maximum pressure of 17 bar g (250 psig), spring-loaded packing to reduce the frequency of packing adjustments and extend the working temperature range by adding a “T” to the model number (Example: SS-xxTxx.) The preferred ball valves shall be Whitey “40” series manufactured by the Swagelok company.
7.5 Manifold valves shall be soft seat needle type, forged 316 stainless steel, 206 bar g
(3000 psig) at 40°C (100°F), 316 stainless steel stem, TFE Chevron packing material, PPS- Polyphenylene Sulfide seat material. Connections shall be 1/2″ FNPT.