Thin Wall Stainless Steel (TWSS) Piping and Fittings for Glycol and Water Duties

Transcription

1 Thin Wall Stainless Steel (TWSS) Piping and Fittings for Glycol and Water Duties 1.0 Introduction The purpose of this standard is to bring together the information relative to design, manufacture and installation of glycol and water thin wall stainless steel (TWSS) pipework on selected Star equipment including vent lines, glycol and water lines, cooler drain lines and condenser drain lines. In general the use of TWSS pipes can be considered for long glycol and water pipe runs. Pipe runs should change to heavier wall carbon steel within 5 metres of pumps or other vibrating equipment. On contracts where an application standard is specified by a client or by an inspecting authority (on a client s behalf) then that standard will take precedence over the Star standard. Pressure testing on TWSS piping shall be carried out in accordance with Star Standard Specifications No s 113 and 125. For TWSS applications on glycol and water, design engineers should consider ordering air coolers with stainless steel terminations. s always we will expect welding to procedures approved by Star Production Department and with 10% NDT. 1.1 Pipe Specification Unless otherwise specified the TWSS shall be Grade 304L or 316L. The TWSS can be specified as DIN (often referred to as nominal bore or metric bore thin wall stainless steel tube). The tables of dimensions and weights shown in Table 1 are taken from the Stainless Steel Metric Stock (SMS) Limited brochure for the SMS 100 range of metric bore TWSS pipe. Where we are calling for the pipe and refer to the metric bore dimension we should always clearly state our required wall thickness as shown in Table 1. Outside Diameter Inside Diameter Wall Thickness Weight kg/m Table 1 Metric Bore TWSS L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 1 of 8

2 TWSS is also available as STM 312 material. In this case the pipe should be ordered against the pipe outside diameter with schedule 5 wall thicknesses. Size for size the 312 schedule 5 pipe wall thicknesses are thicker and weights per metre run are greater than those for the metric bore pipe. Table 2 gives dimensions and weights. Outside Diameter Inside Diameter Wall Thickness Weight kg/m Table 2 STM 312 TWSS Both 304L and 316L offer good resistance to corrosion and contamination and both have excellent weldability. Our preference will be to use 304L (which tends to be cheaper) unless the material is likely to come into contact with chlorine or softened water in which case we should use 316L The pipework OD should be clearly shown on our Diagram of Connections. This will allow the insulation contractor to select the correct diameter of insulation Screwed pipework and fittings may be used for water, brine and glycol pipework with design pressures up to 8 Bar G Short radius 90 elbows, equal tees, reducing tees and end caps may only be available in 316L The Mapress pipework system may only be used for drains ll pipe purchased for Star installations and packaged units will be internally and externally clean. 1.2 Pipework Design General rrangement ll pipework between anchors or other restraint points shall be arranged and supported to allow normal movement due to expansion and contraction without the need for expansion joints. ll connections are to be made to headers and equipment using formed fittings, except as below: L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 2 of 8

3 1.2.2 Stab-ins Stab-ins will be allowed according to the following table and notes provided the branch size is 25NB or above. The designs include a 10% allowance to cover system pressure tests at 1.1 times the allowable pressure and a further safety factor of at least 10%. OD Header Wall Maximum branch size for 8 Bar(G) allowable pressure on glycol and water OD Wall Table 3 Maximum allowable stab in sizes Notes: (1) No two pipe branches will be within 3 diameters of the largest branch from each other along the axis of the header pipe and no branch will be within 100 of any other weld except the longitudinal pipe weld. (2) ll branches will be perpendicular to the header and on the centre line Pipe Closures Welded dished end caps shall be used for closures at ends of all pipework. Flat closures are not allowed Pipe Support Spans Support spans to be based on spans required in Star SS 69 Support Span for Refrigeration Pipework. 1.3 Butt Weld Pipe Fittings The material specification for stainless steel butt welded pipe fittings, bends, tees, reducers and caps used in Star installations and units will be STM 403, WP304L or WP316L unless specified otherwise and will be ordered to suit the pipe outside diameter. Note: Where the end of a pressure carrying pipe is to be sealed, a standard butt weld dished end cap shall be used. L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 3 of 8

4 1.3.1 The dimensions of all stainless steel butt weld fittings will conform to DIN short radius bends, DIN 2643 reducer, reducing tees and end caps, DIN 2559 equal tee. For all pipe work from 15NB to 250NB the wall thickness of fittings will be specified as follows: 15NB 40NB 50NB 250NB Wall thickness 1.5 (minimum) Wall thickness 2.0 (minimum) 1.4 Flanges ll flanges will consist of a stainless steel pressed collar and an electro zinc plated backing flange to BSEN Type ND16/3 (PN16) for pipe sizes from 32 NB up to 150 NB and BSEN Type ND10/3 (PN10) for pipe sizes for 200 and 250 NB. 1.5 Paint Specification Prior to applying polystyrene or polyurethane or PIR (Nilflam) insulation the pipe is to be cleaned of any oil or grease and two coats of antichloride barrier paint will be applied. (Kingspan KP14X or Roster tlas 53-73). Refer to Insulation Subcontract Purchase Specification SF Insulated Pipe Supports The insulation for the supports will be as detailed in SS36 Insulation and Vapour Sealing of Refrigerated Pipes and Vessels. 2.0 Screwed Joints and Compression Fittings 2.1 Screw Thread Joints Screw thread joints may be used in conjunction with stud couplings, gauge and instrument valves and pipework up to and including 25 bore. In general, the screw thread will be NSI B NPT Weld preps are required when butt welding screwed pipe onto metric bore TWSS. Pipe size suitable for screwing are as follows: ½ NPT - Pipe size 21.3 OD x 2.8 ¾ NPT - Pipe size 26.7 OD x NPT - Pipe size 33.4 OD x 3.4 L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 4 of 8

5 Note, the weld preparation shown above should be taken as typical only the preparation must be made to suit the actual weld procedure being used Typical limits for bore difference and alignment using TIG welding with a root gap: Over NB Up to and Including NB BS2971 Bore Difference BS2971 lignment L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 5 of 8

6 3.0 Valves 3.1 Isolation Valves The termination format for different valve sizes is given in Table 4. The use of ball valves (3 piece) for sizes up to and including 40 NB has been assumed. For sizes 50 NB and above the use of butterfly valves has been assumed. OD Pipe Size ID 3.2 Other Valves Valve Size Termination Format Weld and Flange Type Pressure Rating Bar G Screwed or Screwed or Collar and Backing 8 BSEN PN16 Flange Screwed or Screwed or Collar and Backing 8 BSEN PN16 Flange Screwed or Screwed or Collar and Backing 8 BSEN PN16 Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN16 Collar and Backing Flange BSEN PN10 Collar and Backing Flange BSEN PN10 Collar and Backing Flange 8 Table 4 Valve Terminations When valves other than those covered in section 3.1 are used, the matching of the bore of the valve or the mating flange must be checked to ensure that the bore variation is in line with the application. L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 6 of 8

7 4.0 Installation Standards, Welding Standards, Welding Processes and Inspection 4.1 Installation Standards The application standards for all pipe work on Star installations and package units is dependent on the system design and will be as follows: System Design Pressure Up to and including 8 bar pplication Standard BS Class II Category. TIG welding (with rgon Purge unless otherwise approved by Star) of stainless steel pipework for carrying fluids 4.2 Welding Standards ll welding on pressure carrying pipework on Star installations and package units will be carried out to verified procedures to BS ENIS : Specification and approval of welding processes for metallic materials. The procedures will cover the range and type of welds required for the pipework being welded ll welders working on pressure carrying pipework on Star installations and units will have current verified approval to BS EN287, Pt 1: pproval testing of welders for fusion welding. The approvals will cover the range and type of welds required for the pipework being welded Other national welding standards such as SME VIII may be accepted, provided welding procedures and current qualifications of the welders cover the range and type of welds required for pipework being welded. Where it is proposed that an alternative standard is used, this should be cleared with the Technical Department and the accredited inspection authority where appropriate. 4.3 Welding Processes ll butt welded joints will be welded using tungsten inert gas arc welding (TIG) with rgon Purge Oxyacetylene welding is not allowed Welds on pipe that is not intended to be insulated shall be cleaned with a clean stainless steel wire brush to leave a bright finish (as bright as the parent material). L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 7 of 8

8 4.4 Inspection Requirements The requirements in this section are the minimum to be used on Star installations and packaged units. The requirements apply to all welded pipe including relief valve vent pipework, glycol and water piping, including cooler and condenser drains Visual inspection of all pipework welds to ensure conformity with the requirements of the application standard being used Non destructive inspection of butt welds will be carried out. The percentage of welds subjected to non destructive inspection will be as follows: pplication Standard BS2971: % of each welder s production of butt welds Radiographic inspection to BS2910 will be used for butt welds Defect limitation and any rectification work required will be in accordance with the application standard being used for the inspected pipework ll non destructive inspection will be carried out to approved procedures (written by a PCN level 3 qualified NDT expert) and the interpretation of the inspection report will be by qualified personnel Records weld identification record will be created each time a non destructive inspection is carried out. The record will have the following information: 1. Star order number and job number 2. pplication standard to be used for interpretation of NDT results 3. Weld identification reference 4. Weld location this may require a location sketch. 5. Welder s identification reference ll non destructive test records and radiographs will record: 1. Date 2. Job number 3. Weld identification reference 4. Welder identification reference The weld identification record and the non destructive inspection records will be filed together and kept with the main job file in Thornliebank or kept with the package unit records by the Works Office (for industrial contracts) or kept by the Branch Manager (for branch contracts). Date Revision Change Originator Sept First Draft G May 2005 B First Issue G/DJH L:\Standard Specifications\SS.150.B.Thin Wall SS (TWSS) Piping & Fittings for Glycol & Water Duties.doc Page 8 of 8