Main keywords for this article are Quality Inspection Levels. Control Valve Testing. Hydrostatic Pressure Test. Valve Travel Test. Dead Band Test. Completely Assembled Valve Hydrotest.
Quality Inspection Levels
When all valves of one purchase order are to be inspected to the same Level, this will be indicated in the General Specification or as a note on the Valves Inspections Checklist – Table IV.
Where valves have different inspection requirements, the Category/Level code will be shown on the Valves Inspections Checklist – Table IV.
Level A Inspection
Vendor’s normal Quality Control procedures are acceptable after review, and no formal inspection by personnel at the vendor’s shop is required.
Level B Inspection
- In addition to vendor’s Level A inspection, the completed valve assembly will be visually inspected for general workmanship, cleanliness, scale, identification, protective coatings, and conformance to purchase specifications.
- The valve size, rating, gasket face finish, and face to face dimension(s) will be checked against specifications, vendor standards, approved vendor drawings.
- Materials of construction will be verified by visual check or by parts marking and vendor’s assembly records. Chemical testing will not be done unless specified.
- Nameplate data is to be verified as to accuracy and completeness.
- The QAR will verify compliance with all special requirements listed on purchase order. Any accessories will be verified to be the correct items and properly mounted, piped, or wired.
- Valve body castings will be visually checked for obvious defects or flaws. The vendor shall advise the QAR of any known repairs to the casting and the procedures used. Vendor shall submit repair procedures for approval prior to fabrication.
- The QAR will verify rust preventative coatings to carbon steel flange gasket surfaces. He shall also verify any specified protective coatings or other coverings have been applied.
- The QAR will inspect all items above (visual examination) and Section (valve travel test), with verification of valve operation without binding or sticking.
- Vendor is to certify compliance with section for hydrostatic test and section for specified seat leakage requirements.
- Dead band test is not required. Valve disassembly is not needed, except at the discretion of the QAR, unless issues of valve operation or conformance to specifications are involved.
Level C Inspection
In addition to Levels A and B inspections, the QAR will witness the seat leakage test, according to section ”Seat Leakage Test”.
Level D Inspection
In addition to Levels A and B inspections, the QAR will witness the body hydrostatic pressure test according to Section ”Hydrostatic Pressure Test”.
Level E Inspection
In addition to Levels A and B inspections, the QAR will witness the final assembly of the valve.
Level F Inspection
In addition to Levels A and B inspections, the QAR will witness any operational tests, for example stroke speed, smoothness of operation, limit switches, solenoid tripping, failure action, leak test, etc, as called for in the purchase order.
Level G Inspection
In addition to Levels A and B inspections, the QAR will witness or verify (or both) any nondestructive testing (NDT) requirements and material specifications called for in the order. This would include such things as material certifications, tests performed at the foundry or forging location, magnetic particle check, or liquid-penetration check of machined surfaces on pressure containment parts, viewing and judging radiographs and verifying repair procedures. Normally, this level of inspection requires detailed specifications in the purchase order and close coordination between QA and Project Engineering.
Level H Inspection
In addition to Levels A and B inspections, the QAR will witness the dead band check according to section 6.6, if specified.
Sample Inspection
If valves are to be sample inspected, the suffix letter “S” will be added to the designated inspection level for selected valves. The QAR will inspect each of these valves in accordance with the designated inspection level. In addition, the QAR will randomly select minimum one valve of the same type (or more, if percent sampling is specified) from each group of valves with inspection levels suffix “S” and perform inspection.
Control Valve Testing
Control valves shall pass each inspection level specified in the purchase order or Valves Inspections Checklist – Table IV. The QAR will witness tests required for all inspection levels.
Hydrostatic Pressure Test
- The control valve assembly, with or without actuator, will be completed before hydrostatic testing..
- The control valve assembly shall be hydrotested as per the test procedure outlined of ISA 75.19.01
- Pressure measurement instrument shall be analog or digital indicating type and shall be used for pressure range between 20 to 80 percent of its range. Test gauge shall have a certified accuracy of ± 1.0 percent and must have a valid test certificate. Use of redundant gauges for pressure measurement is preferred.
- All cavities pressurized in service shall simultaneously be subjected to the hydrostatic shell test pressure. Bellows, packing and trim parts that may be damaged during the hydrostatic pressure test or trim parts that do not affect the pressure boundary need not be installed during the test. The valve body shall be tested without these parts, then re-assembled as a complete valve and re-tested at the design or operating pressure agreed upon by the vendor, or as specified on the purchase order.
a. On bellows sealed valves, the bonnet vent plug shall be removed to check for leakage through the bellows.
b. Valve shall be permanently tagged with the maximum safe working pressure (at application temperature) of the bellows.
- Weld-on nipples or expanders shall be considered as parts of the valve body assembly and shall be included in the hydrostatic test. If it is not practical to test the valve in accordance with this specification, the test procedures may be agreed upon by the vendor (e.g., valve body assembled with fittings of lower pressure rating where it is apparent that the assembly cannot be tested at the valve body pressure rating).
- The valve shall not be painted before hydrostatic testing except with agreement. Where individual pressure containment components have been hydrostatically tested prior to assembly, the final assembly may be painted after final testing.
- Clean potable water shall generally be used for hydrostatic testing. The temperature of the test fluid shall be between 5 deg C to 52 deg C and the pH shall be between 6 to 8.
- Where water cannot be used, other liquids may be used as agreed upon between company and the vendor.
- The valve cavity shall be drained and thoroughly dried with air or nitrogen.
- Hydrostatic testing of stainless steel valves or valves containing stainless steel internals subject to stress by the manufacturing process or operating temperatures above 60 deg C require special consideration. Water shall be steam condensate, de-mineralized water, or clean, potable water with chloride content less than 10 ppm. Potable water up to a maximum of 250 ppm chlorides may be used if the valve is drained immediately and washed out thoroughly with de-mineralized water or steam condensate and dried thoroughly with dry air or nitrogen.
- During hydrostatic test the valve plug shall not be seated on the main seat or on the back seat.
- Weeping or leakage through any pressure containment part or past static seals and any distortion which may cause unsatisfactory performance of the valve shall be cause for rejection.
- After hydrostatic shell testing, the disassembling of the valve is permissible with following measures:
a. New gaskets or seals of the same kind and size are used to reassemble the valve
b. Equivalent size & type of studs and nuts are used with the same torque procedure to re- assemble the valve and ensure to achieve the same pre-test bolt loads result.
c. To ensure proper gasket installation, a leak test shall be performed at lower than the hydrostatic shell test pressure with air or water.
Exception to Completely Assembled Valve Hydrotest
- Component hydrotest at 1.5 times the rated pressure followed by a pneumatic shell test for complete valve assembly at working pressure is allowed with approval. Vendor shall furnish the test documents for the component hydrotest and advise the pressure for the pneumatic test for the assembled valve body.
- Seat Leakage Test
- Control valve seat leakage shall be as specified in ANSI FCI 70-2 and API 598. If the leakage class is not specified, Class I or vendor standard leakage class for the particular valve design is intended.
- In case water cannot be used as testing medium, the use of alternate liquid shall be with written approval by company.
Valve Travel Test
- If the valve equipped with a positioner, it shall be adjusted for full travel over a change in signal pressure between 0.2 to 1 barg with the packing at normal tightness.
- Spring and diaphragm valves without positioner will be checked for bench spring setting values determined by the manufacturer as compared with the actual diaphragm pressure.
- Allowable bench setting tolerances for pneumatic inputs are 0.2 ± 0.01 and 1.0 ± 0.01 barg for full valve travel. Allowable tolerances for electronic inputs are 4 ± 0.1 mA and 20 ± 0.1 mA for full travel.
- In addition to the above, spring and diaphragm valves with positioners will be checked for air pressure to the diaphragm chamber. Bench spring setting values determined by the manufacturer will be compared with the actual diaphragm pressure. This pressure will be read on a separate test gauge. Allowable tolerance is ± 0.03 barg on the span.
- During valve travel tests, all tubing connections, fittings, diaphragm closures, accessories etc. shall be checked for air leak.
- Control Valve Dynamic Performance Specifications
- For definition of dead band, dead time, step response time and overshoot refer to the ISA S75.05.01 Control Valve Terminology.
- For control valve dynamic performance test, the valve shall be assembled with the positioner. Packing shall be tightened as required for the intended service conditions or the hydrostatic test.
- Dynamic performance test methods shall be as per ISA-75.25.01 “Test Procedure for
- Control Valve Response Measurement from Step Inputs”.
Dead Band Test
- Dead band is defined as the range through which an input signal may be varied, with reversal of signal direction, without detectable movement of the valve as measured with a dial indicator of 0.001 inch sensitivity. Dead band test is specified only for critical process control where dead band is an important criterion.
- For this test, the valve shall be assembled with the positioner. Packing shall be tightened as required for the intended service conditions or the hydrostatic test.
- Acceptable maximum dead band for valves without positioners shall be 4 percent with an expected range of 2 to 4 percent. For control valves with positioners, the maximum acceptable dead band shall be as per Table I.
- The maximum allowable dead time Td of the control valve assembly for any step change in the range of 2 to 5 percent of the full travel is given in Table II.
- The maximum allowable Step Response Time T86 of the control valve assembly for any step change in the range of 2 to 5 percent of valve full travel should be as per Table III, unless a faster step response time is specified in the specification sheet.
