1. PURPOSE
1.1 This engineering standard defines requirements for the design of perlite insulated cold boxes, cold cans, and crossover ducts. For the purpose of this document, the term cold box means cold box, cold can, or crossover duct.
1.2 These requirements are given primarily to maintain the integrity of the cold box piping, equipment, and structure.
2. scope
2.1 This engineering standard applies to all perlite insulated cold boxes, cold cans, and crossover ducts. There are additional requirements for cold boxes that contain a brazed aluminum heat exchanger in oxygen service operating above the limits defined in 2S301. Additional requirements for insulating brazed aluminum exchangers in a pumped liquid oxygen (LOX) cycle air separation unit (ASU) are given in 3CB00002.
3. related documents
3.1 Air Products Engineering Documents 2S301 Use of Aluminum in Oxygen Service 3CB00005 Perlite Loading 3CB10402 Cold Box Valve Cages 3CB10403 Mineral Wool/Perlite Partition Design 3CB00002 Cold Box Design Criteria for Pumped LOX or LOX Boil Cycle Heat Exchangers To be published at a later date.
4. Definitions and abbreviations
4.1 Mechanical joint: A joint in a piping system in which the pressure seal is effected by close fitting mating surfaces held in compression by mechanical means. Included are flanged joints, screwed joints, and compression-type joints. Bimetallic transition joints are not included.
4.2 Ratcheting failure: A mode of failure that occurs in cyclic service in which a component yields during part of the cycle, but is not “yielded back” in the balance of the cycle. The component continues to yield on successive cycles.
4.3 DN: Nominal diameter; used as a prefix with nominal pipe sizes expressed in millimeters.
4.4 NPS: Nominal pipe size; used as a suffix with nominal pipe sizes expressed in inches.
6. BACKGROUND
5.1 Refer to the Knowledge Library associated with this engineering standard for background information
6. General Requirements
6.1 Mechanical joints in perlite, with the exception of those specified in section 7.3, are strictly prohibited. All piping connections shall be welded or brazed. Mechanical joints, when required, shall be located in areas of the cold box insulated with mineral wool and shall be accessible from the outside of the cold box, preferably through a removable panel. Examples of items that shall not be located in perlite are: flanged valves, orifice flanges, valve bonnets, compression-type fittings such as Swagelok fittings, flanged or screwed adsorber fill and drain ports, and any other flanged or screwed connections.
6.2 Types of equipment without a proven history of reliable service shall not be perlite insulated unless project-specific written approval is obtained from the department manager responsible for cold box engineering.
6.3 Cold boxes or parts of cold boxes containing reversing heat exchangers shall be insulated with mineral wool.
6.4 To avoid the need to remove all of the perlite, parts of the cold box where entry is likely for repair or maintenance shall be partitioned from the rest of the box.
6.5 Crossovers between cold boxes may be insulated with mineral wool or perlite. Barriers shall be provided to prevent insulation migration between areas in the event that insulation is removed from one of the areas. Where barriers are utilised, provision shall be made to ensure that each section is adequately purged.
6.6 The cold box shall be made to accommodate some settling of perlite without exposing any cold piping or equipment. A minimum coverage of 450 mm (18 in) of perlite over the top of the highest cold pipe must be maintained. This can be achieved through increased box height or multiple fill ports (see paragraph 10.1) taking into account the angle of repose of the material.
7. Piping—general requirements
7.1 Piping shall be designed with full consideration of the loading imposed by perlite as described in 3CB00005.
7.2 Components with mechanical connections shall be grouped together as much as possible to minimize the number of areas in which mineral wool is required. Access shall be provided to all mechanical connections.
7.3 The use of expansion joints in perlite shall be avoided if at all possible. If it is not possible to avoid the use of expansion joints in perlite, then use of rockwool cages is strongly prefered. If it is deemed not possible to use a rockwool cage, then the following design considerations must be followed: Use of flanged expansion joints in perlited cold boxes shall be avoided. If their use cannot be avoided, approval of the Cold Box Engineering Manager is required AND flanges must be wrapped in three layers of 25 mm (1 in) thick rockwool balnkets with suffecient overlap. Center lugs on the tie rods must be used to reduce excessive movements caused by perlite loadings. Appropriately designed covers to protect bellows from perlite loading shall be used. Design features of an appropriately designed cover must include:- It must protect bellows from perlite loading.- It must prevent perlite particles from entering the convolutions and therefore restricting expansion joint’s designed movements.- It must not alter Expansion Joints designed stiffness’ nor restrict its movements.
7.4 The use of spring pipe supports in perlite is strictly prohibited. Because of the complex perlite loading condition (varying magnitude and direction), it is nearly impossible to design a spring pipe support that will operate correctly in all loading situations throughout the life of the cold box.
7.5 Cold box purge inlets and outlets shall be protected from perlite ingress.
7.6 Seal welding of threaded connections is unacceptable. In the event that a vessel or component with screwed connections is to be placed in service in perlite, the threaded end of the pipe or nozzle shall be cut off and the connection shall be made by welding (socket weld or butt weld).
7.7 Process piping, instrument lines, and conduit shall be routed in such a manner that minimizes penetrations through insulation barriers.
8. piping—material requirements
8.1 Aluminum
8.1.1 Background – refer the Knowledge Library associated with this Engineering Standard.
8.1.2 All aluminum lines DN20 (3/4 inch NPS) and smaller shall be Schedule 40 or heavier pipe. Larger sizes shall be Schedule 10S or heavier pipe.
8.1.3 The use of aluminum socket weld fittings shall be kept to a minimum.
8.1.4 DN 8 (1/4 inch NPS) aluminum pipe shall be supplied in coils and shall be installed in one continuous length. Joints (other than those at the ends) should be avoided. They are allowed only when they cannot be avoided, if both of the following conditions are satisfied: The joint is located in a vertical run. Pipe supports are located on both sides of the joint, such that bending stresses are minimized.
8.2 Stainless Steel
8.2.1 There are no restrictions specific to the use of stainless steel pipe or tube.
8.3 Copper
8.3.1 When used in horizontal runs through perlite, copper tube is likely to require more pipe supports than the same size aluminum or stainless pipe. For this reason, copper shall generally not be used in perlite. Exceptions to this are:
8.3.1.1 Copper tube may be used in vertical piping runs.
8.3.1.2 Copper tube may be used throughout a perlite insulated cold box provided that all of the following conditions are satisfied: The tube is type K, or the nominal wall thickness is at least 1.65 mm (0.065 in). There is a clearly demonstrated economic advantage over other materials. Project-specific written approval is obtained from the department manager responsible for cold box engineering.
8.4 Carbon Steel
8.4.1 Carbon steel may be used for purge vent lines and for purge supply and distribution headers.
9. Structural—general requirements
9.1 The cold box frame, panels, equipment supports, and pipe supports shall be designed with full consideration of the loading imposed by perlite described in 3CB00005.
10. Perlite fill and drain ports
10.1 On cold boxes, perlite fill/drain points shall be located on the roof as well as on platforms every 10 to 12 m (32 to 40 ft). The entry into the box shall be clear of obstruction by equipment or piping. The number, design, and location of fill points located on the face and roof of the cold box shall be such that all cold piping and equipment can be covered (as specified in paragraph 6.6) when perlite is poured through the points.
10.1.1 Perlite shall be filled up to an elevation 500 mm (19.7 in) below the first access point ensuring that the insulation void on the side furthest from the access point is also filled. Repeat this procedure for all remaining access points, then move to the access point(s) on the roof and fill with perlite as specified in paragraph 6.6.
10.1.2 The retrieval of perlite from the cold boxes shall be done through the fill points in the reverse order of filling. Gravity draining shall be used as much as possible.
11. Valve cages and insulation barriers
11.1 Mineral wool cages and other insulation barriers (partitions to prevent the flow of perlite from one area to another) shall be designed with full consideration of the loading imposed by perlite described in 3CB00005.
11.2 Penetrations through insulation barriers shall be sealed to prevent flow of perlite through the barrier.