تبلیغات
انسانم آرزوست... - برق3
انسانم آرزوست...
*من همچنان عینکی زده ام که شیشه ندارد*مدام به آن ، ها میکنم تا پاک شود * غافل از آنکه چشمانم غبار آلود است نه عینکم*
گروه طراحی قالب من
درباره وبلاگ


مبهم وشاید کمی پیچیده
.
.
.

این همه آن چیزیست که در سرزمین جاوید انتظارش را میکشیم...


مدیر وبلاگ : pc7a
نویسندگان
45
material does not come into contact with the test point and that a minimum of 30 mm clearance between the reinforcement and the test point shall be maintained.
9.4.3.4 Test points shall be installed as required, but will be located midway between sacrificial anodes.
9.4.3.5 Connections of test lead wires to pipelines above water must be installed so as to be mechanically secure and electrically conductive. Pipe and test lead wires shall be clean, dry, free of foreign material and properly coated.
9.4.3.6 Conductive connections to other pipelines or across electrical isolating devices shall be mechanically secure, electrically conductive and suitably coated. Bond connections shall be accessible for testing.
9.4.4 Reinforcement
9.4.4.1 Pipeline weight coating reinforcement material shall be carefully installed in accordance with standard specification of IPS-C-TP-274.
9.4.4.2 Each pipeline section shall be inspected and tested using a 1000 Volt insulation test set to ensure that the reinforcement is not in contact with the pipe wall. A minimum reading of 1 M ohm will be regarded as satisfactory.
9.4.4.3 After each joint has been completed the pipeline section reinforcement shall be insulation tested from the remote end, this will be applicable for both lay barged and bottom pull pipelines.
9.4.5 Pipeline crossings
9.4.5.1 Where two or more pipeline crosses, test points shall be fitted to the pipeline and positioned to coincide with the crossing.
9.4.5.2 Where test points for bonding purposes have not been installed, a clamp arrangement with set screw shall be utilized. Care shall be taken not to damage the coating and the pipeline. The set screw shall be tightened only sufficiently to make a good electrical contact but not to damage the pipe wall.
10. ELECTRICAL MEASUREMENTS AND TESTS
10.1 General
10.1.1 This Clause 10 indicates the apparatus needed and the techniques for measuring voltage, current and resistance, and testing for continuity of structures to ensure the successful commissioning of a cathodic protection installation. Some survey techniques are described.
10.1.2 Electrical measurements and inspections are necessary to ensure that initial protection of the structure has been established in accordance with applicable criteria, and that each part of the cathodic protection system is operating satisfactorily.
It is important for subsequent system checks to be carried out to ensure that the structure remains protected and, if changes are noted, that action is taken to return the system to a protected condition.
Whenever the surface of a structure is exposed, the condition of the coating shall be noted, and the coating repaired appropriately.
10.1.3 It shall be the responsibility of the contractor to perform all precommissioning and commissioning checks on the cathodic protection systems as outlined in this Construction standard.
10.1.4 It shall be the responsibility of the contractor to supply all test equipment to perform the tests outlined in this Construction standard.
10.1.5 All tests performed by the contractor will be witnessed by and shall be completed to the satisfaction of the Company.
Dec. 1997 IPS-C-TP-820
46
10.1.6 The contractor shall carry out and document all tests under the supervision of the Company representative.
10.1.7 The inspection and testing shall not cause danger to persons or livestock and shall not cause damage to property and equipment.
10.1.8 Under no circumstances shall any cathodic protection system be energized before inspection and testing is completed.
10.1.9 The stages at which these tests are carried out on particular installations are indicated in the appropriate clauses.
10.1.10 Tests for corrosion interaction interferences are dealt with in Appendix A.
10.2 Potential Measurements
10.2.1 Instruments
10.2.1.1 The meters and equipment used for potential survey and testing are described in 7.1.3 and Appendix A of IPS-I-TP-820.
10.2.1.2 All instruments used for determining electrical values shall be of an appropriate type and be of the required accuracy. They shall be maintained in good working condition at all times.
10.2.1.3 Where fluctuations in the electrical measurements are noted, it may be necessary to substitute recording instruments for meters during surveys.
10.2.1.4 Electrodes other than copper/copper sulfate and silver/silver chloride may be used, provided that their relationship with these electrodes is either known or established prior to each measurement (see IPS-I-TP-820).
10.2.2 Potential survey of buried structures
For methods of survey reference is made to 7.2 of IPS-I-TP-820.
10.2.3 Potential survey of offshore structures
For methods of survey reference is made to 7.4 of IPS-I-TP-820.
10.2.4 Potential survey of internal protection of plant
10.2.4.1 General
With fully enclosed plant, it is normally necessary to install permanent measuring points or reference electrodes. Where the positions at which measurement should be made can be predicted, these facilities are preferably installed before commissioning.
Alternatively, potential surveys can be carried out (see 10.7.4) initially with temporary equipment to determine the positions where the potentials are most positive and whether the most negative potentials are acceptable.
10.2.4.2 Permanently-installed reference electrodes
The most convenient method of mounting reference electrodes inside plant is by means of a ’screw-in’ assembly such that the electrode can easily be withdrawn for inspection and replacement of either the entire unit or the electrode material.
The electrodes can be wired to central monitoring and control equipment. A disadvantage lies in the difficulty of checking the accuracy of the electrodes, once installed.
Dec. 1997 IPS-C-TP-820
47
For detailed potential surveys, or if it is impossible to use ’screw-in’ mountings, reference electrodes can be attached by suitable non-metallic fixings to the protected surface and the insulated connecting leads brought out through the plant wall through a suitable gland.
Generally, it is advisable to install at least one reference electrode for each cathodically-protected compartment. The reference electrode should be installed at the position where corrosion is most likely, e.g. at junctions of ferrous and non-ferrous materials and/or remote from anodes.
10.3 Direct Current Measurement
The methods of testing for current measurements are described in B.4 of IPS-I-TP-820.
10.4 Resistance Measurement
10.4.1 Soil resistivity measurements
(See Appendix B).
10.4.2 Earth electrode resistance measurements
The necessary method of testing are described in Appendix C.
10.4.3 Determination of bond resistance
Where it is necessary to determine the value of the resistance which should be connected in series with a bond, to adjust the structure electrolyte potential of a structure to a desired value. It can be done either by inserting a series of fixed calibrated resistors until a suitable value is found, or adjustment can be made by using a variable resistor, the resistance of which is subsequently measured. Alternatively, if the galvanometer shown in Fig. 1 is calibrated to indicate voltage, the desired potential conditions on the structure can be obtained by adjustment of the resistor. The necessary resistance value is determined as the ratio of the voltage to the current. This arrangement has the advantage of obviating the need for low resistance leads. Special milliohm meters are also available for measuring the very low resistance of bonds.
10.4.4 Continuity of structure
The method of testing are described in B.12 of IPS-I-TP-820.
10.5 Field Testing of Electrical Isolating Equipment
For methods of testing refer to B.1 of IPS-I-TP-820.
Dec. 1997 IPS-C-TP-820
48
ZERO RESISTANCE AMMETER CIRCUIT USED TO MEASURE CURRENT FLOWING IN A BOND (BOND DISCONNECTED)
Fig. 1
Note:
With current Ib adjusted to give no deflection on the galvanometer Ib is equal to the bond current.
10.6 Tests Prior to Installation of Cathodic Protection on Buried or Immersed Structures
10.6.1 Soil resistivity
(See Appendix B).
10.6.2 Soil/water evaluation
10.6.2.1 Soil/water sampling
- Soil samples may be obtained from along the pipeline route with a minimum of one sample from each type of soil noted to exist. Samples are to be ideally between 250 g and 2,000 g and placed in sealed, sterile, air tight containers and should fill the containers completely.
- Where bacteriological analysis is to be undertaken, the soil sample is to be as little disturbed as possible and completely fill the containers.
- Soil samples are obtained from depth either by excavation or by auguring techniques.
- Water samples may be obtained from river, estuaries and water logged locations. Samples need to be ideally between 1 and 2 liters, placed in sealed, sterile, air tight containers and fill the containers completely.
- In the case of immersed structures, any analysis of water samples shall include measurement of the oxygen content and conductivity. It should be noted that, particularly in the case of estuarine waters, considerable variation can occur according to the state of the tide and also according to the season. Moreover, stratification is often present and the use of a suitable sampling technique is recommended.
- The analysis is to be completed with the minimum of delay from time of sampling.
Dec. 1997 IPS-C-TP-820
49
10.6.2.2 pH measurements
- After resistivity measurements, pH is perhaps the most widely used test for corrosivity. Where corrosion could be caused or enhanced by chemical attack, the pH measurement may be used to assess this risk.
- The methods available for pH measurement include:
- glass electrode and millivoltmeter;
- colorimetric;
- indicator papers.
- Glass electrodes may be used with either potentiometric or high impedance millivoltmeters. Both types are available as portable, battery-powered units for field use. Apparatus, reagents and procedures are listed in both ASTM G51 and BS 1377.
- Colorimetric techniques are also described in BS 1377 and may be used as rapid field techniques. However, results can be erratic and excessive turbidity in the soil may mask end point.
- Indicator papers are a practical site method and are sufficiently accurate for most survey purposes. Dry soils may be wetted with de-ionized water for this technique.
10.6.2.3 Soluble salts
Chemical analysis for salts is usually restricted to chlorides, sulphates, carbonates and sulphides. The latter two being analyzed qualitatively and chlorides and sulphates analyzed quantitatively. Quantitative analysis of chlorides and sulphates is undertaken by gravimetric, volumetric or colorimetric (semi-quantitative) analysis. The gravimetric and volumetric analysis of sulphates is detailed in BS 1881. For corrosion purposes, only the water-soluble sulphates are of concern, rather than total sulphates.
- A quick assessment of resistivity of water may be made from the value of total dissolved solids by the following formula: m-ohmin y ResistivitSolidsDissolved Total250,6=
10.6.2.4 Bacterial analysis
There are a number of micro organisms which thrive in or create conditions conductive to corrosion. These principle organisms are supho bacteria, ferri bacteria and sulphate reducing bacteria. In soils the most common form of bacterial corrosion is caused by sulphate reducing bacteria. These bacteria are most active in anaerobic soils when the hydrogen ion concentration is near neutral, pH 7.0, but are known to grow in the range pH 5.5 to 8.5. In their action they convert sulphates in the soil to sulphides.
Various approaches exist to detect soils in which sulphate reducing bacteria are likely to thrive. They are:
- Redox potential
Redox potentials are measured in the field by measuring the potential of a platinum electrode using a calomel reference (see Appendix E). The reading is pH corrected.
The general accepted criteria for microbial corrosiveness as quoted in BS 7361 are:
Redox potential 100 mV severe
corrected to pH7 100-200 mV moderate
(mV Standard 200-400 mV slight
Hydrogen Electrode) 400 mV non-corrosive
This technique is probably the most widely used for assessing microbial activity. Reproducibility of results is, however, poor and the equipment can only be used with confidence in relatively soft soils.
- Detection and Enumeration
Detection of sulphate reducing bacteria is undertaken by using one of a number of culture media which includes Bars, Postgate and API media. Generally, the culture consists of a
Dec. 1997 IPS-C-TP-820
50
nutrient, an indicator and a redox poising agent with the pH adjusted to near neutral.
Enumeration is carried out by using a series dilution. After solidification of the culture medium and 2 day incubation, the colonies of bacteria can be counted.
- Chemical Tests
These basically cover sulphate content, organic materials content, soluble iron and hydrogen uptake of the soil.
10.6.2.5 Moisture content
Moisture content of soils may be determined by one of the methods described in BS 1377.
10.6.3 Structure/electrolyte "natural" potential survey
The structure/electrolyte potential survey shall be carried out to determine the structure/electrolyte potential variation along, or over the surface of the structure (see 10.2).
Such a set of potential measurements may indicate those points on the structure where the worst corrosion is likely to be taking place.
With no applied cathodic protection, and in the absence of stray currents, the most negative structure electrolyte potentials indicate the corroding areas. On the other hand, if corrosion is due predominantly to stray current in the soil, the more intense corrosion will be associated with the more positive structure/electrolyte potentials.
10.6.4 Stray electric currents
Where the presence of stray electric currents is suspected, e.g. in proximity to d.c. electric traction systems or where varying structure/electrolyte potentials indicate the possibility of such currents, it is necessary to determine more accurately the extent of stray current effect on the structure. This can be done by plotting the potential field in the area, using a stationary reference electrode, or a structure, as a reference point.
The necessary methods of testing are described in Clauses 11 and B.11 of IPS-I-TP-820.
10.6.5 Tests for electrical continuity
Tests shall be carried out whenever the continuity of the structure is in doubt, to locate any discontinuities in accordance with Clause 8.4 and B.12 of IPS-I-TP-820.
10.7 Tests During the Commissioning Period
10.7.1 General
The structure/electrolyte potentials at various points on a structure will continue to change for some time after protection has been applied. Tests shall, therefore, be made at intervals and currents adjusted as necessary until conditions become stable with potentials at all points not less negative than the values given in protection criteria (refer to Clause 6 of IPSI- TP-820).
A comprehensive survey shall then be made and the results analyzed to provide a list of conveniently carried out tests by which the continued satisfactory operation of the protection system can be confirmed.
Immediate action shall be taken if abnormally positive changes in potential occur, particularly at the point(s) of application of current indicating that one or more transformer-rectifiers have been reversed.
More frequent inspections (for example at monthly intervals) are recommended where:
a) the non-operation of one transformer-rectifier would result in a total or partial loss of
Dec. 1997 IPS-C-TP-820
51
protection;
b) the non-operation of the transformer-rectifiers is likely, due to factors outside the operators control, e.g. known unreliable power supplies, joint operation with a third party, susceptibility to electrical storms; or
c) protection is provided by a single bond from another protected structure.
It is important that commissioning and routine test readings shall be permanently recorded. In many instances, comparison with these provides the only information that is available as to the condition and performance of the system. To this end, a routine shall be established for the periodic review of the measurements to ensure that the conditions are satisfactory. Consideration shall be given to the computerization and graphical presentation of records, with the inclusion of exception reporting for test measurements that fall outside set limits.
10.7.2 Buried structures
Structure/electrolyte potentials shall be measured at a series of points including, particularly, points remote from the groundbed or anode positions.
Outputs shall be adjusted to the minimum that gives the desired level of protection.
The period required for the potentials to become stable may vary from a few days for a well-coated structure, to a few months for a bare or poorly coated structure.
Where possible, currents from individual sacrificial anodes or transformer-rectifier units shall be measured. In the case of a complicated pipe system, it is also useful to measure the current flowing from individual branches or sections.
Once the operating conditions have been established, organizations that might be installing underground equipment in the area in the future shall be given sufficient information for them to be aware of possible interaction problems. This will include, for example, groundbed positions and expected currents, and , if not already provided, and indication of the routes of the protected structure and of any structures that have been bonded to it to reduce interaction.
10.7.3 Fixed immersed structures
Structure/electrolyte potentials shall be measured, at the points provided, soon after the protection is switched on. Individual (or group) anode currents shall be measured and adjusted to the minimum that gives protection.
The structure potential shall be measured by connecting a high input-impedance voltmeter (at least 1 M.) to the structure, usually at a test point, and placing a reference electrode, connected to the positive terminal of the voltmeter, as near as practicable to the immersed surface of the structure (see Fig. 3).
Because accurate measurement of the structure potential requires the reference to be located at the surface of the structure, the reference electrode may be located by a diver, a remotely operated vehicle or be permanently installed at various areas of the structure (such as areas of complex geometry or where shielding can occur). Such readings can then be related to readings taken with a reference electrode placed adjacent to the side of the structure.
Care shall be taken to ensure that the structure component to which the measuring voltmeter is connected is not carrying a substantial cathodic protection current. With impressed current systems, in particular, parts of the structure may be carrying a large current and hence may cause a significant voltage drop error in the measurement.
10.7.4 Internal protection of plant
Structure/electrolyte potentials shall be measured at the test points before and soon after the installation is switched on (see Fig. 4). The currents at individual anodes (or groups of anodes) shall be monitored and adjusted as necessary after a further period, e.g. one week, then, if no serious departure is observed, again after one month. At each adjustment, the individual and total anode
Dec. 1997 IPS-C-TP-820
52
currents shall be noted for reference.
Each sensing electrode used for automatic control shall be checked against a suitable reference electrode installed close to it. Unless there is experience with similar plant, reference electrodes shall also be installed at a sufficient number of positions in the protected equipment to enable a representative potential distribution curve to be plotted. This will show whether the position of the sensing electrode was chosen judiciously and whether the correct control setting has been selected. If more than one sensing electrode provides the feedback signal to the controller, the readings on each shall be compared for incompatibilities before and after switching on the protection. Readings may show differences due to the presence of electropositive materials, and the gradients around anodes. Ideally, all the sensing signals shall be within 50 mV when the protection is switched on. Slightly wider tolerances (e.g. 100 mV) may still form an acceptable basis for control.
10.7.5 Internal surfaces
The structure potential shall be measured by connecting the positive terminal of a high-impedance voltmeter (at least 1 megohm) to the structure, usually at a test point. The negative terminal shall be connected to a reference cell which is positioned as near as practicable to the immersed surface of the structure. (see Fig. 5).
Because accurate measurement of the structure potential requires the reference to be located at the surface of the structure, the reference electrode may be carried by a remotely operated vehicle or be permanently installed at various areas of the structure (such as areas of complex geometry or where shielding can occur). Accurate readings of the structure potential can then be related to readings taken with a reference electrode placed adjacent to the side of the structure.
Care shall be taken to ensure that the structure component to which the measuring voltmeter is connected is not carrying a substantial cathodic protection current. With impressed current systems, in particular, parts of the structure may be carrying a large current and hence may cause a significant voltage drop error in the measurement.
10.8 Specialized Surveys
There are a number of specialized survey techniques being utilized to provide additional detailed data concerning corrosion prevention systems.
These techniques would normally be carried out by specially trained personnel using purpose-built equipment and instrumentation, often only available from specialist contractors. These surveys are generally time-consuming but the information gained may not be available from other methods.
The surveys covered by this Standard are:
1) Surveys for detecting external pipeline coating defects, i.e.:
- Pearson survey.*
- Electromagnetic current attenuation survey.*
- Close interval pipe to soil potential survey.*
2) Surveys to determine the effectiveness of cathodic protection systems, i.e.:
- Close interval pipe to soil potential survey.*
- Current drainage survey. (See Appendix D).
* For the methods of above surveys see Appendix B of IPS-I-TP-820.
Dec. 1997 IPS-C-TP-820
53
MEASUREMENT OF STRUCTURE POTENTIAL ON FIXED IMMERSED STRUCTURES
Fig. 3
Dec. 1997 IPS-C-TP-820
54
ALTERNATIVE METHODS FOR MEASURING STRUCTURE POTENTIALS
Fig. 4
Note:
1) Method A employs a portable reference electrode.
2) Method B employs a permanent reference electrode.
Dec. 1997 IPS-C-TP-820
55
Notes:
1) Method A employs a portable reference electrode.
2) Method B employs a permanent reference electrode.
3) The polarity shown is for digital, off-set zero and center-zero voltmeters.
When using direct reading voltmeters the test leads need to be reversed to obtain negative potential readings.
ALTERNATIVE METHODS FOR MEASURING INTERNAL STRUCTURE POTENTIALS
Fig. 5
PIPE-TO-SOIL POTENTIAL DISTRIBUTION ON WELL-COATED
AND BADLY COATED PIPELINES
Dec. 1997 IPS-C-TP-820
56
Dec. 1997 IPS-C-TP-820
57
11. COMMISSIONING OF CATHODIC PROTECTION SYSTEMS
11.1 Introduction
11.1.1 This Clause 11 indicates the stages at which tests shall be made for commissioning of cathodic protection systems for buried and immersed structures, tanks, and internally-protected plant.
11.1.2 The relevant test instruments and the techniques for their use are described in IPS-I-TP-820.
11.1.3 The effectiveness of a cathodic protection installation depends on applying and maintaining the correct potential difference between the structure and the adjacent environment at all parts of the structure. This is the objective of the procedures described in this Section. The criteria for cathodic protection shall be in accordance with Clause 6 of IPS-E-TP-820.
11.1.4 The contractor shall ensure that the check-out and commissioning procedures are sufficient to demonstrate that the cathodic protection system installation satisfies the criteria established by the Company project tender documents and the associated company specifications and drawings.
11.2 Precommissioning Inspection and Check
11.2.1 Every cathodic protection installation shall be inspected and tested by contractor before commissioning test, this is to ensure as far as practicable that all the requirements of the contract has been carried out and installation is ready for precommissioning. The contract requires that the test carried out shall not in any way be a danger to persons, property or equipment.
11.2.2 The Engineer is entitled to inspect, examine and test the workmanship during the course of installation; any such inspection shall not release the contractor from his obligation under the contract. Any work in the opinion of the Engineer which is not up to standard shall be rectified at the contractor own expense.
11.2.3 A program shall be provided for precommissioning test with the approval of Engineer.
11.2.4 All provision such as testing equipment, special tools and coordination for availability of power and all pertinent work permit shall be envisaged.
11.2.5 The written programs for check-out and commissioning, including detailed check sheets, shall be submitted 45 days prior to the scheduled date for beginning check-out and commissioning activity.
11.2.6 The Company-approved design drawings and specifications shall form the basis for the construction of the cathodic protection system.
11.2.7 In addition to these drawings, the Company will furnish the Vendor drawings for all company-supplied equipment. The contractor shall furnish the vendor drawings for all equipment supplied by the Contractor.
11.2.8 The Contractor shall make as-built corrections to both the Company supplied and contractor-supplied drawings, including all changes required during check-out and commissioning.
11.2.9 Detailed check sheets shall be developed as part of the check-out and commissioning procedure prepared by the Contractor. The check sheets shall have provisions for certifying that the various individual equipment items are properly installed in compliance with the specified performance and safety requirements and are suitable for operation.
11.2.10 The detailed check sheets shall be standardized for each type of CP systems and shall contain as a minimum:
- Checks and tests conducted.
- Record of test results.
- Acceptance signatures.
- Equipment tag number.
11.2.11 The contractor, in collaboration with the engineer, shall carry out all precommissioning
Dec. 1997 IPS-C-TP-820
58
checks of the completed system. Duties in this connection, consist of, but are not limited to the following:
- Transformer/rectifiers
The contractor shall check the transformer/rectifier units for correct polarity, supply voltage, fuse rating, and full load test. The contractor shall endeavor to keep the time for full load test as minimum as possible. In addition, the testing of the transformer/rectifiers shall be carried out to ensure adequate electrical connection and that no damage has occurred during installation.
- Groundbed
Groundbed resistance test shall be made as soon as the groundbed is installed and backfilled, under the supervision of the Engineer.
- Cable test
The Contractor shall ensure adequate care is taken during installation and backfill to prevent damage to the wiring insulation and shall test the wiring, after backfilling, for continuity, with a low voltage test. The method and results shall be approved by the Engineer.
- Insulating joints
After the hydrostatic test and before gas commissioning, the contractor shall make an electrical test to verify the insulation of the joint. The minimum value shall not be less than one thousand (1000) ohms.
After commissioning, the effectiveness of the insulation shall be tested by Cathodic Protection Impressed Current. In this test, the current will be drained from one side of the insulating joint to the extent that a negative swing of potential of 400 mV is maintained. In this case, insulating joint is accepted if the potential on the unprotected side of the joint remains natural or becomes more positive. Insulating joints found defective after installation shall be replaced by the contractor at his expense.
- Cased crossing
Test on cased crossings shall be made in accordance with B.1 of IPS-I-TP-820.
During commissioning of the cathodic protection system, tests on the casing insulation will be conducted again by draining cathodic protection current in such a way that a minimum negative swing of 400 mV is achieved on the carrier pipe. In this case, the insulation shall be effective if the potential of the casing shifts towards positive.
Results of the above tests shall be approved by the Engineer. All the foregoing tests and remedies of work shall be at the contractor’s expense.
- Test stations (test points)
All installations shall be subject to test during construction and on completion of the work. Should any test point prove faulty or damaged in construction and/or installation, the contractor shall rectify the defect(s) as soon as discovered and/or instructed by the engineer.
- Earthing system
Check completed earthing system for continuity of main earthing system loop and continuity of all taps to equipment.
Check earthing system using a megger earthing resistance tester or the type which balances out the reference grounds.
Dec. 1997 IPS-C-TP-820
59
Earthing resistance values in all of the above tests shall be 5 ohms or less. If greater than 5 ohms, supplemental ground rods shall be installed until an acceptable value is obtained.
11.3 Hook-up and Commissioning
11.3.1 General
11.3.1.1 All work shall be executed in strict accordance with the Company-approved drawings and specifications. The written approval of the Company representative is required for any deviations by the contractor from these drawings and specifications.
11.3.1.2 The contractor shall bring to the attention of the Company representative any areas of the drawings and/or specifications which conflict or do not meet safe and acceptable practices.
11.3.1.3 The Contractor shall be responsible for the protection and security of all materials and equipment during all stages of commissioning.
11.3.1.4 The Contractor shall not perform any tests that would either void the Vendor warranty or damage the materials and equipment.
11.3.1.5 The Contractor shall tie-in the ac power source to the rectifier(s) with all work carried out by qualified electricians.
11.3.1.6 The Contractor shall be responsible for all aspects of the system(s) start-up.
11.3.1.7 An "Adjustive Survey" shall be provided to the Company within thirty (30) days of system start-up.
11.3.1.8 The Contractor shall submit with the "Adjustive Survey" the following additional documentation on cathodic protection system(s):
a) Copies of accurately dimensioned "As-Built" drawings of all installations.
b) Copies of operating and maintenance manuals for all equipment provided and installed by the Contractor.
The above information, when available shall be incorporated in the plant data books.
11.3.1.9 Written programs for commissioning of CP system shall be developed by the contractor. These programs shall include detailed check sheets and shall be submitted for acceptance to the Company at least 45 days prior to the scheduled commencement of the check-out and commissioning activity.
11.3.1.10 The commissioning program shall detail the final tests to be conducted on all equipment after the check-out program is complete. The commissioning program shall demonstrate the proper operation of the complete CP system.
11.3.1.11 All check-out and commissioning shall be witnessed by the Company representative.
11.3.1.12 Check-out tests may be conducted concurrently with commissioning tests.
11.3.1.13 The Contractor shall submit a full report to the Company at completion of commissioning (see 11.5).
11.3.2 Impressed current systems
11.3.2.1 After completion of the installation, check-out, inspection and testing of the cathodic protection equipment, it is necessary to carry out the following procedures.
11.3.2.2 Prior to energization of the cathodic protection systems, the contractor shall carry out a natural potential survey all along the length of structure under protection at all test points and current drainage points.
11.3.2.3 The transformer/rectifiers then shall be energized for a minimum period of 72 hours before any measurements are taken.
Dec. 1997 IPS-C-TP-820
60
11.3.2.4 The contractor shall adjust the current by steps to limit the drain point potential according to the criteria for the steel under protection (refer to Clause 6 of IPS-I-TP-820).
11.3.2.5 During the polarization period with impressed-current systems, regular checks of structure potential and transformer-rectifier output shall be made in order to avoid gross over-protection.
11.3.2.6 The frequency of subsequent T/R readings depends on the reliability of the power supply. Readings taken once per fortnight are often chosen to start with.
11.3.2.7 During the polarization period the current output of the transformer-rectifiers shall be progressively reduced to maintain the steel-to-soil potential at its desired level.
11.3.2.8 Once all the transformer/rectifiers have been energized, applied potentials shall then be taken at the same location as for the natural potentials.
11.3.2.9 Should the interphase potential between two groundbed installations be higher than the minimum criteria laid down, this usually being 0.95 Volts, the drain point potential should then be adjusted to a lower potential to prevent wasteful losses of power at the installations.
11.3.2.10 Particularly in high-resistivity soils voltage drop through the soil as a result of applied current for cathodic protection can be considerable. As a result the potentials measured on the surface over the pipe whilst the current is ’on’ will not reflect the potential at the pipe surface.
11.3.2.11 In order to measure a more true potential the current shall be switched off momentarily, the potential (the ’off’ potential) shall be measured immediately after interruption (within seconds). This potential is not affected by any voltage drop in the soil. Transformer-rectifiers should be equipped with automatic and synchronizable interrupters for this purpose.
11.3.2.12 It is necessary to repeat this test after polarization has taken place, approximately 14 days. This may require further adjustments of the current output of the transformer/rectifier to keep the applied potentials between the minimums and maximums laid down.
Notes:
1) Besides, the detailed information related to the design, construction and commissioning of the installation, records shall be kept of current outputs and protective potentials. The data shall be analyzed after each survey and corrective action taken soonest but within one month. Whenever a cathodic protection system is installed the necessary instruments shall be purchased to enable the engineer-in-charge to make the required measurements.
2) After a protective current has been applied by an impressed-current cathodic protection system polarization of the protected structure occurs, causing a gradual fall in current requirements. The rate at which polarization occurs depends on the nature of the medium surrounding the structure and on the current density; the time elapsing before the current requirement falls to a steady value while maintaining the structure at the desired potential may vary from a few days to many months.
3) The reference electrode shall be located in contact with the surface of the earth directly over or not more than five or six pipe diameters away from the structure along the surface of the earth at selected locations as indicated on the drawings. When measuring the potential of a tank, the reference shall be placed a half tank diameter away from the structure.
4) Variable resistors shall be installed in the negative drain circuit, if required, to balance the current to each of the adjacent pipelines. Each negative circuit shall be provided with a suitably sized shunt and diode at the DC source. The installation of the diode is required to prevent mutual influence of pipelines during "on-off" surveys.
11.3.3 Sacrificial anodes
11.3.3.1 During the polarization period, regular checking of potentials shall be carried out to obtain early warning in case the system is inadequate.
11.3.3.2 The potential of the protected structure can never become more negative than the anode potential itself. The latter is usually well within the range of acceptability.
Dec. 1997 IPS-C-TP-820
61
11.3.3.3 Current output from the anodes is self-regulating since with further depressed potentials of the structure, the driving force between anode and cathode becomes smaller. This automatically results in a lower current drain. Calculation will show that zinc and aluminum anodes can provide approximately twice the design current at the very start of the polarization period, with the advancement of the polarization the current gradually reaches the equilibrium state (which could be lower than the design current drain).
11.3.3.4 The sacrificial anode system usually comprises 2 cables connected to the structure, one for measuring the applied potential and the other to be connected through a terminal panel and a removable link to the sacrificial anode. The removable link is maintained for the measurement of current between the anode and the structure. A sensitive milliammeter with a very low internal resistance is connected between the terminals after the link has been removed and a measurement of the current output is taken. This measurement shall be taken as quickly as possible to prevent depolarization between the anode and the structure since increased current will be required should the structure depolarize.
11.3.3.5 With anodes used suspended under water and accessible, an indication of the probable remaining life can be obtained by periodic lifting and weighing. A comparison of the rate of wastage will also show the extent to which individual anodes are contributing to the protective system.
11.3.3.6 When sacrificial anodes are used to protect condenser end-plates, box coolers, and similar equipment, visual inspection together with potential measurements provide a method of checking.
11.3.4 Interference
11.3.4.1 The application of cathodic protection with impressed current to a buried or immersed structure (referred to as the primary structure) causes direct current to flow in the earth or water in its vicinity. Part of the protection current traverses nearby buried or immersed pipes, cables, jetties or similar structures alongside (termed secondary structures), which may be unprotected and the corrosion rate on these structures may, therefore, increase at points where the current leaves them to return to the primary structure.
11.3.4.2 Interference with other buried or immersed installations shall be measured by the contractor in the presence of the Engineer and, the owners of the foreign structures, after switching-on the Impressed Current Cathodic Protection System (see Appendix A).
11.3.4.3 The Contractor shall conduct the tests according to the methods described in Appendix A with the understanding that the criterion is the swing of the potential of the foreign structure from the natural value. The test procedure is detailed hereunder:
a) The foreign structure-to-electrolyte potential shall be taken while the transformer-rectifier is turned-off.
b) Structure-to-electrolyte potential shall be taken while the transformer-rectifier is "on position".
c) Several readings shall be made by the contractor for comparison.
11.3.4.4 The maximum positive swing of potential at any part of foreign structure resulting from interference shall not exceed 20 mV and, in case of interference exceeding a positive change of 20 mV, the Contractor shall carry out the remedial works described in Appendix A.
11.4 Commissioning Survey
The commissioning survey shall include the following tests and measurements, where applicable, to ensure that the structure is protected in accordance with the design criteria, and that all equipment is correctly installed and functioning correctly:
a) Measurement of structure potential at all test points, both before and after energization of the cathodic protection system.
Notes:
1) Following the application of cathodic protection, the potential level of the structure will
Dec. 1997 IPS-C-TP-820
62
change with time owing to polarization and, to ensure the structure potential is in the desired range, it may be necessary to take several potential measurements over a given time.
2) Systems requiring large currents may need to be briefly de-energized to permit potential measurement free of voltage drop error.
3) In tanks containing fluids of relatively high resistivity, it is recommended that "off" potentials are measured to minimize voltage gradient errors for impressed current systems.
b) A check for correctness of polarity of electrical circuits, i.e. positive to anode and negative to structure.
c) A functional test of all test points, to ensure correct installation/operation.
d) Assessment of the effectiveness of the following items:
i) All insulating devices.
ii) The continuity of bonds.
iii) The isolation of the structure from electrical earths and secondary structures in accordance with the design.
iv) Casing insulation.
v) Stray current control equipment.
vi) Structure earthing:
A) fortuitous;
B) deliberate; and
C) alternating current.
e) Measurement of the coating resistance.
f) A check that the anode current distribution is as desired.
g) For impressed current systems, the measurement of back e.m.f. and loop resistance.
h) The current required to provide protection.
i) The voltage output of the impressed current system.
j) A test for interference current flow in bonds.
The survey shall also identify the following:
i) The variation in output current and structure potential with time. The rectifier output voltage may also be recorded.
ii) Locations where future measurements (current, source voltage, structure/electrolyte potential) can be taken to provide a representative view of the operation of the system.
iii) Need for any additional test points or cathodic protection facilities.
Data from the survey shall be recorded and retained for future reference.
Details of tests and testing methods to be carried out during the commissioning periods are given in Section 10. The sequence of tests shall be commenced as soon as possible after commissioning.
11.5 Commissioning Report
The Contractor shall submit a commissioning report to the Company representative at the conclusion of check-out and commissioning.
Dec. 1997 IPS-C-TP-820
63
Records associated with cathodic protection systems shall be kept as historical data for future consideration and action. Records are used to demonstrate that a cathodic protection system is working.
The commissioning report shall include, but does not need to be limited to the following:
a) Design documentation.
b) Results of periodic survey checks.
c) Results of equipment checks.
d) Agreements made with owners of foreign structures.
e) Location of any test points added to the system.
f) Coating materials and application procedures.
g) Correspondence with regulatory authorities.
h) Information on and location of stray current facilities connected.
i) Commissioning objectives.
j) Description of CP system operation.
k) Original of all check sheets and discrepancy lists.
l) Conclusions and recommendations.
12. INSTALLATION OF ELECTRICAL ISOLATION EQUIPMENT
12.1 Introduction
This Clause 12 deals with the procedures to be used when installing the equipment used for electrically isolating pipelines. The procedures are designed to ensure that:
12.1.1 A satisfactory degree of electrical isolation is achieved at the time of installation and that the joint is not damaged so as to cause an accelerated degradation rate with time.
12.1.2 The installed equipment is adequately protected against the effects of stray dc or induced ac voltages.
12.1.3 There is adequate provision for test leads to allow for field testing and maintenance. Typical arrangements are shown in Fig. 6.
12.1.4 Isolation joints installed at coating/electrolyte changes shall always be bonded in test points, to keep the pipeline electrically continuous when the cathodic protection is operational.
12.1.5 If cathodic protection is to be applied on non-welded pipelines the continuity of the pipeline shall be ensured. This should be done by the installation of permanent bonds over high resistance flanges/couplings, using cables and approved attachment methods.
12.1.6 The continuity of non-welded pipelines shall be checked, e.g. by carrying out overlapping potential measurements.
Notes:
1) The buried insulating joints installed on pipelines are occasionally used to open the electric continuity of the pipelines and thus create sections isolated from the rest of the network, when it is desired to:
- measure the electric resistance of pipeline coating;
- locate pipeline coating defects;
- limit the zone of influence of the impressed current systems.
Dec. 1997 IPS-C-TP-820
64
2) The normal state of buried insulating joints installed on pipelines is to be electrically shunted.
The aboveground insulating joints installed on district regulators and service lines must never be shunted. Such aboveground insulating joints are not part of the cathodic protection installations; they are rather part of the passive protection.
12.2 Installation
12.2.1 General
12.2.1.1 When installed, all equipment items shall be properly supported and aligned so that any forces transferred from adjoining pipe are minimized. This should be considered when equipment locations are selected. The type of equipment chosen shall be suitable for the mechanical forces to be encountered at the chosen site. Isolating devices should not be installed in gas systems at locations where there is likelihood of internal moisture accumulation. When possible, the electrical resistance should be checked immediately before and after installation.
12.2.1.2 Before any work is carried out on or near an isolated flange, the area shall be checked for hazardous atmospheres.
12.2.1.3 To avoid risk of electric shock and the possibility of sparking, it is advisable that insulating joints be crossbonded before being assembled. This precaution is essential for hydrocarbon product lines.
12.2.2 Insulating joints
12.2.2.1 Insulating joints shall be ordered with the weld end preparation conforming to the main pipe laying specifications. The manufacturer’s special instructions for installation shall always be followed, particularly when welding in joints with short overall lengths, to ensure that the heat generated does not damage the insulating materials used in the joint construction.
12.2.2.2 The Contractor shall align, install and test insulating joints shown in the drawings. The testing shall include:
- electrical test to verify the insulating of the joint1;
- hydrostatic test in-situ, with the pipeline.
12.2.2.3 The Contractor shall perform this work with proper caution so as not to damage the insulating material during the handling, welding and pipe laying.
12.2.2.4 In no case shall the Contractor carry out welding in the vicinity of an insulating joint without shunting the insulation joint. The shunt shall be removed by the Contractor upon completion of the welding.
12.2.2.5 When welding the joint into the pipeline, the Contractor shall take care to ensure that heat shall not be conducted along the pipe and cause damage to the internal lining or insulation.
12.2.2.6 The buried insulating joint shall be manually coated as soon as possible after installation, as specified in design specification. The above-ground insulating joints shall be painted as specified in design specification.
1 The resistance across isolating joints shall be measured immediately before welding into the pipeline. The minimum resistance shall be 1 mega ohm (106 ohm).
12.2.3 Isolated flange joints
12.2.3.1 Factory pre-assembled types
These are supplied with weld ends and may be installed as described in Subclause 12.2.1.
Dec. 1997 IPS-C-TP-820
65
12.2.3.2 Flange insulation kits
12.2.3.2.1 The assembly of an insulating flange requires particular care to ensure that insulation is not lost due to mechanical failure of the components. Flanges are welded to the pipeline, and the flange insulating materials are supplied as a kit, designed to provide insulation for one flange of a given size and type, for site installation.
12.2.3.2.2 The installation shall take place in clean and dry conditions.
12.2.3.2.3 Flanges on which insulating gaskets are to be installed shall be supplied as matched pairs or reamed on site to ensure correct alignment of bolt holes. The flange faces shall be clean and correctly aligned. Misaligned flanges will result in insulating sleeve damage during assembly or subsequent springing of the pipe. Flange faces shall be square and free of burrs to allow for correct sealing of nuts, bolts, and washers.
12.2.3.2.4 The flange shall be assembled using a very high impedance voltmeter attached across the "open" joint. During assembly, potential difference across the joint must not be lost. It may be necessary to create a potential difference across the "open" joint before commencing assembly.
Note:
Using resistance methods to determine integrity of insulating flanges in the field can produce irrelevant results.
12.2.3.2.5 Insulated flanges shall be assembled and tested before being welded into the pipeline. A voltage of 1500 volt DC shall be applied across the flange assembly for one minute without causing breakdown of the insulation or flash over. Subsequently the resistance across the assembled flange shall be measured and shall be more than 1 mega ohm (106 ohm).
12.2.3.2.6 On existing flanges, the bolt-to-pipe resistance shall be measured and the overall effectiveness of the isolated flange determined after cathodic protection has been applied. This can effectively be done by measuring the current through the attached pipe using a "Swain-type" current clamp/meter.
12.2.3.2.7 Insulated flanges shall be protected against ingress of dirt and moisture by the application of flange protectors or protective tape, except when used in sour service conditions.
12.2.3.2.8 The isolating gasket shall be carefully aligned between the flange faces and the bolt holes. It may be easier to use one size smaller diameter, high tensile steel bolts, and/or special thin-walled sleeving to assist alignment.
12.2.3.2.9 Alignment pins shall be inserted to ensure that flange alignment is maintained during the installation of the isolating sleeves.
12.2.3.2.10 The isolating sleeves are then positioned in the correctly aligned holes. Isolating sleeves must be of the correct length. If they are too long, they may be damaged when the bolt nuts are finally tightened. If they are too short, they may fail to isolate properly. The length of the isolating sleeve shall normally include the two isolating washers, except where alignment allows only one flange to be isolated.
12.2.3.2.11 The bolts, complete with isolating washers and steel washers under the bolt and nut heads, are threaded through the sleeves and hand tightened.
12.2.3.2.12 Final tightening to the tension recommended for the diameter and pressure rating of the flange shall be done in a sequence that provides for equal tensioning without distortion.
12.2.3.2.13 The original alignment pins may then the removed and bolts installed, complete with sleeves and washers as described above.
12.2.3.2.14 Complete flanges shall be coated in accordance with design specification.
12.2.3.2.15 To prevent the failure of the insulating materials and to obtain a satisfactory insulating job with a minimum of effort, the following precautions should be observed in installing insulating flanges:
Dec. 1997 IPS-C-TP-820
66
1) Micarta washers should be placed next to the flange and topped by steel washers which rest beneath the nut.
2) All micarta washers should be placed on the same half of the flange.
3) A back-up wrench should be placed on the nut nearest the micarta washer and all tightening of the flange bolt accomplished by turning the nut on the opposite half of the flange.
4) The micarta sleeve is designed to extend through both washers. Precautions should be taken to see that it remains in this position during installation work.
5) Micarta sleeves should never be hammered or forced into place.
TYPICAL TEST STATION INSTALLATIONS. (A) ISOLATING FLANGE IS OVERWRAPPED TO PREVENT INGRESS OF MOISTURE. THIS BASIC INSTALLATION ALLOWS POTENTIAL MEASUREMENTS TO BE TAKEN ON EITHER SIDE OF DEVICE. (B) INNER CABLES ARE LARGE CROSS SECTION AND ALLOW FOR RESISTANCE TO BE BONDED ACROSS JOINT AS REQUIRED. OUTER CABLES ARE FOR POTENTIAL MONITORING. TO ALLOW EASY IDENTIFICATION, CABLES SHALL BE PERMANENTLY IDENTIFIED
Fig. 6
12.2.3.3 Protection against external moisture ingress
12.2.3.3.1 The materials used for the isolating sleeves and washers may absorb water, and the construction of the joint may allow for moisture ingress, both of which will result in a reduction of the electrical resistance of the assembly. It is therefore essential to provide a protective coating. A suitable material may be applied to fill in the crevices and gaps between flange faces, and to mold around the flange faces so that a smooth profile is achieved which, together with the adjacent pipework, may be coated or wrapped to the same standard as the pipeline. Other methods and
Dec. 1997 IPS-C-TP-820
67
materials may be used to protect against moisture ingress.
12.2.4 Pipeline casing insulators
12.2.4.1 Pipeline casing insulators shall be installed in accordance with the manufacturer’s instructions. Special care shall be taken to ensure that all subcomponents are correctly assembled and tightened and that no damage occurs during carrier pipe insertion and tightening.
12.2.4.2 The annulus between the carrier pipe and the casing shall be sealed at each end of the casing by means of casing end seals to prevent water from entering the casing.
12.2.4.3 There must be no inadvertent metallic contact between the casing and the carrier pipe. The spacing of insulators shall ensure that the carrier pipe is adequately supported throughout its length, particularly at the ends, to prevent settling and possible shorting.
12.3 High Voltage Protection
12.3.1 Isolating devices and supports shall be protected against damage from high voltage surges. These surges may be caused by lightning, induced AC from adjacent or overhead high tension cables, or fault conditions.
12.3.2 High voltage surges may permanently damage the isolating materials used in the joint construction.
12.3.3 Isolating devices and supports may be protected with lightning arrestors, electrolytic grounding cells, polarization cells, or combinations of these.
12.3.4 The manufacturer’s instructions should be followed strictly when installing protective devices. In particular, they shall be physically secured and the connection cables properly sized.
12.3.5 The threshold rating of the protective device shall be such that, even allowing for tolerances, the potential applied across the isolating device is below its minimum dielectric strength.
12.3.6 Lightning arrestors and other protective devices may need to be carefully located or housed to prevent dirt and moisture from collecting, which could lead to an external flashover at a relatively low surge voltage. Applicable electrical codes shall be consulted.
13. THERMIT WELDING OF CATHODIC PROTECTION LEADS
13.1 Introduction
This Clause 13 covers the connection of cathodic protection wire leads to new or in-service carbon steel pipelines under pressure by thermit welding. Connections to pipe less than 3 mm thick shall be made using approved clamps or silver soldering.
13.2 General
13.2.1 For the purposes of this Standard, thermit welds, thermowelds and cadwelds are synonymous.
13.2.2 Thermit weld process shall be applied only by skilled experienced field personnel.
13.2.3 Thermit welds shall not be made on internally plastic coated pipelines. Internal coatings affected include epoxies, phenolics, nylon, polyethylene liners, etc.
13.2.4 The thermit weld charge shall be limited to Thermoweld Cartridge No. 15 F33 (15 gram), or equivalent. 13.2.5 The maximum size of the electrical conductor shall be 25 Sq.mm (No. 6 AWG). Where the attachment of a larger conductor is required, a multistrand wire shall be used and the strands shall be arranged into groups no larger than 25 Sq.mm (No. 6 AWG) and each group attached to the pipe separately.
13.2.6 The minimum distance of a thermit weld from a circumferential weld shall be 200 mm.
Dec. 1997 IPS-C-TP-820
68
13.2.7 The minimum distance of a thermit weld from a longitudinal weld shall be 40 mm.
13.2.8 In attaching one wire to a pipeline only one charge shall be used. If the first thermit weld does not take, a second thermit weld shall not be attempted on the same spot.
If a thermit weld is disapproved on the first charge, it shall either be removed, the surface cleaned to bright metal and the process is repeated or a new location on the pipe is selected.
13.2.9 The permissible operating pressure in the pipeline when thermit welding is shown in Table 1. If the pipe on which the thermit weld will be attached is not in the table, the permissible operating pressure can be calculated using the following formula: D10³ 0.72 1.59) -(t 2S××=PP
PP = Permissible "hot work" pressure (Kpa).
S = Specified minimum yield strength of the pipe (MPa).
D = Nominal outside diameter of the pipe (mm).
t = Nominal wall thickness of the pipe (mm).
Note:
S, D, and t values are to be obtained from the operating permits for the pipeline.
13.2.10 Thermit welds shall not be attached to pipe wall thicknesses less than 3.18 mm while the pipeline is pressurized.
13.2.11 The connection of leads to high pressure gas lines with wall thickness less than 4.78 mm, but more than 3.18 mm by thermit welding shall be done with the gas flowing.
13.2.12 The use of thermit welds shall be avoided in high stress areas such as elbows, tees, etc.
13.2.13 If more than one weld is required such as two adjacent wires or large conductor split in two to get the required size for a 15 gram charge, the spacing between point of connection shall not be less than 100 mm (4 inches).
A suitable copper sleeve for smaller size wire shall be used for a 15 gram one shot mold and the wire bended around the end of the sleeve.
13.3 Pipe Preparation
13.3.1 The pipeline coating shall be completely removed including primer and the pipe cleaned with a file to white metal. The pipe shall be completely dry.
13.3.2 The wall thickness of the pipe shall be checked using a portable ultrasonic wall thickness tester and the permissible pressure of the line checked.
13.3.3 Where possible thermit welds shall be applied to horizontal pipes.
13.4 Thermit Weld Preparation and Procedure
13.4.1 Care shall be taken to ensure that the graphite thermit weld mold is completely dry and free from slag or other impurities before proceeding with thermit welding on pressurized pipelines.
13.4.2 The copper conductor shall be clean and dry and the insulation cut back sufficiently for insertion into the mold.
13.4.3 The copper conductor shall be wrapped around the pipe at least once and enough slack provided to allow for pipe in soil movement.
13.4.4 The thermit welding shall be done in accordance with the steps indicated in the IPS drawing No. IPS-D-TP-702.
13.4.5 After the completion of the thermit weld on buried pipelines, the bright metal surfaces shall be protected and covered by the application of a P.E. tape & primer and a "Royston Handy Cap" or
Dec. 1997 IPS-C-TP-820
69
equal. The "Handy Cap" shall be taped in place using primer and cold applied self adhesive P.E. tape to provide a watertight seal on all exposed steel and copper surfaces.
The tape shall overlap existing pipe coating to about 25 mm (1 inch) minimum.
Manufacturer’s instruction for application of "Handy Cap" shall be rigidly followed.
TABLE 1 - PERMISSIBLE HOT WORK PRESSURE WHILE THERMIT WELDING
NPA
GRADE
SPECIFIED
MINIMUM
YIELD
O.D.
W.T.
PERMISSIBLE
HOT WORK
PRESSURE
CSA
API
MPa
PSI
mm
inch
mm
inch
kPa
psig
2
207
241
A
B
207
241
30000
35000
60.3
60.3
2.375
2.375
3.91
3.18
0.154
0.125
11 529
9 170
1 664
1 330
3
241
290
A
X42
241
290
35000
42000
88.9
88.9
3.500
3.500
3.18
4.78
0.125
0.188
6 205
15 059
900
2 169
4
241
290
B
X42
241
290
35000
42000
114.3
114.3
4.500
4.500
3.18
4.78
0.125
0.188
4 826
11 713
700
1 687
6
207
241
290
A
B
X42
207
241
290
30000
35000
42000
168.3
168.3
168.3
6.625
6.625
6.625
4.78
4.78
3.18
0.188
0.188
0.125
5 678
6 610
3 930
818
955
570
8
207
241
290
A
B
X42
207
241
290
30000
35000
42000
219.1
219.1
219.1
8.625
8.625
8.625
5.56
8.18
4.17
0.219
0.322
0.164
5 427
10 486
4 977
783
1 516
722
10
241
317
317
B
X46
X46
241
317
317
35000
46000
46000
273.1
273.1
273.1
10.750
10.750
10.750
6.35
5.56
4.78
0.250
0.219
0.188
6 077
6 668
5 308
879
964
770
12
290
317
359
X42
X46
X52
290
317
359
42000
46000
52000
323.9
323.9
323.9
12.750
12.750
12.750
6.35
6.35
4.78
0.250
0.250
0.188
6 166
6 740
5 060
889
974
734
14
290
317
X42
X46
290
317
42000
46000
355.6
355.6
14.000
14.000
6.35
5.59
0.250
0.219
5 616
5 122
810
743
16
317
359
X46
X52
317
359
46000
52000
406.4
406.4
16.00
16.00
6.35
5.59
0.250
0.219
5 372
5 067
776
735
Note:
The wall thickness of the pipe to be worked on is to be checked with an Ultrasonic Wall Thickness Tester after the pipe has been cleaned for welding. The thermit weld is not to be made on a pitted or laminated pipe or where the wall thickness is less than 90% of nominal pipe wall thickness.
Dec. 1997 IPS-C-TP-820
.




آمار وبلاگ
  • کل بازدید :
  • بازدید امروز :
  • بازدید دیروز :
  • بازدید این ماه :
  • بازدید ماه قبل :
  • تعداد نویسندگان :
  • تعداد کل پست ها :
  • آخرین بازدید :
  • آخرین بروز رسانی :
پی کو باکس کسب درآمد
امکانات جانبی
به سایت ما خوش آمدید
     
کلیه حقوق این وبلاگ برای انسانم آرزوست... محفوظ است