1. PURPOSE
1.1 This engineering specification defines the minimum requirements for the design and installation of temperature elements and conduit runs for cold boxes and site-fabricated cold column cans.
2. SCOPE
2.1 This specification applies to all cold boxes and cans designed and built for Air Products.
2.2 It covers the location requirement of the temperature element, installation, subsequent wiring, and wiring support installation within a cold box or cold can.
2.3 In the event of conflict between this specification and the project drawings, the project drawings shall have precedence.
3. related documents
3.1 Air Products Engineering Documents None
3.2 British Standards Institute (BSI) BS 4568 Steel Conduit and Fittings with Metric Threads of ISO Form for Electrical Installations
4. DEFINITIONS
4.1 Cold box: Vessels and equipment completely enclosed and supported off a rectangular section box structure, consisting of a steel framework totally clad in sheet steel.
4.2 Cold can: Sheet steel cylinders joined end-to-end with sheet steel top and bottom to enclose a self-contained, self-supporting column assembly. All piping is also supported from the column assembly.
5. TRANSITION WIRING
5.1 The temperature element assembly will be as detailed on the project instrument data sheets.
5.2 All elements (both parts of duplex) shall be wired back to a multiway junction box mounted off the external face of the cold box/can. Each wire and core shall be identified with cable sleeve markers, at both element and junction box ends, with the identification numbers specified in the connection schedule. Each pull box/condulet shall have wired-on tags stamped with the identity of the wires passing through it. When the multiway junction box is removed for shipping and the cables are coiled at the cold box face, special care is required to ensure that the wires are adequately numbered. This is to permit correct reconnection on site. In these cases each cable and wire shall be marked with the appropriate identification number using proprietary cable sleeve markers that are secure and cannot fall off in transit. The use of tape and indelible pen as a cable marking system is not acceptable. A further set of cable sleeve markers shall be supplied loose with the junction box for reconnection on site.
5.3 Sufficient wire shall be coiled in the element head to enable the element to be completely withdrawn for maintenance or possible future replacement.
5.3.1 Care shall be taken to ensure the cable insulation is not damaged when the cap is fitted to the element.
5.3.2 The terminals inside the element are not designed for large forces, so care shall be exercised when installing the cable tails.
5.4 Preferred element transition wire is Teflon insulated with Mylar Screen and Teflon served overall. Kapton as a substitute to Teflon is acceptable when approved in writing by Air Products on a case-by-case basis.
5.5 Care shall be taken when preparing the ends of the insulated wire tails to ensure that the conductors have been completely cleaned to bare metal where they are required to connect into terminal blocks. Cable shields at the element head end when using nongrounded trip elements shall be insulated by folding the shield back along the cable before the cable end is sleeved with Teflon sleeving. This is done to prevent any accidental earthing contact between the shield and any metal part of the assembly.
5.6 Care shall be taken when pulling the cable through the conduit that the cable insulation is not damaged by excessive force.
5.7 Crimp pins shall be used on stranded conductors. They shall not be used on solid conductors. Cable joins are not permitted between the element head and the junction box on the external cold box/can face.
6. LOCATION AND PROTECTION
6.1 Protection of the installation from mechanical damage, particularly while the cold box/can is being packed, is essential.
6.1.1 Whenever possible, the wells shall be located on the underside of the parent pipe.
6.1.2 Wells shall not be located in vertical lines, except when unavoidable, in which case protection shall be provided during packing operations.
6.2 Cold box elements shall be located for ease of access and, when possible, they shall be located near the cold box removable panels and valve maintenance covers. Isometric piping drawings or the CAD model shall be reviewed by the instrument designer to ensure elements are as close to valves in the same line where possible.
6.2.1 When direct access to an element is not possible, the element shall be located where the parent pipe runs closest to the cold box wall and where support for the conduit is available.
6.3 Cold can elements shall be located in the column wall, with a fabricated aluminium sheet protection cover, if required, to protect the element head when the cold can is being filled with perlite. For ease of access, manways shall, when possible, be located in the cold can wall near element locations. Isometric piping drawings on the CAD model or vessel assembly drawings shall be reviewed by the instrument designer to ensure elements are accessible.
6.3.1 When direct access to the element is not possible, the elements shall be located near to where piping transition penetrates the cold can wall, and where support for conduit is available.
6.4 When temperature elements are being installed in a hydrogen (H2)-purged cold box/can, a 3 mm diameter hole shall be drilled into the removable part of the temperature element connection head before installation. This is to allow for purge gas and any trapped air to escape from the conduit system (see paragraph 7.10).
7. CONDUIT GENERAL
7.1 Materials may be selected from either of the tables shown on the installation drawing (that is, metric or imperial depending on local availability).
7.2 The element head shall be connected to rigid steel conduit by a minimum length of flexible conduit approximately 300 to 450 mm (12 to 18 in), to be consistent with expansion requirements.
7.3 Conduit description for cold boxes: Flexible conduit shall be a covered stainless steel flexible core “Liquatite” type, suitable for high temperature service.
7.3.1 Fittings: Flexible conduit fittings shall be stainless steel, and be of propriety type, with one end male thread and the other suitable for connection to conduit described in paragraph 7.3.
7.3.2 The rigid conduit run within the cold box shall be either of a heavy-gauge welded-steel construction with a galvanised finish suitable for thread cutting to BS 4568 or, electrical metallic tubing (EMT) with a galvanised finish to be used with propriety EMT couplings, connectors and thread adapters, all parts to be Underwriters Laboratories (UL) approved. However, only heavy gauge conduit shall be used from the cold box penetration to the junction box connection (see Section 8).
7.3.3 Generally, conduits shall be run by the shortest distance to the cold box face and shall not be anchored, except when running parallel with and just inside the cold box face. Conduits shall not be supported from vessels, equipment, or cold piping other than the parent pipe. If absolutely necessary, the conduits may be clamped to the parent pipe; they must never be welded. No welded conduit supports shall be used whatsoever.
7.3.4 Conduit runs just inside the cold box face shall follow structural members and shall not span fixed or removable panels that might at some time be cut or removed for access to cold box internals.
7.3.5 Conduit runs internal to cold boxes shall be securely supported from main structural members by a suitable conduit clamp. This may be in the form of a propriety item purchased by the cold box supplier or fabricated item manufactured by the cold box supplier. The conduit must not be welded directly to structural members.
7.4 Conduit description for cold cans: Flexible conduit shall be an uncovered stainless steel, 316 flexible type, suitable for high temperature service.
7.4.1 Fittings: Flexible conduit fittings shall be stainless steel, and be of propriety type, with one end male thread and the other suitable for connection to conduit described in paragraph 7.4.
7.4.2 The rigid conduit run within the cold can shall be either of a heavy-gauge rigid stainless steel construction, suitable for thread cutting to BS 4568, or heavy-gauge rigid copper-free aluminium to be used with propriety condulet fittings, all UL approved. However, only heavy gauge conduit shall be used from the cold can penetration to the junction box connection (see Section 8).
7.4.3 Generally, conduits shall be run the shortest distance to the cold can face and shall not be anchored except where specified, either on vessel pads or column support steelwork. Conduits shall be supported only on vessels in a circumferential plane, and only off aluminium support brackets in predetermined positions supplied by vessel supplier.
7.4.3.1 If pipe-installed elements are used, conduit may be clamped to parent pipe. In either case, conduit must never be welded. Welded conduit supports shall never be used.
7.4.4 Vertical conduit runs inside the cold can assembly shall follow column support steelwork, with generous allowance for expansion requirement as in paragraph 7.6.
7.4.5 Conduit runs internal to a cold can shall be securely supported by a suitable conduit clamp, as specified in paragraphs 7.4.3 and 7.4.4. This may be in the form of a propriety item purchased by the cold can supplier or a fabricated item manufactured by the cold can supplier. The conduit must not be welded directly to structural members.
7.5 Conduit junctions shall be made with pull boxes to BS 4568 or condulets with UL approval.
7.5.1 To allow for expansion requirements, the maximum amount of slack wire consistent with neat installation shall be left in each junction enclosure.
7.6 Where the conduit connects with the next conduit junction enclosure or fittings at the cold box/can face, straight conduit runs in excess of 2 m (8 ft) internal to the cold box/can shall be fitted with a flexible connection assembly comprising of items described in paragraphs 7.3, 7.3.1, 7.4, and 7.4.1.
7.7 Care must be taken during conduit installation to ensure that all ends of the conduit are cleaned and de-burred, particularly where joins are to be made, to prevent the scuffing of the cable insulation when cable pulling.
7.8 Supports for conduit shall be located as follows:
| Conduit size | Maximum Interval Between Clamps |
| 20 mm or 3/4 in | 1.5 m or 4′ – 0″ |
| 25 and 32 mm or 1 and 1 1/2 in | 2.0 m or 7′ – 0″ |
7.9 Cold boxes shipped to site unpacked and with internal conduits installed shall be complete with shipping supports and anchors fitted as required. These supports shall be painted red for identification and will be removed before insulation packing is started. The cold box supplier shall ensure that a list of all temporary supports, and a drawing or sketch showing their locations, is shipped to site.
7.10 A skin-type temperature element shall be bolted to a stud that has been pre-welded to the pipe by the piping contractor or cold box/can fabricator. Cable tails shall be fed into a length of flexible conduit before continuing in rigid conduit to the junction box. The flexible conduit opening shall start as close as possible to the measuring point and shall be supported by wrapping to the parent pipe with sufficient Teflon tape to provide a secure installation.
7.11 Maximum number of cables per conduit size shall be as follows: 20 mm or 3/4″: 2 pairs or 2 triads or 2 quads 25 mm or 1″ :12 pairs or 6 triads or 6 quads 32 mm or 1 1/2″ : 20 pairs or 10 triads or 10 quads
7.12 When cold boxes/cans are to be H2 purged, all conduit circuits inside the cold box/can shall be interconnected to enable the entire conduit system to be purged of air with N2 from one source point external to cold box/can (see paragraph 8.4).
8. JUNCTION BOXES
8.1 The multiway junction box shall be weatherproof and generally made of a glass-reinforced polyester unless specified as stainless steel by Air Products. The boxes shall be filled with sufficient terminals of a feed-through clamp-type construction to allow for connection of all internal duplex temperature elements plus 10% spare.
8.2 The junction box shall be spaced off from the cold box/can face by 75 mm (3 in) minimum to prevent any possible frost accumulation on the junction box and allow for maintenance of the painted surface of the cold box/can.
8.3 All external entries into the junction box shall be via the bottom entry plate.
8.4 The conduit penetrations from inside the cold box/can to outside for a nonhazardous installation is via a threaded section of heavy-duty conduit of a suitable size, with nuts and lead sealing washers each side of the penetrated panel. They shall be positioned just below the final cable junction box location and consistent to allow this conduit protrusion to be routed via a series of screwed conduit fittings to a seal unit just before connection with the junction box.
8.4.1 For a hazardous installation, the conduit penetration from the cold box/can shall be welded, and subsequent fittings to the seal unit shall all be of a welded type or seal welded before cable installation.
8.4.2 If the cold box/can is to be H2 purged, a suitable steel socket weld pipe tee, plain one end, pipe nipple and screwed pipe cap shall be fitted to one of the conduit runs between the cold box/can face and the seal unit, to allow N2 purging of the conduit system before the cold box/can being H2 purged. The screwed cap shall be seal welded to the nipple after N2 purging (see installation details on project drawings).
8.5 The seal unit mentioned in paragraph 8.4 shall be a “CROUSE-HINDS” type “EYS” Series, used in conjunction with “CROUSE-HINDS” “CHICOA” sealing compound and “CHICO X” fibre dam to achieve a gas-tight seal and thereby limit gas flow from the conduit system to the junction box.
9. TESTING
9.1 Visual Check
9.1.1 Check that the conduit system complies with the requirements of this specification and is generally in accordance with the project drawings; also that the installation is secure and free from damage.
9.1.2 Check that the cable quantities in conduits do not exceed the requirements in paragraph 7.11.
9.1.3 Check that all cable ferrules are fitted, are of the correct type, and have the correct ferrule numbers at both ends.
9.1.4 Check that the correct cable type has been used.
9.2 Cable Check
9.2.1 After installation of the cable and wiring to the junction box mounted on the cold box/can face, but before connection of the thermal elements, the cable and conduit installation shall be tested as follows: Using a “Megger” or similar device, check each cable and record the resistance of each of the following: -Core to core – Core to cable screen – Core to earth – Cable screen to cold box/can steelwork (earth) Minimum resistance must be 500 k ohms at least 100V.
9.2.2 After installation and connection of the elements, the following checks shall be made, using preferably a Digital Multimeter (DMM) on a resistance range. If such an instrument is not available, an analogue-type meter set on a resistance range may be used. Under no circumstances is a high voltage device (such as a Megger) to be used. For each cable/element, check and record the resistance of each of the following: – Core to core – Core to cable screen – Core to earth – Cable screen to cold box/can steelwork (earth) Ambient temperature shall also be recorded.
Note: For thermocouples, the core to core readings will show a small resistance (of the order of 0–25 ohms) through the element, whilst RTDs will show either slightly greater than 100 ohm, or a small resistance (of the order of 100–110 ohms).
9.3 Functional Check
9.3.1 For RTDs, after element connection and wiring is completed, and before the element head being fitted, a calibration continuity check is to be performed as follows.
9.3.1.1 A 100 ohm resistor test assembly is to be temporarily connected to the element head between the terminal connections “white” and “red”(1) as shown in Figure 1.
9.3.1.2 The resultant readings are to be read off at the junction box terminals with a DMM or a bridge instrument set on a resistance range.
9.3.1.3 The readings are to be read between “white” and “red”(1), and “white” and “red”(2); these should be within the normal range of 52 ohm and 56 ohm respectively. A final reading between “red”(1) and “red”(2) should result in a reading of <2 ohm.
9.3.1.4 The results shall be recorded on the test record. If the results are outside those noted above, then further investigation is required. Either a fault exists which must be rectified, or the readings are outside the standard range as a result of long route lengths and/or high/low ambient temperatures. Appendix A gives guidance on the expected effects of route length and ambient temperature.
Figure 1
9.3.2 For thermocouples, after correcting for the “cold” junction temperature, the calibration of each element shall be checked by immersion in a cryogenic fluid [either liquid nitrogen (LIN) or liquid argon (LAR)] at ambient atmospheric pressure. A DMM or potentiometric instrument shall be used to measure the EMF (mV), and the resultant temperature shall be read from the temperature/mV chart for the device being tested. Both the measured EMF, and the resultant temperature shall be recorded for each device. If the temperature reading is not within ± 3°C of the actual temperature, a fault exists and must be rectified.
9.4 Final Installation Check
9.4.1 After the testing outlined in the previous paragraphs, the resistor test assembly should be removed, and the following checks performed: Each element shall be checked for correct physical installation within the body and that the bayonet connection is secure. Each terminal in the element head shall be checked to ensure that it is tight, and the conductors are secure and undamaged. Each head shall be checked to ensure that there is no risk of cores or screens shorting to the head casing or other terminals. Each head cover and head lock nut shall be checked for tightness. Each element shall be checked for secure installation in the thermowell.
Note: If damage occurs to any temperature elements or cable during installation or testing, the elements or cable shall be replaced. Under no circumstances shall repairs to elements be performed, without written approval from the Air Products design engineer.
9.5 Checks During Box Packing
9.5.1 During the packing of the cold box thermal insulation, continuity and insulation resistance of each of the duplex circuits for each point shall be monitored when the level of insulation is just below and again when it is just above the location of the temperature element.
9.5.2 The Air Products supervising engineer shall be informed immediately if any fault is found.
10. TEST RESULTS
10.1 All test results shall be recorded as specified in this document and shall be copied: As required by the fabricator’s internal procedures. To Air Products Inspection who shall distribute a copy to interested parties.
Appendix A Recommended Action In the Event of Failing a Cable or Functional Check
A1. CABLE CHECKS
A1.1 Failing a cable check indicates a cable or termination fault which must be rectified. Insulation resistance may be caused by moisture/humidity in the environment.
A2. FUNCTIONAL CHECKS
A2.1 Failing a functional check suggests that there could be a wiring or an RTD fault.
A2.2 However, long cable runs, high ambient temperatures, or even very low ambient temperatures can cause reading to be outside the normal limits listed in Section 9.3.
A2.3 The predicted test results change with ambient temperature and route length in accordance with Table 1.
Table 1 Predicted Functional Test Results with Temperature and Route Length
| Temp (⁰ C) | Installed Length (m) | RTD value (Ω) | Resistor value (Ω) | RTD and Resistor in parallel (Ω) | Resistance of cable (1 wire) (Ω) | Red to Red Test (Ω) | White to Red Test (Ω) |
| 0 | 5 | 100.0 | 100.0 | 50.0 | 0.1 | 0.2 | 50.2 |
| 10 | 5 | 103.9 | 103.9 | 52.0 | 0.1 | 0.2 | 52.2 |
| 20 | 5 | 107.8 | 107.8 | 53.9 | 0.1 | 0.2 | 54.1 |
| 30 | 5 | 111.7 | 111.7 | 55.8 | 0.1 | 0.2 | 56.1 |
| 40 | 5 | 115.5 | 115.5 | 57.8 | 0.1 | 0.2 | 58.0 |
| 50 | 5 | 119.4 | 119.4 | 59.7 | 0.1 | 0.2 | 59.9 |
| 0 | 20 | 100.0 | 100.0 | 50.0 | 0.4 | 0.9 | 50.9 |
| 10 | 20 | 103.9 | 103.9 | 52.0 | 0.4 | 0.9 | 52.8 |
| 20 | 20 | 107.8 | 107.8 | 53.9 | 0.4 | 0.9 | 54.8 |
| 30 | 20 | 111.7 | 111.7 | 55.8 | 0.4 | 0.9 | 56.7 |
| 40 | 20 | 115.5 | 115.5 | 57.8 | 0.4 | 0.9 | 58.7 |
| 50 | 20 | 119.4 | 119.4 | 59.7 | 0.4 | 0.9 | 60.6 |
| 0 | 45 | 100.0 | 100.0 | 50.0 | 1.0 | 2.0 | 52.0 |
| 10 | 45 | 103.9 | 103.9 | 52.0 | 1.0 | 2.0 | 53.9 |
| 20 | 45 | 107.8 | 107.8 | 53.9 | 1.0 | 2.0 | 55.9 |
| 30 | 45 | 111.7 | 111.7 | 55.8 | 1.0 | 2.0 | 57.8 |
| 40 | 45 | 115.5 | 115.5 | 57.8 | 1.0 | 2.0 | 59.8 |
| 50 | 45 | 119.4 | 119.4 | 59.7 | 1.0 | 2.0 | 61.7 |
| 0 | 65 | 100.0 | 100.0 | 50.0 | 1.4 | 2.9 | 52.9 |
| 10 | 65 | 103.9 | 103.9 | 52.0 | 1.4 | 2.9 | 54.8 |
| 20 | 65 | 107.8 | 107.8 | 53.9 | 1.4 | 2.9 | 56.8 |
| 30 | 65 | 111.7 | 111.7 | 55.8 | 1.4 | 2.9 | 58.7 |
| 40 | 65 | 115.5 | 115.5 | 57.8 | 1.4 | 2.9 | 60.6 |
| 50 | 65 | 119.4 | 119.4 | 59.7 | 1.4 | 2.9 | 62.6 |
| 0 | 85 | 100.0 | 100.0 | 50.0 | 1.9 | 3.7 | 53.7 |
| 10 | 85 | 103.9 | 103.9 | 52.0 | 1.9 | 3.7 | 55.7 |
| 20 | 85 | 107.8 | 107.8 | 53.9 | 1.9 | 3.7 | 57.6 |
| 30 | 85 | 111.7 | 111.7 | 55.8 | 1.9 | 3.7 | 59.6 |
| 40 | 85 | 115.5 | 115.5 | 57.8 | 1.9 | 3.7 | 61.5 |
| 50 | 85 | 119.4 | 119.4 | 59.7 | 1.9 | 3.7 | 63.4 |
A2.4 Allowing for ambient temperature measurement variations, and approximate route length measurement, then the test may be considered successful if the measured values of the: Red-Red Test is < 0.5 W greater than the corresponding value in Table 1. White-Red Test is within + 2 W of the corresponding value in Table 1.
A2.5 Note that: At route lengths >45m, installations should be expected to fail the Red-to-Red W test. At 10°C, installations should be expected to pass the Red-to-White W test for all route lengths up to and beyond 85m. At increasing ambient temperatures, installations should be expected to fail the Red-to-White W test for decreasing route lengths. At 30°C, installations should be expected to fail for all realistic route lengths. At <10°C, installations may begin to fail the Red-to-White W test for shorter route lengths.
A3. ADJUSTMENT OF FUNCTION CHECK TO COMPENSATE FOR AMBIENT TEMPERATURE AND ROUTE LENGTH
A3.1 Table 1 demonstrates that the standard acceptance criteria given in Section 9.3, while appropriate for the majority of checks, can cause problems for long route lengths and for high/low ambient temperatures.
A3.2 In the event of an installation failing the tests in Section 9.3, the installation may still be considered correct if the measurements correspond to the expected valves given in Table 1.
A3.3 In accordance with Table 1, the following simple corrections may be applied to the standard acceptance criterion to compensate for ambient temperature and route length: The Red-to-Red test may be corrected for longer route lengths by setting the acceptance criteria to <0.05W /m route length. For example, for a 60m route length, the acceptance criterion may be adjusted to <3W in place of the standard <2W criterion. The White-to-Red test may be corrected for different ambient conditions by applying a correction of 0.2W/°C for ambient temperatures above or below 10oC. For example, for a 20oC ambient temperature, the acceptance criterion may be adjusted from 54 to 58W in place of the standard 52 to 56W criterion.