AU2006203701B2 - Method for installing an industrial piping system to resist corrosion - Google Patents

Abstract

Disclosed is a method of installing or repairing an industrial piping system to resist corrosion comprising: installing or repairing a plurality of pipe sections (60) of corrosible material 5 for conveying fluids involved in an industrial process; and installing an insulating system for said corrosible pipe sections. The insulation system is formed from a plurality of preformed insulation modules (10,20) including a cladding layer (18) and an insulation layer (14). The insulation layer (14,24) of a pre-formed insulation module (10,20) is spaced from an outer 10 surface (66) of a pipe section (60) by spacing means (26) leaving a gap (62) between insulation layer (14,24) and outer surface (66) of pipe sections (60) which results in a reduction of corrosion rate of pipe sections (60) to less than a predetermined rate. The method is especially adapted to reduce risk of stress corrosion cracking of pipes of austenitic steel due to excessive build up of 15 chloride ions at the pipe surface.

Description

Pool Section 29 Regulation 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Method for installing an industrial piping system to resist corrosion The following statement is a full description of this invention, including the best method of performing it known to us: 1 METHOD FOR INSTALLING AN INDUSTRIAL PIPING SYSTEM TO RESIST CORROSION This invention relates to a method of installing an industrial piping system. Industrial piping systems include those for use in the chemical and 5 petrochemical industries, among which are the oil refining, polymer and fertilizer industries. Such systems may be both complex and expensive. Further, as such systems may handle highly corrosive materials, especially under high temperature and pressure conditions, materials of construction for such systems are carefully selected having regard to process conditions. Such materials are 10 often relatively expensive and failure may cause significant environmental and safety hazard not to mention substantial expense of replacement. The piping system will, most commonly, be insulated. In the industrial context, the object of insulation of a component is to maintain a desired temperature within that component. Thus in a chemical plant,.tanks and pipes 15 may hold or carry materials such as solids, gases or liquids which must be maintained within controlled temperature limits for efficient use within the process being conducted within the chemical plant. Insulation affects the cost efficiency of the chemical plant as heating and cooling costs may be substantial and may be reduced by effective insulation to 20 prevent heat loss or gain from the insulated component. However, a significant problem, identified by Liss in "Preventing Corrosion Under Insulation" is the problem of pitting corrosion galvanic corrosion, alkaline acidic corrosion, and stress corrosion cracking which may occur under insulation such as polyurethane foam insulation. Since insulation tends to cover the surface 25 of a metallic pipe it allows corrosion to progress un-noticed until failure occurs. As insulation is a critical element of most industrial piping systems, a good deal of attention has been directed to the corrosion under insulation ("CUI") problem. Coating systems are commonly employed as a response to the corrosion problem. Coatings must be applied with care and require long service life, 30 possibly up to 10 to 15 years. Permeable or poorly applied coatings can allow corrosion to severely restrict the service life. It will be understood here that corrosion may be caused by conditions external to the process as much as by the 2 actual process conditions to which most attention is addressed when designing and constructing industrial plants. It is the object of the present invention to provide a method for installing an industrial piping system to resist corrosion which avoids the degree of corrosion 5 under insulation encountered with current installation techniques. With this object in view, the present invention provides a method of installing or repairing an industrial piping system to resist corrosion comprising: a) installing or repairing a plurality of pipe sections of corrosible material for conveying fluids involved in an industrial process; and 10 b) installing an insulating system for said corrosible pipe sections, said insulation system being formed from a plurality of preformed insulation modules including a cladding layer and an insulation layer, said insulation layer of a pre formed insulation module being spaced from an outer surface of a pipe section included in said plurality of pipe sections by spacing means leaving a gap, the 15 gap being disposed between insulation layer and outer surface of said pipe section to reduce corrosion rate of said pipe section to less than a predetermined rate. The gap may be filled with a gas, air for example. Otherwise, the gap is left vacant. By "predetermined rate" is meant a corrosion rate for the corrosible 20 material less than corrosion rate for a system in which the insulation layer is in direct contact with the outer surface of the pipe. Reduction of corrosion of metallic pipe sections is of primary importance. Such contact has been found, by the Applicant, to increase corrosion risk. Corrosion mechanisms that are addressed by the installation method of the present invention include galvanic 25 corrosion, pitting corrosion and general corrosion. The most relevant corrosive ion is chloride ion though corrosive action of other ions may be reduced in accordance with the invention. Stress corrosion cracking, especially of austenitic stainless steel is particularly associated with concentration of chlorides on metal surfaces at temperatures above about 600C. Techniques for measuring corrosion 30 rate are understood in the chemical engineering art. Corrosion rate is also affected by the material or materials forming the insulation layer. Water, liquid, vapour and gas retaining materials may cause higher corrosion rate. Insulation as a source of chlorides is associated with stress 3 corrosion as above described, particularly where such insulation is in direct contact with pipes increasing chloride concentration. If barrier layers or films are included within the insulation layer, corrosion rate may be reduced, though some barrier layers may retain liquids and gases causative of an increased rate of 5 corrosion. The spacing means should be made from a material that will not increase tendency to corrosion of pipe sections. The spacing means may be of any shape or configuration that will enable spacing of insulation layer from outer pipe surfaces to form a gap which may be of annular shape. The spacing means may 10 be made from rubber or plastics. However, the spacing means may also be made of metal, such as steel, provided that such metal does not create a galvanic couple with the pipe material that could cause an unacceptable corrosion rate. By an unacceptable rate of corrosion is to be understood a corrosion rate that will reduce the design service life of the pipe. The spacing means may be provided in 15 the form of rings or bands. These may extend wholly or partly around a circumference of a pipe section. The bands may be spaced at regular or irregular intervals along a pipe length. The method of the invention may be implemented when the industrial piping system is first installed. The method may also be implemented during 20 scheduled or other maintenance which, compendiously, is regarded as repair. The method may be supplemented with coating or painting of pipe sections with materials for resisting corrosion. Insulating material for inclusion in the insulation layer may include a fibrous material. Fibres may be synthetic or natural and man-made mineral fibres are 25 especially contemplated within the scope of the present invention. The fibres may be in rigid form. Alternatively, non-fibrous cellular materials such as polyurethane may be used as insulating material. The material may take any suitable rigid or flexible form, for example panels, mattresses or blankets. These fibres may be sealed, such sealing aimed at preventing fibre escape and possibly 30 also forming a moisture barrier layer that may assist in resisting corrosion. Suitable insulation materials for inclusion in the insulation layer may also be selected from insulation foams such as flexible and rigid polyurethane polyisocyanurate foams. Chloride containing foams are advantageously avoided.

4 Materials less susceptible to liquid, gas, vapour and moisture retention increasing corrosion rate are selected. Modules may be designed with insulation materials suitable for high temperature applications as might be encountered in chemical plants and oil and gas refineries and installations where high temperatures may 5 be required. High temperatures are regarded as those in excess of the boiling point of water. The cladding material may be formed from a metal such as stainless steel, coated steel or aluminium; or a polymeric material selected to resist corrosion. The cladding material could be a composite material. It should be resistant to 10 relevant environmental and plant conditions. Typically, the cladding material would be formed into a resilient part-cylindrical sheet that maintains some degree of resilience following fabrication into pre-formed modules. The cladding requires both temperature and corrosion resistance. It is directly adhered to the insulating layer by adhesives or other means. Possibly, any sealing agent for sealing 15 fibrous insulating material may be used as the adhesive agent. Water or other barrier, such as vapour barrier, layers or films may be included. Generally, the preformed insulation module is a part cylindrical module, such as a semi-cylindrical module. It advantageously includes connection means for connecting it to other modules during installation. By pre-formed is meant that 20 the insulation module may be manufactured, as a complete insulating article, prior to transfer to, and installation at, a factory site. The factory site may be very remote to the site where the manufacturing plant is located. Such pre-fabrication of modules, which may be installed directly at the site, saves significant site costs and reduces the cost of the insulation project. 25 A suitable pre-formed insulation module, for use in installation of the piping system, has a body shaped to a component to be insulated including: an unstriated insulation layer shaped to the body comprising a rigid fibrous insulating material having fibres sealed, having no specific orientation relative to the module, within said layer by a sealing agent and being substantially uniform in 30 composition and density over a cross section of said layer which has an inner surface adjacent to a surface of a component to be insulated; an outer surface and contacting surfaces; 5 a substantially non-fibrous resilient cladding layer shaped to the body and directly adhered to the insulation layer at the outer surface thereof; and connection means disposed along the length of the body for hingelessly connecting with at least one further adjacent insulation module wherein said 5 insulation and cladding layers of said module are disposed relative to each other such that, on connection to said further insulation module, insulation layers of said module and said at least one further module are brought into contact along said contacting surfaces of the insulation layers of the modules for insulating at least a portion of the component. Modules of this type may incorporate the 10 spacing means. The method of installation or repair of an industrial piping system of the present invention present cost and safety advantages, in terms of reduced corrosion under insulation, over systems and methods currently employed. The various aspects of the invention may be more completely understood 15 from the following description of preferred embodiments thereof made with reference to the accompanying drawings in which: Figure la is a side sectional view of a pre-formed module suitable for insulation of a length of pipe in accordance with one embodiment of the method of installation of the industrial piping system of the present invention; 20 Figure lb is an exploded view of two pre-formed modules of the kind shown in Figure 1a showing the assembly; Figure 2 is a perspective view of two pre-formed modules fitted together to insulate a pipe section (not shown) in accordance with the method of installation of the industrial piping system of the invention; and 25 Figure 3 is a front sectional view of the module assembly as shown in Figures 1b and 2 insulating a pipe section in accordance with the method of installation of the industrial piping system of the invention; and Figure 4 is a cross-sectional view of the module assembly of Figure 3. For purposes of example, the installation method of the invention will be 30 described with reference to a chemical plant, such as an oil refinery, in which fluids at high temperature and pressure are conveyed by piping systems throughout the plant. Various flowsheets for oil refinery plant are publicly available. It will also be understood that the construction of such plants is within 6 the knowledge of those skilled in the art of process engineering and construction. Therefore, detailed description of oil refinery plant flowsheets is omitted. During construction of such plants, it is necessary to install piping systems formed of a plurality of pipe sections for conveying process fluids from one unit 5 operation of the refinery to another unit operation. Such pipe sections or pipes are selected and installed in a conventional manner. A similar process may be followed if repair of plant piping is required whether during scheduled maintenance or otherwise. At an appropriate point of construction, an insulating system for pipe 10 sections must also be installed. A preferred insulation system is formed from a plurality of preformed insulation modules. Referring now to Figure 1, there is shown an insulation module 10 suitable for use in the installing of the insulating system. The module 10 is of semi cylindrical shape suitable for use in the partial insulation of a pipe, partial because 15 the step of insulation module will need to co-operate with further modules to completely insulate the pipe. Modules may be designed which allow insulation by a single module of hinged or analogous construction. The module 10 has an insulation layer 14 and a cladding layer 18. Insulation layer 14 should typically be selected to be less susceptible to retention 20 of moisture, gases, vapours or liquids that may cause corrosion of pipes. The material may be fibrous. The fibres making up a fibrous insulation material may be natural or synthetic, typically mineral, fibres such as fibreglass. It is such materials that have posed safety difficulties in on-site manufacture and installation in the plant. Cellular materials may also be employed, for example rigid cellular 25 polyurethane foams as manufactured and supplied by the Applicant. Such materials may advantageously take the place of fibrous materials as described. Fibreglass to form insulation layer 14 may be sprayed with acrylic emulsions, for example as described above, or other suitable sealing agent to seal the insulating material. Sealing prevents escape of substantial quantities of 30 fibres and unsatisfactory levels of such fibres in the insulation environment. It may also form a moisture barrier that assists in resistance to corrosion. The cladding material to form cladding layer 18 is metallic in nature, say of stainless steel, coated steel or aluminium. Polymeric or composite materials could also be 7 used. In other words, the cladding material should be resistant to plant conditions, particularly corrosion and temperature resistance and noting corrosion risk crated by moisture. The cladding material may be painted with a corrosion resisting paint. Inner surface 14c of insulation layer 14 is intended to face the 5 outer surface of a pipe section to be insulated, being spaced therefrom by a spacing band to form a gap as described further below. A module 20 may be connected to module 10 for insulation of a pipe section within the piping system. Of similar construction to module 10, the module 20 includes an insulation layer 24 with an inner surface 24c. 10 Other constructional details of modules 10 and 20, as well as methods of connection of these, are described in the Applicant's US Patent No. 6921564, the contents of which are hereby incorporated by reference. The insulation modules 10 and 20 may be formed in lengths or customised to the various pipe sections in the plant as well as to pipe fittings such as bends 15 and elbows. The installation method for a piping system constructed of austenitic stainless steel, proceeds as follows. The lengths of cylindrical pipe sections for the system are determined and installed in conventional manner. The insulating modules of the same kind as modules 10 and 20 described above are 20 manufactured to allow insulation of the pipe sections. For a pipe section 60, two semi-cylindrical modules are required as exemplified, in assembly, in Figure 2. A greater number of modules could be used where pipe diameter suggests that modules of lesser circumferential extent than semi-cylindrical are more conveniently to be installed on the pipe. Spacing bands 26, of circular cross 25 section, are then arranged along the pipe section 60, these bands being a corrosion resistant material perhaps of steel or stainless steel but of a material selected to minimise galvanic corrosion rate. The bands 26 may be continuous. Bands 26 could be spaced along pipe sections prior to installation. They may be fitted at any time prior to the insulating step or formed by co-operation of 30 complementary spacing members formed in modules 10 and 20 respectively. Spacing of bands 26 may be at regular intervals of dimension B as shown in Figure 3. Irregular spacing of bands 26 is also possible.

8 One module 20 is then press fitted over the spacing bands 26 and the pipe section 60 leaving an annular gap 62 between the inner surface 24c of the insulation layer 24 and the outer surface 66 of pipe 60 as conveniently shown in Figures 3 and 4. 5 The other module 10 is likewise fitted over the spacing bands 26 and the pipe section 60 leaving an annular gap 62 between the inner surface 24c of the insulation layer 24 and the outer surface 66 of pipe 60 also as shown in Figures 3 and 4. The overlapping portions 18a of the cladding layer 18 fitting over the surface of the first module 20 to connect the modules 10, 20 together on 10 interference fitting of bead 16 within channel 26. Insulation layers 14, 24 of adjoining modules 10, 20 contact along their contacting surfaces 14ba. Welding or riveting or other fastening is employed to complete the job. This is especially done at the circumferential beads though could also be done along the longitudinal beads 126. Water-tight sealing is advantageous in resisting 15 corrosion. This may be achieved with water-proof tape and/or sealants such as silicone sealants. The annular gap 62, being filled with air, forms an air barrier between inner surface 24c of insulation layer 24 and pipe section outer surface 66 which prevents corrosive chlorides or other corrosive ions from the insulation coming in 20 contact with the pipe section outer surface 66, a build up to certain concentrations of such ions being associated with stress corrosion cracking of austenitic stainless steel at temperatures above 600C. Oil refinery operations may involve fluids having significantly higher temperature than this. The dimensions of spacing bands 26 are selected to leave an annular gap 25 62 of sufficient width to reduce corrosion rate as determined by testing or empirically. Larger bands may leave larger gaps 26 but insulation cost may increase. Accordingly, the corrosion rate of pipe section 60 will be reduced to a rate less than that for a system in which the insulation layer 14 is in direct contact with pipe section outer surface 66 as with prior art insulation methods. 30 Methodology for measuring the corrosion rate is described at Perry's Chemical Engineering Handbook, Eleventh Edition, pages 28-10 to 28-12 and 28-24 to 28 27 of which are hereby incorporated by reference. Acceptable corrosion rates may be set by reference to the desired service life of pipes within a piping system.

9 Use of two modules is unlikely to insulate an entire pipe, other like modules are probably to be employed. In this case, adjacent modules must co operate and be connected together to properly insulate the pipe while leaving annular gap 62 along the pipe length between insulation layer surface 14c and 5 pipe surface 66. As has been described above, connection portions of modules 10 and 20 are overlapped with the end portions of an adjacent module and with each other suitably securing adjacent modules together to create a water seal particularly when supplemented by use of welding, rivetting and/or use of sealants and a substantially continuous and complete insulation layer along the 10 length of pipe. Water sealing also has an important role in resisting corrosion since moisture ingress may be a significant cause of corrosion. This process proceeds until the entire piping system is insulated. Modifications and variations may be made to the method of installation or repair of a piping system in accordance with the present invention or 15 consideration of the disclosure by the skilled reader of this disclosure. Such modifications and variations are considered to fall within the scope of the present invention. For example, the materials of construction of the pipe sections need not be of austenitic stainless steel. Spacing means may have other material properties which assist in reducing corrosion in the particular plant environment of 20 interest.

Claims (11)

1. A method of installing or repairing an industrial piping system to resist corrosion comprising: installing or repairing a plurality of pipe sections of corrosible material for 5 conveying fluids involved in an industrial process; and installing an insulating system for said corrosible pipe sections, said insulation system being formed from a plurality of preformed insulation modules including a cladding layer and an insulation layer, said insulation layer of a pre formed insulation module being spaced from an outer surface of a pipe section 10 included in said plurality of pipe sections by spacing means leaving a gap, the gap being disposed between insulation layer and outer surface of said pipe section to reduce corrosion rate of said pipe section to less than a predetermined rate.

2. The method of claim 1 wherein said gap is filled with a gas. 15

3. The method of claim 2 wherein said gas is air.

4. The method of any one of claims 1 to 3 wherein said spacing means is a ring.

5. The method of any one of claims 1 to 4 wherein spacing means are spaced at regular intervals along a length of a pipe section. 20

6. The method of any one of claims 1 to 5 wherein stress corrosion cracking is avoided by lack of contacting of insulation layer with pipe section following installation.

7. The method of claim 6 wherein said insulation layer is treated with a sealing agent to form a moisture barrier layer. 11

8. The method of any one of claims 1 to 7 wherein a dimension of said spacing means is selected to leave a gap of sufficient width to maintain corrosion rate less than a predetermined rate.

9. The method of claim 8 wherein build up of chloride concentrations is 5 reduced by spacing the insulation layer from the pipe section outer surface.

10. A pre-formed insulation module, when used in installation of the piping system according to the method of any one of the preceding claims comprising a body shaped to a component to be insulated including: an unstriated insulation layer shaped to the body comprising a rigid fibrous 10 insulating material having fibres sealed, having no specific orientation relative to the module, within said layer by a sealing agent and being substantially uniform in composition and density over a cross section of said layer which has an inner surface adjacent to a surface of a component to be insulated; an outer surface and contacting surfaces; 15 a substantially non-fibrous resilient cladding layer shaped to the body and directly adhered to the insulation layer at the outer surface thereof; and connection means disposed along the length of the body for hingelessly connecting with at least one further adjacent insulation module wherein said insulation and cladding layers of said module are disposed relative to each other 20 such that, on connection to said further insulation module, insulation layers of said module and said at least one further module are brought into contact along said contacting surfaces of the insulation layers of the modules for insulating at least a portion of the component. 12

11. A method of installing or repairing a piping system substantially as herein described with reference to the drawings. 5 DATED this 25th day of August 2006 KAEFER INTEGRATED SERVICES PTY LTD WATERMARK PATENT & TRADE MARK ATTORNEYS 290 BURWOOD ROAD 10 HAWTHORN VIC 3122 AUSTRALIA P26032AU00