GB/T 15181-1994 Volumetric calibration method for spherical metal tanks (circumferential tape method)

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1. Method number / full name / English name / replacement relationship

• Standard number: GB/T 15181-94
• Chinese full name: Volumetric calibration method for spherical metal tanks (circumferential tape method)
• English name: Capacity calibration of spherical metal tanks—Strapping method
• Replacement relationship: not provided in the available source
• Publication/implementation: issued by 1994-08-23, implemented by 1995-06-01 (State Bureau of Technical Supervision)
• UDC: 621.642; E 98

2. Scope of application and non-applicability

• Scope of application: This standard specifies the measurement method and calculation steps for calibrating the volume of spherical metal tanks by the circumferential tape method; it is applicable to newly built or overhauled spherical metal tanks that have not contained liquid (Chapter 1).
• Not applicable: It is not applicable to spherical metal tanks with a double-layer structure (Chapter 1).

3. Method principle

No centralized statement of the principle chapter is provided in the available source. From Chapters 7 and 8, it can be summarized as follows: by directly measuring the equatorial circumference or vertical circumference with a steel circumferential tape (or indirectly deriving the equatorial radius by measuring a circumference deviating from the equator or by the optical plumb-line method), and combining parameters such as plate thickness, total internal height of the tank, span correction, temperature, and oil gauge tape correction, the equatorial internal diameter, vertical internal diameter, and total internal height of the tank are calculated, and then the total volume of the empty tank (20℃), pressure-bearing volume, etc. are calculated (Chapters 7 and 8).

4. Reagents and materials (purity / preparation)

Not provided in the available source (this standard is a geometric measurement method and does not list reagents).

5. Instruments and equipment

• 6.1 Steel circumferential tape: shall meet the requirements of GB 13236.
• 6.2 Oil gauge tape: shall meet the requirements of GB 13236.
• 6.3 Dynamometer: 0~100 N, with a minimum division value not greater than 2 N.
• 6.4 Magnetic base: vertical suction force not less than 588 N.
• 6.5 Optical plumb instrument: optical verticality not lower than 1/20 000.
• 6.6 Level: accuracy not lower than S₃ grade (the source text says “Ss grade”, requires confirmation against the source standard (source-text extraction)).
• 6.7 Ultrasonic thickness gauge: minimum division value 0.1 mm.
• 6.8 Theodolite: accuracy not lower than DJ grade (the source text says “DJ grade”, requires confirmation against the source standard (source-text extraction)).
• 6.9 Span gauge: shaped like a gate, with needle-point ends.
• 6.10 Projection plate: steel, dimensions not less than 250 mm×250 mm×5 mm.
• 6.11 Thermometer: −30~50 ℃, with a minimum division value not greater than 0.5 ℃.
• 6.12 Tape adjusting rod.
• 6.13 Tape clamp.

6. Recommended operating conditions

• Calibration must be carried out after the pressure test is qualified and before the tank body is insulated (4.2).
• The ground under the tank must be level and free of obstacles that affect measurement (4.3).
• The acceptance of spherical tanks shall meet the requirements of GB 12337 (4.1).
• All measurement data shall be read and recorded to one decimal place (Chapter 7).
• Circumferential tape tension: for equatorial circumference measurement, apply 50 N tension (7.1.1.2); for equatorial radius measurement, apply 50 N tension at about 1 m behind the measuring station (7.1.3.4); for vertical circumference, apply 50 N tension at each end of the tape (7.2.1).
• Safety measures: climbing facilities such as scaffolding or movable ladders must be firm and reliable (5.1); calibration personnel must wear appropriate protective equipment (5.2); electrical equipment used must meet the corresponding explosion-proof rating requirements (5.3).

7. Sampling and sample preparation

Not provided in the available source (this is on-site calibration, with no sampling or preparation content).

8. Analysis procedure

• 7.1 Measurement of equatorial circumference or radius
  • 7.1.1 Direct measurement of equatorial circumference
    • 7.1.1.1 According to different tank body structural types (Figure 1: three-band plate, four-band plate, five-band plate tank bodies), mark the circumferential tape path with a colored pen at 1/2 of the vertical arc length between the equatorial plate or the welds of the upper and lower polar plates.
    • 7.1.1.2 Wrap the steel circumferential tape once around the tank wall along the circumferential tape path, check and adjust the tape so that it fits closely against the lower edge of the path, tighten the tape, fix one end with a magnetic base, apply 50 N tension at the other end, and read the value corresponding to the zero point of the steel circumferential tape.
    • 7.1.1.3 Carry out a second measurement at about 500 mm away from the original starting point of the circumferential tape. The difference between two consecutive circumferential tape measurement values shall not exceed one ten-thousandth of their arithmetic mean; if within the allowable tolerance, take the arithmetic mean as the equatorial circumference C' (mm); otherwise, re-measure.
  • 7.1.2 Indirect measurement of equatorial circumference (when the tank support columns are higher than the equator)
    • 7.1.2.1 Determine the equatorial position according to Clause 7.1.1.1.
    • 7.1.2.2 Determine the position deviating from the equatorial circumference at 100~300 mm above the top of the support column, and at the same time measure the deviation distance h (mm); h may also be replaced by the vertical arc length (Figure 2).
    • 7.1.2.3 At the determined measurement position, measure the deviating equatorial circumference Cₘ according to Clauses 7.1.1.2 and 7.1.1.3 (mm).
  • 7.1.3 Measurement of equatorial radius (when the equator and deviating equatorial positions do not permit circumferential tape measurement, the optical plumb-line method is used)
    • 7.1.3.1 Instrument inspection: level the optical plumb instrument, align the line of sight of the upper plumb with a horizontal straight ruler at the equatorial position, align the line of sight of the lower plumb with a horizontal straight ruler on the ground, and read the values on both rulers; rotate 180° and read again. If the difference between two readings on the same horizontal ruler is not greater than 1 mm, the vertical performance is good; otherwise, identify the cause and re-inspect.
    • 7.1.3.2 Projection of the tank body center: a. Level the optical plumb instrument at the lower center of the tank body, align the line of sight of the upper plumb with the lowest point of the tank body (the center of the manhole or drain pipe), project the line of sight of the lower plumb to the ground, roughly determine the ground projection position of the tank body center point O, and place the projection plate with white paper attached at this position; b. Set three measurement points A, B, and C on the ground around the tank at intervals of about 120°, and at each point use a theodolite to be tangent to the left and right points of any horizontal section of the tank body (the sections formed by the three measurement points may not coincide), and draw three projection lines AA', BB', and CC' on the projection plate in the a/2 direction, intersecting to form a triangle; take the intersection of the angle bisectors of the triangle as the ground projection point O' of the tank body center (Figure 3).
    • 7.1.3.3 Evenly arrange eight plumb measurement stations along the ground projection of the tank equator (Figure 4).
    • 7.1.3.4 Level the optical plumb instrument at each plumb measurement station, with the line of sight of the upper plumb clearly tangent to the equatorial line; align the zero line of the steel circumferential tape with the tank body center projection point O', fix and press it tightly, lead the other end horizontally toward the measurement station, apply 50 N tension at about 1 m behind the measurement station, read the steel circumferential tape value on the line of sight of the lower plumb of the optical plumb instrument, and successively measure the horizontal distances from O'—B₁, O'—B₂……O'—B₈ points (Figure 5), and take the arithmetic mean as R'₀.
    • 7.1.3.5 While measuring the equatorial radius, measure the atmospheric temperature t₁ and the internal tank temperature t₂.
• 7.2 Measurement of vertical circumference
  • 7.2.1 Lower the tape from the top of the tank so that the tape passes through the upper and lower poles and goes around the tank wall once, adjust the tape with the tape adjusting rod to make it vertical, apply 50 N tension at each end of the tape, and read the value corresponding to the zero mark; carry out a second measurement away from the original starting point; the difference between the two measurement values shall not exceed one ten-thousandth of their arithmetic mean; take the arithmetic mean as the first vertical circumference C₂.
  • 7.2.2 At the pole intersecting the first vertical circumference at 90°, measure the second vertical circumference C₃ according to Clause 7.2.1.
  • 7.2.3 When the pole encounters an obstacle, avoid the obstacle and carry out deviating pole measurement according to Clauses 7.2.1 and 7.2.2; the selected upper and lower measurement points must be in opposite directions and at equal distances from the upper and lower poles.
  • 7.2.4 When direct circumferential tape measurement is difficult, the segmented arc length measurement method may be used, that is, measure the arc length of the obstacle segment and the arc lengths of two segments symmetrically on the left and right of the tank body outside the obstacle segment, thereby obtaining C₂ or C₃ (the arc length of the obstacle segment is measured using a large “「”-shaped span gauge, taking the chord length of the obstacle segment, and comparing it on the smooth tank body arc surface).
• 7.3 Measurement of span correction: while measuring the circumference, use the span gauge to measure the span correction for welds or obstacles passed over by the steel circumferential tape. With the obstacle as the center, use the span gauge to measure the arc length with the obstacle; then select a tape segment where the steel circumferential tape fits closely against the tank wall, and use the span gauge with fixed length to measure the arc length without the obstacle; the difference between the arc length without the obstacle and the arc length with the obstacle is the “span correction”.
• 7.4 Measurement of total internal height of the tank
  • 7.4.1 Drop the oil gauge tape from the upper pole to the lower polar plate, measure the total internal height of the tank, and read accurately to 1 mm.
  • 7.4.2 When the upper pole encounters an obstacle and cannot be measured directly, move away from the pole to an unaffected point M, measure the vertical height Hₘ at point M (mm) (Figure 6), and use a steel tape to measure the horizontal distance L from point M to the tank internal center line (or the upper and lower poles) (mm), reading accurately to 1 mm.
• 7.5 Plate thickness measurement: use a thickness gauge and steel tape to measure along the tank wall the plate thickness Sᵢ (mm) and vertical arc length hᵢ (mm) in each region, read thickness to 0.1 mm, estimate arc length to 0.5 mm, and calculate the weighted average plate thickness S according to formula (1) (mm).
• 7.6 Measurement of the correction value for the height from the zero position of the liquid level gauge scale to the zero point of the tank bottom: see Appendix A.
• 7.7 Record: record the working pressure P of the calibrated spherical tank during use (MPa).

9. Qualitative and quantitative determination and calculation formulas

• 8.1 Calculation of net circumference
  • 8.1.1 Direct measurement of the net circumference Cₙ (mm): formula (2), where C'ₙ is the directly measured circumference (mm, n=1,2,3); ΔL is the correction value of the steel tape (mm); ΔL₂ is the sum of the crossing corrections of the steel tape (mm). The calculation result shall be retained to one decimal place.
  • 8.1.2 Indirect measurement of the net equatorial circumference C₁ (mm): C₁=√(Cₘ²+(2h)²), where Cₘ=C'ₘ+ΔL+ΔL₂; where Cₘ is the corrected circumference deviating from the equator (mm); C'ₘ is the circumference measured deviating from the equator (mm); h is the vertical distance from the circumference deviating from the equator to the equator (mm). The calculation result shall be retained to one decimal place.
• 8.2 Calculation of inner diameter
  • 8.2.1 Equatorial inner diameter D₁ (mm): formula (3), D₁=C₁/π−2S₁ (the original formula is typeset as "D, -A-2S,", requires confirmation against the source standard (source-text extraction)), where S₁ is the thickness of the equatorial plate (mm). The calculation result shall be retained to one decimal place.
  • 8.2.2 Equatorial inner diameter when measuring the equatorial radius by the optical plumb line method D₁ (mm): D₁=2{R'₀[1+α(t₁−t₂)]+ΔL−2S₁} (the original formula (4) is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)); where R'₀ is the arithmetic mean of the measured equatorial radii (mm); t₁ is the temperature of the steel tape (taken as the atmospheric temperature at the tank bottom, ℃); t₂ is the tank body temperature (taken as the arithmetic mean of the atmospheric temperature and the temperature of the space inside the tank, ℃); α is the linear expansion coefficient of the steel tape (generally for steel tape take 11.5×10⁻⁶, for stainless steel tape take 14×10⁻⁶, ℃⁻¹). The calculation result shall be retained to one decimal place.
  • 8.2.3 Vertical inner diameter D₂, D₃ (mm): formulas (5), (6), (7) (the original formulas are incomplete in typesetting, requires confirmation against the source standard (source-text extraction)), where S is the weighted average plate thickness of the tank body (mm). The calculation result shall be retained to one decimal place.
• 8.3 Calculation of total inner height of the tank H
  • 8.3.1 Measured from the pole point: formula (8) (the original formula is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)), where H' is the vertical inner height of the tank measured from the upper pole point of the spherical tank (mm); t₃ is the temperature of the oil gauging tape (taken as the temperature of the space inside the tank, ℃); ΔL₃ is the correction value of the oil gauging tape (mm). The calculation result shall be taken as an integer mm.
  • 8.3.2 Measured from point M: H=√{(Hₘ+ΔL₃)²+L²·[1+α(t₃−t₂)]} (the original formula (9) is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)); where Hₘ is the vertical inner height of the tank measured at point M (mm); L is the horizontal distance from point M to the vertical center line inside the tank (or the center point of the upper and lower pole plates) (mm). The calculation result shall be taken as an integer mm.
• 8.4 Calculation of the total volume of the empty tank (20℃) V (dm³): the original formula is not provided in the available source (formula (10) is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)). The calculation result shall be accurate to dm³.
• 8.5 Calculation of pressure-bearing volume
  • 8.5.1 Increase value of total pressure-bearing volume ΔV (dm³): formula (11) (the original formula is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)), where D is the arithmetic mean of D₁, D₂, D₃ (mm); P is the working pressure of the spherical tank being calibrated (MPa); E is the Young's modulus of elasticity of carbon steel (206×10³, MPa) (the original "206×10" requires confirmation against the source standard (source-text extraction)). The calculation result shall be accurate to dm³.
  • 8.5.2 Total pressure-bearing volume V₁ (dm³): V₁=V+ΔV. The calculation result shall be accurate to dm³.
  • 8.5.3 Partial pressure-bearing volume V₂ (dm³): formula (13) (the original formula is incomplete in typesetting, requires confirmation against the source standard (source-text extraction)), where H is the total inner height of the tank (cm); l is the height for calculating the partial volume (cm). The calculation result shall be accurate to dm³.
• Appendix A Correction value for the height from the zero position of the liquid level gauge scale to the zero point of the tank bottom: ΔH=H₁−(H₂+S_L) (formula A1); where H₁ is the height from the zero position of the liquid level gauge scale to the horizontal line of sight (mm); H₂ is the height from the center point O of the outer bottom of the tank to the horizontal line of sight (mm); S_L is the thickness of the lower pole plate (mm). The liquid level height inside the tank is equal to the observed liquid level value plus the height correction value.
• Appendix C Temperature correction: V_t=V₂₀+π·h·R²·α(t−20)×10⁻⁶ (the original typesetting is "V. =V2o + xh"R•a (t-20)X 10-6", requires confirmation against the source standard (source-text extraction)); where t is the tank wall temperature (for insulated tanks take the liquid temperature inside the tank, for non-insulated tanks take the average of the liquid temperature inside the tank and the atmospheric temperature around the tank body, ℃); V₂₀ is the corresponding volume found in the volume table according to the liquid level height inside the tank (dm³); R is the average inner radius of the tank body (mm); h is the liquid level height inside the tank after temperature correction (mm); α is the linear expansion coefficient of carbon steel (take 11.5×10⁻⁶, ℃⁻¹) (the original "11-5 10-®" requires confirmation against the source standard (source-text extraction)).

10. Precision

• The difference between two consecutive tape measurements shall not exceed one ten-thousandth of their arithmetic mean (7.1.1.3, 7.2.1).
• Optical plumb line inspection: the difference between two readings on the same horizontal straightedge shall not exceed 1 mm (7.1.3.1).
• Total uncertainty: the total uncertainty of the volume calibration results of this standard is less than 0.2% (95% confidence level) (Chapter 10).

11. Report

• Issue a calibration report with reference to Appendix C (Chapter 9).
• Appendix C Calibration report format (reference item) contents include: calibration report number (Rong Biao Zi No. ), spherical tank number, structural type, design capacity, applicant unit, manufacturing unit, installation unit, calibration method, calibration unit, calibration conclusion, calibration date, person in charge, verifier, calibrator, calibration results (total volume dm³, average inner radius of tank body mm, volume table total pages, liquid level height correction value ΔH mm).
• Note: 1. This volume table is the volume at 20℃, and when used for precision measurement it shall be corrected according to the temperature correction formula; 2. If the volume of accessories needs to be considered, it may be carried out according to the provisions of GB 13235.1; 3. This volume table already includes the volume increase value under the working pressure inside the tank (MPa); 4. After major repair or severe deformation of the tank body, re-calibration shall be applied for.
• Volume table format: tank number, Rong Biao Zi No. , page ; height (cm), volume (dm³); printed by, proofread by.

12. Reference documents

• GB 12337 Steel spherical storage tanks
• GB/T 13235.1 Petroleum and liquid petroleum products—Calibration of vertical cylindrical metal tanks—Tape method
• GB 13236 Technical conditions for petroleum gauging tapes and steel tapes
• Reference adoption: American Petroleum Institute and American Society for Testing and Materials joint standard API 2152-36 (87)—ASTM D1408—65 (90) "Methods for Measurement and Calibration of Spherical and Spheroidal Tanks" (the original "AP12152-36 (87)--AS1M-D1408—65 (90)", requires confirmation against the source standard (source-text extraction))

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference for Questions and Answers