1.1- SOW for 7T Vertical Field Magnet.docx

Statement of Work for 7T Vertical Field Magnet with Helium-3 Dipper and Dilution Refrigerator Insert Statement of Work for 7T Vertical Field Magnet with Helium-3 Dipper and Dilution Refrigerator Insert

Background The Department of Commerce and the National Institute of Standards and Technology (NIST) have developed a major national facility for neutron scattering. The NIST Center for Neutron Research (NCNR) is a user facility serving the needs of over 900 visiting researchers per year who come to perform neutron scattering experiments.

Measuring the magnetic field dependent properties of materials is a critical part of the NCNR mission, which often requires the use of liquid helium to cryogenically cool the magnet and the sample materials. Liquid helium is a non-renewable resource and the financial cost of using it is increasing every year. To operate more sustainably a transition to cryogen-free systems, i.e. “dry magnets” is desirable. Dry magnets use a closed-cycle refrigerator (CCR) to conductively cool the magnet coils, requiring no addition of any cryogens at any time during preparation, operation, or recovery from magnet quench. This sample environment equipment must operate with high reliability and accuracy across the wide range of instruments and sample measurement conditions, be simple and safe to operate, with safeguards to protect both the equipment and personnel during operation.

Purpose The objective of this procurement is to purchase one 7 Tesla cryogen-free superconducting magnet with a Helium-3 Dipper Insert and a Dilution Refrigerator Insert. This “Magnet System” will be used for sample environment operation at all appropriate neutron user instruments at the NCNR.

System Description The full system includes one cold-bore superconducting magnet, two sample positioners, one dilution refrigerator system with insert, one helium-3 dipper, and all necessary additional items to make turn-key systems as described below. The “Ultra-Low Temperature (ULT) Inserts” refer collectively to the dilution refrigerator and the helium-3 dipper. The “Magnet System” is the full turnkey system which includes all equipment related to the operation of the magnet and sample well, exclusive of the ULT inserts. The “Variable Temperature Interface (VTI)” is the interface between the Magnet System and the ULT inserts and is also known as the Sample Well.

Attachments

1.1. Symbol Diagram for variables shown in Additional Physical Dimensions Table

1.2. Dimensional Plan View of MACS Mezzanine

1.3. NCNR standard pinout ribbon wire

Specification

1.4. Full System Requirements

1.4.1. The entire system must be cryogen free (no liquid helium or liquid nitrogen required) and must only require an initial charge of Helium gas to initialize a self-cooling cryogenic system.

1.4.2. Circulation Systems

1.4.2.1. All circulation pumps must be oil-free (aka “dry”), Kashiyama Neodry Series, or equivalent.

1.4.2.2. Minimum rate 500 L/min.

1.4.2.3. Circulating helium must have a reliable trap for filtering the mixture in order to remove impurities. The cryogen free requirement does not include the liquid nitrogen necessary for the circulation trap(s).

1.4.2.4. There must be a mechanism to regenerate the trap(s).

1.4.3. NCNR will provide the 3He gas for the 3He/4He mixtures.

1.4.3.1. The 3He/4He mixtures must be optimized by the contractor and the contractor must document the total amount of 3He gas in each system. The contractor must return all unused 3He gas at the time of system delivery. It is acceptable to have the remainder of the 3He to be returned in the “mixture” form if the mixture is documented.

1.4.4. The VTI internal dimensions must be compatible with both existing NCNR dilution refrigerator inserts. The VTI interface “1K pot” must be compatible with existing NCNR dilution refrigerators. NCNR will provide dimensions.

1.4.5. The ULT inserts external dimensions must be compatible with the VTI internal dimensions for this magnet system and the existing NCNR magnet system. NCNR will provide dimensions.

1.4.6. All vacuum spaces must be leak-tight to 1 x 10-9 atm-cm3/sec.

1.4.7. All control and communications equipment for the magnet system, 3He Dipper, and DF must operate independently of each other.

1.4.8. Contractor must provide all airside cables for control and communication. NIST will provide pinouts for all Fisher connectors.

1.4.9. Computer interface standards that must be available for all control and communication equipment:

1.4.9.1. RS-232 (Serial)

1.4.9.2. Ethernet (TCP/IP)

1.4.9.3. IEEE-488.2 (GPIB)

1.4.10. Must meet the following table properties:

1.5 +/- 0.10K

1.5. Magnet System Requirements

1.5.1. The closed-cycle refrigerators must include 1-2 cold heads, 2-4 helium gas flexlines, and 1-2 air-cooled compressors. No recirculating water packs or external water service connections are permitted. No multi-part indoor/outdoor air units are permitted.

1.5.2. The magnet temperature must not increase by more than 1 Kelvin during sample change with ULT inserts or sample positioners (as long as this temperature rise does not interfere with the super conducting phase of the magnet). The system must have sufficient cooling power to independently cool the magnet coils and the sample space.

1.5.3. All circulating helium in the magnet system must be isolated from the inner volume of the VTI (variable temperature interface) at all times. The system must be designed so that circulating helium cannot mix with the helium for sample change.

1.5.4. Magnetic field direction at the sample position must be vertical.

1.5.5. The magnet coils must be symmetric.

1.5.6. The coils may be either tapered or non-tapered. Tapered is preferred.

1.5.7. The magnet must have a center tap to allow small vertical offset of the magnetic field center.

1.5.8. The magnet coils must be supported sufficiently to withstand radial and axial forces due to ferromagnetic materials in the surrounding environment.

1.5.9. The contractor must provide stray field models for the magnet.

1.5.10. NIST will provide analysis of forces due to the surrounding environment.

1.5.11. The magnet coils must be shielded by neutron absorbing materials, and the shielding must not contain any cadmium near the split.

1.5.12. Maximum Aluminum in Beam Path: MABP is the uniform total thickness of aluminum alloy in the beam path from outside the cryostat to the sample and then exiting the cryostat, for the entire azimuthal beam path access window (w). MABP does not include any thickness of ancillary equipment inserted into the well, such as the sample can, sample itself, or the vacuum can of a dilution refrigerator.

1.5.12.1. The sample position is defined as the intersection of the neutron beam centerline and the central axis of the magnet.

1.5.12.2. Azimuthal Beam Path Window (w): Single azimuthal section through which the neutron beam can pass to the sample position and out again without encountering any material except aluminum and the sample.

1.5.12.3. Only uniformly distributed, high purity aluminum alloy is permitted in the Azimuthal Beam Path Window.

1.5.12.4. Dark Angle (DA): All connections between the magnet coil split sections should be concentrated in a single azimuthal section no larger than DA=360-w degrees.

1.5.13. Incident Beam Access Window: This is an exception to the uniformity requirement for the azimuthal beam path window. The magnet separation supports must include one window which consists of radially aligned entry holes for the incident beam, in which there is no material at all. The size of the window must be 40mm wide and extend the full height of the coil separation. The access window must be close to the Dark Angle, so that the azimuthal beam path window is still a single section.

1.5.14. Persistent mode not permitted, magnet must always run in direct current mode.

1.5.15. Must meet the following parameters (Additional Physical Dimensions Table):

Value

no worse than 0.6% in 1cm dsv and 1% in 2cm dsv

2.0

(+/- 4)

+/-1mm

1.6. Dilution Refrigerator Requirements

1.6.1. The dilution refrigerator system must be self-contained and include all necessary equipment for complete turnkey operation when inserted into any compatible VTI. This includes the flow control system, insert, circulating pump, valves, cabling, etc.

1.6.2. The dilution refrigerator must be compatible with this magnet and the NCNR’s existing 10T magnet. NCNR will provide dimensions for existing equipment.

1.6.3. Only uniformly distributed, high purity aluminum alloy is permitted in the sample window.

1.6.4. The system must provide 360 degree access to the sample in the horizontal scattering plane of the sample window without intersecting any liquid cryogens or any part of the cooling system.

1.6.5. Sample mounting surface description:

1.6.5.1. The flat sample mounting surface is a 5/16-18 UNC-2B threaded 10 millimeter length full depth, located on center axis of insert.

1.6.5.2. The flat surface of the sample mount is 50 millimeter above the neutron beam centerline when the cryostat is in its nominal position.

1.6.6. The vacuum flange of the insert must provide flexibility to manually adjust the insert's vertical position by up to +/- 30mm and a mechanism to prevent unintentional rotation of the insert within the VTI.

1.6.7. The IVC (Inner Vacuum Can) must include a method or mechanism to remove IVC without mechanical shock to the sample. Knocking method is not acceptable.

1.6.8. Must meet the following parameters:

Value

0.050 +/- 0.001K

0.5

1.7. Helium-3 Dipper Requirements

1.7.1. The helium-3 dipper system must be self-contained and include all necessary equipment for complete turnkey operation when inserted into any compatible VTI.

1.7.2. The helium-3 dipper must be compatible with this magnet and the NCNR’s existing 10T magnet.

1.7.3. Only uniformly distributed, high purity aluminum alloy is permitted in the sample window.

1.7.4. The system must provide 360 degree access to the sample in the horizontal scattering plane of the sample window without intersecting any liquid cryogens or any part of the cooling system.

1.7.5. Sample mounting surface description:

1.7.5.1. The flat sample mounting surface is a 5/16-18 UNC-2B threaded 10 millimeter length full depth, located on center axis of insert.

1.7.5.2. The flat surface of the sample mount is 50 millimeter above the neutron beam centerline when the cryostat is in its nominal position.

1.7.6. The vacuum flange of the dipper has to provide flexibility to manually adjust the insert's vertical position by up to +/- 30mm and a mechanism to prevent unintentional rotation of the insert within the VTI.

1.7.7. The IVC (Inner Vacuum Can) must include a method or mechanism to remove IVC without mechanical shock to the sample. Knocking method is not acceptable.

1.7.8. Must meet the following parameters:

Value

0.300 +/- 0.001K

0.5

1.8. Control and Communication -Magnet System

1.8.1. Magnet System must include the following temperature sensors:

1.8.1.1. 6 sensors on the magnet, 1 sensor on VTI, 1 sensor on each sample positioner.

1.8.1.1.1. Cernox CX-1030 or equivalent.

1.8.1.1.1.1. Low magnetic field- induced errors, ΔT/T (%) < 1% at 4.2K and 12T

1.8.1.1.1.2. Excellent resistance to ionizing radiation

1.8.1.1.1.3. Temperature range 1.0 Kelvin to 325 Kelvin

1.8.1.2. Contractor must provide the wiring pinouts and sensor curves.

1.8.1.3. System must include a temperature controller to monitor, control, and log all temperature sensors.

1.8.1.4. The temperature controller(s) ramp rate must enable the temperature on the VTI and sample positioner to be linearly varied to cool or warm the sample at a user defined rate ranging from 0.1 Kelvin/min or lower to 5 Kelvin/min or larger and have a temperature stability of ± 500 mK or better over the entire operating range.

1.8.2. Sock, if present, must have a heater. Heater will be manually controlled.

1.8.3. VTI needle valve, if present, must have a heater on the capillary space. Heater will be manually controlled.

1.8.4. Magnet ramp rate must be defined at all field values, and safety limits documented.

1.8.5. Magnet ramp rate must be adjustable by software or protocols which are within NCNR control.

1.8.6. The system must include software controlled temperature protection for magnet, with source code provided for NCNR control.

1.9. Control and Communication- Dilution Refrigerator

1.9.1. AC Resistance Bridge and temperature controller optimized for <50mK temperature control:

1.9.1.1. Lakeshore 372

1.9.1.2. 4 channels for temperature measurement.

1.9.1.3. Relay box with 16 inputs to scan all sensors at a user defined rate.

1.9.2. Control interface of the gas handling system must be touch screen.

1.9.3. System must include 1 temperature sensor as close to the sample position as possible:

1.9.3.1. The sensor must have linear dependence of magneto-resistance vs magnetic field within 0 – 12T range.

1.9.3.2. If the temperature sensor’s readings shift more than 5% due to magnetic field application, then magnetic field calibration at 50mK is required for the sensor.

1.9.3.3. Excellent resistance to ionizing radiation.

1.9.3.4. Temperature range .01 - 100 Kelvin.

1.9.3.5. Contractor must provide documentation and electronic copies of the sensor calibration curves.

1.9.4. System must include two (2) RuO2 temperature sensors on the mixing chamber.

1.9.4.1. One sensor must be calibrated for 0.02-40 Kelvin.

1.9.4.2. One sensor must be calibrated for 0.3K-300K.

1.9.4.3. Excellent resistance to ionizing radiation.

1.9.4.4. Small and linear with magnetic field at base temperature magneto resistance.

1.9.4.4.1. If the temperature sensor’s readings shift more than 5% due to magnetic field application, then magnetic field calibration at 50mK is required for the sensor.

1.9.4.5. System must include one 24 pin Fischer connector for sensors and heaters using NCNR standard pinout ribbon wire.

1.9.4.6. System must include one 24 pin Fischer connector for NCNR internal use with standard pinout to ribbon wire.

1.9.4.7. Must provide Software control of valves, flow rates, and source code.

1.9.4.8. The temperature controller(s) ramp rate must enable the temperature on the sample to be linearly varied to cool or warm the sample at a user defined rate ranging from 0.1 Kelvin/min or lower to 5 Kelvin/min or larger and have a temperature stability of ± 500 mK or better over the entire operating range.

1.10. Control and Communication -Helium-3 Dipper

1.10.1. Temperature controller optimized for <50mK temperature control.

1.10.1.1. Lakeshore 336

1.10.1.2. 4 channels for temperature measurement.

1.10.2. System must include 2 RuO2 temperature sensors on the mixing chamber:

1.10.2.1. One sensor must be calibrated for 0.02-40 Kelvin.

1.10.2.2. One sensor must be calibrated for 0.3K-300K.

1.10.2.3. Excellent resistance to ionizing radiation.

1.10.2.4. Small and linear with magnetic field at base temperature magneto resistance.

1.10.2.4.1. If the temperature sensor’s readings shift more than 5% due to magnetic field application, then magnetic field calibration at 50mK is required for the sensor.

1.10.2.5. System must include one 24 pin Fischer connector for sensors and heaters using NCNR standard pinout ribbon wire. Contractor must provide the airside cable.

1.10.2.6. System must include one 24 pin Fischer connector for NCNR internal use with standard pinout to ribbon wire.

1.10.2.7. The temperature controller(s) ramp rate must enable the temperature on the sample to be linearly varied to cool or warm the sample at a user defined rate ranging from 0.1 Kelvin/min or lower to 5 Kelvin/min or larger and have a temperature stability of ± 300 mK or better over the entire operating range.

1.11. Electrical Requirements

1.11.1. The Contractor must provide the full system with cables and plugs for direct connection to electrical service. The full system must be configured to operate using only a combination of the following available electrical services:

1.11.1.1. 250 Volt/ 3-phase/ 60 Amp, NEMA 15-60 plug (no more than 2 total)

1.11.1.2. 208 Volt/ 3-phase/ 30 Amp, NEMA L21-30 plug (no more than 2 total)

1.11.1.3. 220 Volt/ 1-phase/ 30 Amp, NEMA L7-30 plugs (no more than 2 total)

1.11.1.4. 120 Volt/ 1-phase/ 20 Amp, NEMA 5-20 plugs

1.11.2. Maximum steady state power consumption for each closed-cycle refrigerator:

1.11.3. 20.7 kWatts for 250 V/3-phase/ 60 Amp service

1.11.4. 8.7 kWatts for 208 V/3-phase/ 30 Amp service

1.11.5. 5.3 kWatts for 220 V/1-phase/ 30 Amp service

1.11.6. 1.9 kWatts for 120 V/1-phase/ 20 Amp service

1.12. Lifting and Transport

1.12.1. The dimensions of the facility doorways through which the system must pass are 2100 millimeters height and 830 millimeters width.

1.12.2. Contractor must design and build a cart (trolley) for the magnet system, such that all components of the magnet system are fully contained within the transportable cart:

1.12.2.1. The entire magnet system must pass through doorways with the specified dimensions.

1.12.2.2. Footprint of the system cart is limited by the mezzanine space at MACS. Dimensional drawings of the mezzanine will be provided by NCNR.

1.12.2.3. Cart must be designed for crane lifting and be in accordance Standard Engineering codes requirements. A lift test certification is required.

1.12.3. Contractor must design the magnet itself for crane lifting off of the cart and onto the instrument goniometer.

1.12.3.1. Magnet lifting must be in accordance Standard Engineering codes requirements. A lift test certification is required.

1.12.4. Contractor must design and build a cart (trolley) for the dilution refrigerator system, such that all components of the dilution refrigerator are fully contained within the transportable cart:

1.12.4.1. The entire dilution refrigerator must pass through doorways with the specified dimensions.

1.12.4.2. Cart must be designed for crane lifting and be in accordance Standard Engineering codes requirements. A lift test certification is required.

1.12.5. Contractor must design the ULT inserts themselves for crane lifting into and out of the VTI:

1.12.5.1. ULT inserts lifting must be in accordance Standard Engineering codes requirements. A lift test certification is required for each ULT insert.

1.12.6. If sample positioner requires to be lifted with crane, the crane lifting must be in accordance with Standard Engineering codes requirements. A lift test certification is required.

1.13. Sample Positioning

1.13.1. Sample Rotation: Design of the interface between the VTI and the ULT inserts and sample positioners must include rotational adjustment, and this adjustment must be remotely controlled to the provided specifications. The mechanism for adjustment must be removable in order to meet system height requirements.

1.13.2. Sample Translation: Design of the interface between the VTI and the ULT inserts and sample positioners must include the option of separate vertical adjustment, and this adjustment must be remotely controlled to the provided specifications. The mechanism for adjustment must be removable in order to meet system height requirements.

1.13.3. Must meet the following parameters:

1.14. Deliverables

1.14.1. Conceptual design documents and drawings (*.pdf format) includes a draft schedule. Draft schedule must include the date by which the contractor will require delivery of the Helium-3 provided by NIST. Due with bid for project.

1.14.2. Kickoff meeting. No later than 2 weeks after award of contract.

1.14.3. Preliminary design documents and drawings (*.pdf format). Must include temperature sensor information such as sensor type, tolerances, location of installation, and curves. Due 12 weeks after award of contract.

1.14.4. Structural Analysis Report (*.pdf format). The structural analysis of the support structure for the superconducting magnet system will validate that the design meets the vertical and horizontal force requirements. The structural analysis must show that the design meets these requirements with a minimum safety factor of 2.0. Due 18 weeks after award of contract.

1.14.5. Fringe/Stray Field Analysis Report (*.pdf format). Due 18 weeks after award of contract.

1.14.6. Two (2) hard copies of all final documentation (calculations, reports, drawings and final schedule) and user manual. User-manual must include (at a minimum) operation, maintenance, bill of materials, list of recommended spare parts and troubleshooting instructions. Due 2 weeks after final acceptance testing.

1.14.7. All final design documents and user-manual (*.pdf format). Due 2 weeks after final acceptance testing.

1.14.8. Note: conceptual through final design steps must be presented to the government’s technical representative. The contractor may proceed to the next step after the previous step has been reviewed and approved by the government's technical representative.

1.14.9. Conduct bi-weekly status and planning meetings (kickoff meeting being the first one) from award of contract to completion of the contract. Meetings can be done via conference or video call. Contractor must send written summaries (*.pdf format) after each meeting to NIST for review and concurrence. Meeting schedule may be modified as necessary by mutual agreement between the contractor and the government’s technical representative.

1.14.10. Factory Acceptance Testing (FAT). The factory test report must be delivered to NIST not later than 16 months after award of contract, and prior to shipping the system to NIST. The test report serves to validate that specifications have been met prior to delivery to NIST.

1.14.10.1. NIST personnel plan to be present for the FAT, from warm system to base temperature.

1.14.10.1.1. Duration of visit between 5 to 15 days, as necessary.

1.14.10.1.2. Training for up to 2 NIST personnel provided during the FAT. Training will include preparation, operation, and maintenance of the magnet system.

1.14.10.2. The factory test report must provide the following information at a minimum:

1.14.10.2.1. Helium leak test on the vacuum shroud at room temperature and at operating temperature for the superconducting magnet.

1.14.10.2.2. Record of temperature sensor outputs for all magnet system sensors during the cooldown and warmup tests.

1.14.10.2.3. Cool-down time from room temperature to magnet operating temperature.

1.14.10.2.4. Maximum magnetic field achieved. The magnetic field must be maintained at maximum value for a minimum of 8 hours to be considered a successful test.

1.14.10.2.5. Current in the magnet power supply at maximum field.

1.14.10.2.6. Ramping times from zero field to 80% of maximum field, and from zero field to +/- 100% of maximum field.

1.14.10.2.7. Magnetic field homogeneity at the sample position.

1.14.10.2.8. Fringe field measurements that confirm the fringe field map that was provided in the design.

1.14.10.2.9. Information regarding magnet quenches that may have occurred during testing. This will include the field at which quench occurred, and any anomalous behavior leading up to the quench.

1.14.10.2.10. Timestamped record of temperature sensor outputs for all ULT insert sensors and sample sensors during the sample cooldown and warmup tests.

1.14.10.2.10.1. Cool-down of the sample from room temperature sample insertion to operating temperature.

1.14.10.2.10.2. Hold time for the sample at base temperature for a period of no less than 50 hours at base temperature.

1.14.10.2.10.3. Warming the sample from operating temperature to room temperature and back to operating temperature for sample change.

1.14.11. The magnet system must be delivered, installed, and tested by the contractor at NCNR.

1.14.11.1. The contractor must coordinate with NCNR for the installation.

1.14.11.2. The contractor must be responsible for unpacking the system, performing the setup, installation, and on-site testing. NIST will provide space, electrical power, vacuum pumps, a helium leak detector, a magnetic field sensor, and force gauges. Upon award, any further requirements must be communicated by the contractor prior to arrival.

1.14.11.3. The contractor must provide the recirculating pumps.

1.14.12. Training, in addition to training that may or may not have occurred during the FAT, must occur upon acceptable installation. Training for up to 4 NIST personnel must be provided by the contractor. Training must include preparation, operation, and maintenance of the magnet system.

1.14.13. Installation test report. At the conclusion of installation, the contractor must provide an installation test report. This report must include the following information at a minimum.

1.14.13.1. Helium leak test on the vacuum shroud at room temperature and at operating temperature for the superconducting magnet.

1.14.13.2. Cool-down time from room temperature to magnet operating temperature.

1.14.13.3. Maximum magnetic field achieved. The magnetic field must be maintained at maximum value for a minimum of 8 hours to be considered a successful test.

1.14.13.4. Current in the magnet power supply at maximum field.

1.14.13.5. A table of ramp rates every 1T, and ramping times from zero field to +/- 80% of maximum field, and from zero field to +/-100% of maximum field.

1.14.13.6. Magnetic field homogeneity at the sample position.

1.14.13.7. Fringe field measurements that confirm the fringe field map that was provided in the design.

1.14.13.8. Force test measurements that confirm the forces on the magnet as provided in the design.

1.14.13.9. Information regarding magnet quenches that may have occurred during testing. This will include the field at which quench occurred, and any anomalous behavior leading up to the quench.

1.14.13.10. Timestamped record of temperature sensor outputs for all dilution refrigerator sensors and sample sensors during the sample cooldown and warmup tests.

1.14.13.10.1. Cool-down of the sample from room temperature to operating temperature.

1.14.13.10.2. Hold time for the sample at base temperature for a period of no less than 50 hours at base temperature.

1.14.13.10.3. Warming the sample from operating temperature to room temperature and back to operating temperature for sample change.

1.14.14. Supply two (2) hard copies of final documentation and user-manual including (at a minimum) operation, maintenance, bill of materials, list of recommended spare parts and troubleshooting instructions.

1.14.15. Supply final documentation and user-manual in *.pdf format.

Government Responsibilities

1.15. Review and approve conceptual (due with bid), preliminary and final design proposals. No more than 30 days for each review period.

1.16. Provide access to NCNR including experiment areas (work areas). Each individual worker must attend NCNR Radiation Safety Training (1/2-day class) prior to working in a work area.

1.17. Provide the 3He gas for the 3He/4He mixture.

1.18. Assist contractor (provide crane operator, inspect for shipping damage and lost or missing equipment and dispose of shipping and packing material) in unpacking and inspection of the equipment delivered to NIST. The three-week period commencing with the unpacking and inspection of the equipment delivered to NIST will be used for acceptance testing.

Delivery The Contractor must provide and deliver all equipment and documentation (both electronic and hardcopy) specified herein to NIST within the period of performance.

Periods of Performance The period of performance for the requested task must be 20 months from award of contract.

Place of Delivery of Performance:

FOB NIST Gaithersburg

Warranty.

1.19. A 1 (one) year standard warranty period is required.

1.20. An extended warranty period of 1 (one) year beginning at the end of the standard warranty period is requested as an option.

1.21. All warranties must cover all deliverables, parts, and labor. Over the phone technical assistance, and site visits.

1.22. Software updates for compliance with operating system to be included as part of warranties.

1.23. Contractor must respond to all warranty requests within 24 hours of request.

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