17 4/pgs Manual of Petroleum Measurement Standards Chapter 17—Marine Measurement Section 4—Method for Quantification of Small Volumes on Marine Vessels (OBQ/ROB) FIRST EDITION, OCTOBER 1994 Manual of[.]
Introduction
The purpose of this standard is to provide a method for de- termining the small volumes of on-board quantity (OBQ) prior to loading a vessel or material remaining on board
(ROB) a vessel upon completion of discharge.
Scope and Field of Application
This standard is specifically focused on the manual gauging of small volumes on marine vessels, applicable before loading or after discharge It excludes considerations for clingage, hydrocarbon vapors, cargoes in transit, and cargo pumpability, as detailed in API MPMS Chapter 3.
Definitions
For the purposes of this standard, the following definitions apply.
17.4.3.1 clingage: cargo that adheres to all surfaces of the emptied portion of the tank other than bottom surfaces.
17.4.3.2 liquid volume: the measurable amount of ma- terial that is free flowing at the time of measurement.
17.4.3.3 multipoint gauging: the activity of measur- ing cargo in a vessel tank through two or more openings in the top of the tank.
Nonliquid volume refers to the quantifiable amount of material that is not in a free-flowing state during measurement This category of nonliquid material can consist of various substances, including hydrocarbon waxes, water/oil emulsions, sediment, or solidified cargo.
On-board quantity (OBQ) refers to the materials present in a vessel's cargo tanks, void spaces, and pipelines prior to loading This quantity can consist of various substances, including water, oil, slops, oil residue, oil/water emulsions, and sediment.
17.4.3.6 remaining on board (ROB): the material re- maining in a vesselÕs cargo tanks, void spaces, and pipelines after the cargo is discharged Remaining on board quantity
SECTION 4—METHOD FOR QUANTIFICATION OF SMALL VOLUMES ON
1 American Conference of Governmental Industrial Hygienists, 6500 Glen- way Avenue, Building D-7, Cincinnati, Ohio 45211.
2 International Chamber of Shipping, 30/32 Mary Axe Street, London EC3A 8ET, England.
3 Oil Companies International Marine Forum, Portland House, 6th Floor, Stag Place, London SW1E 5BH, England.
4 International Association of Ports and Harbors, Kotohira-Kaikan Building, 2-8, Toranomon 1-Chome Minato-Ku, Tokyo 105, Japan.
5 ISGOTT is available from Witherby & Co., Ltd (Marine Publishing), 32/36 Aylesbury Street, London EC1R 0ET, England.
6 Occupational Safety and Health Administration, U.S Department of Labor.The Code of Federal Regulations is available from the U.S GovernmentPrinting Office, Washington, D.C 20402.
Before taking any OBQ/ROB measurements, record the trim and list of the vessel The vessel should be requested to eliminate or minimize any list.
All areas on the vessel that may hold On Board Quantity (OBQ) or Remaining On Board (ROB) must be measured and recorded before loading and after discharge This gauging process should follow the guidelines specified in API MPMS Chapter 3 and Chapter 17, Sections 1 and 2.
Gauging the Onboard Quantity (OBQ) and Remaining Onboard Quantity (ROB) at various points within a vessel compartment is essential for determining the even distribution of material across the tank bottom When multiple gauging points are accessible, it is important to manually take and record measurements from each point.
Temperatures must be measured and documented for cargo volume adjustments when the material's depth and nature allow If temperature measurement is not feasible, the gross observed volume should be reported as gross standard volume (GSV).
Temperature measurements shall be obtained in accor- dance with API MPMS Chapter 17, Section 2, and Chapter
Note: Volume correction factors are not applicable to nonliquid volumes (see API MPMS Chapter 3, Section 1A).
When OBQ/ROB is available, it is essential to collect samples from all compartments with liquid volume, as well as from nonliquid volumes when possible The samples must be of adequate quantity to facilitate necessary analyses and should be collected following the guidelines outlined in API MPMS Chapter 8, Section 1.
17.4.5.4 VESSEL CARGO LINES AND PUMPS
The vessel must ensure that all cargo lines and pumps are thoroughly drained and stripped before the final OBQ/ROB measurement Ideally, the smallest tank on the vessel should be selected to collect the drained material from these lines and pumps It is essential to gauge this designated tank both prior to and following the draining process.
Slops must be accurately measured and reported on the OBQ/ROB form during loading and discharge at ports, following the procedures for slop tanks specified in API MPMS Chapter 17, Section 2 This includes a mixture of water, oil, slops, oil residue, oil/water emulsion, and sediment.
17.4.3.7 sediment: solid materials including, but not limited to, sand, rust, and scale.
Sludge refers to the non-free flowing material found in a ship's cargo tank, primarily composed of hydrocarbon waxes It may also include water/oil emulsions and sediment The use of the term "sludge" is generally discouraged.
The wedge formula (17.4.3.9) is a mathematical tool used to estimate small quantities of measurable liquid and non-liquid materials on board a vessel, particularly when they are in a wedge configuration and do not contact all bulkheads of the tank This formula takes into account the characteristics of the cargo compartment, the trim of the vessel, and the depth of the material.
The wedge table, identified as 17.4.3.10, is a calculated volume table for a vessel's cargo tank that utilizes the wedge formula This table is particularly useful when the cargo does not make contact with all the tank's bulkheads, simplifying the process during cargo transfers by eliminating the need for manual calculations using the wedge formula.
17.4.3.11 Other terms used in this standard are defined in
API MPMS Chapter 1 or other API petroleum-measurement standards.
Safety and Health Considerations
When addressing safety procedures, it is essential to consider various factors, including electrostatic hazards, personnel exposure, and the risks of explosive and toxic environments within cargo tanks Evaluating the physical properties of the cargo and current operational conditions is crucial, along with adhering to relevant international, federal, state, and local regulations.
Safety procedures designated by the employer, the vessel op- erator, and other concerned parties should also be observed.
Internationally, the International Safety Guide for Oil
Tankers and Terminals (ISGOTT)and appropriate Oil Com- panies International Marine Forum (OCIMF) and API pub- lications provide additional safety information and should be consulted See Appendix A.
Quantification Procedures
Gauging
Before taking any OBQ/ROB measurements, record the trim and list of the vessel The vessel should be requested to eliminate or minimize any list.
All areas on the vessel that may hold On Board Quantity (OBQ) or Remaining On Board (ROB) must be measured and recorded before loading and after discharge This gauging process should follow the procedures specified in API MPMS Chapter 3 and Chapter 17, Sections 1 and 2.
Gauging the Onboard Quantity (OBQ) and Remaining Onboard Quantity (ROB) at various points within a vessel compartment is essential for determining the even distribution of material across the tank bottom When multiple gauging points are accessible, it is important to manually take and record measurements from each point.
Temperatures
Temperatures must be measured and documented for cargo volume adjustments when the material's depth and nature allow If temperature measurement is not feasible, the gross observed volume should be reported as gross standard volume (GSV).
Temperature measurements shall be obtained in accor- dance with API MPMS Chapter 17, Section 2, and Chapter
Note: Volume correction factors are not applicable to nonliquid volumes(see API MPMS Chapter 3, Section 1A).
Sampling
When OBQ/ROB is available, it is essential to collect samples from all compartments with liquid volume, as well as from nonliquid volumes when possible The samples must be of adequate quantity to facilitate necessary analyses and should be collected following the guidelines outlined in API MPMS Chapter 8, Section 1.
Vessel Cargo Lines and Pumps
The vessel must ensure that all cargo lines and pumps are thoroughly drained and stripped before the final On Board Quantity (OBQ) and Remaining On Board (ROB) measurements are taken Ideally, the smallest tank on the vessel should be selected to collect the drained material from these lines and pumps It is essential to gauge this designated tank both prior to and following the draining process.
Slops
Slops should be accurately measured, quantified, and documented on the OBQ/ROB form during loading and discharge at ports, following the slop tank procedures specified in API MPMS Chapter 17, Section 2 This may consist of various mixtures, including water, oil, slops, oil residue, oil/water emulsion, and sediment.
17.4.3.7 sediment: solid materials including, but not limited to, sand, rust, and scale.
17.4.3.8 sludge: that element of the material in a shipÕs cargo tank that is essentially not free flowing Sludge con- sists of hydrocarbon waxes and may contain water/oil emul- sions and sediment The use of this term is not recommended.
17.4.3.9 wedge formula: a mathematical means to ap- proximate small quantities of measurable liquid and/or nonliquid material on board that is in a wedge configuration and does not touch all bulkheads of the vesselÕs tank The formula is based on cargo compartment characteristics, ves- sel trim, and the depth of the material.
17.4.3.10 wedge table: a vesselÕs cargo tank volume table calculated on the wedge formula for use when cargo does not touch all bulkheads of the tanks Wedge tables pre- clude the need for calculation by wedge formula at times of cargo transfer.
17.4.3.11 Other terms used in this standard are defined in
API MPMS Chapter 1 or other API petroleum-measurement standards.
When addressing safety procedures, it is essential to consider various factors, including electrostatic hazards, personnel exposure, and the risks of explosive and toxic environments within cargo tanks Evaluating the physical properties of the cargo and current operational conditions is crucial, alongside adherence to relevant international, federal, state, and local regulations.
Safety procedures designated by the employer, the vessel op- erator, and other concerned parties should also be observed.
Internationally, the International Safety Guide for Oil
Tankers and Terminals (ISGOTT)and appropriate Oil Com- panies International Marine Forum (OCIMF) and API pub- lications provide additional safety information and should be consulted See Appendix A.
Appendix B includes examples of small volume calculations and configurations, while Appendix C presents a sample OBQ/ROB report form Additionally, Appendix D offers an explanation and example of the wedge formula, along with a wedge calculation worksheet.
OBQ/ROB Characteristics
Liquid Material
Liquid materials can consist of liquid petroleum, suspended sediments, and water, including free water The interface of free water can be detected using water-finding paste or electronic interface detectors To accurately assess the composition of these liquid materials, it is essential to collect and analyze samples.
When a vessel is not on an even keel, it is essential to quantify liquid volumes using trim/list correction, a wedge table, or the wedge formula If the liquid touches all bulkheads, a trim correction should be applied to the vessel's tank calibration tables, or a trim table must be utilized Conversely, if the liquid does not contact all bulkheads, the wedge table or wedge formula should be employed For further details, refer to Appendix D.
In a compartment where both liquid and nonliquid materials are present, the liquid volume can be determined by subtracting the nonliquid volume from the total observed volume of OBQ/ROB.
Nonliquid Material
17.4.6.2.1 To accurately determine the composition of nonliquid material, samples must be taken and examined or tested.
17.4.6.2.2 Nonliquid material may be in a wedge condi- tion Multipoint gauging is recommended to determine if a wedge condition exists.
Accurate calculations using the wedge formula require knowledge of the vessel's trim at the time the material solidified, as the formula incorporates a trim factor to determine the quantity.
For accurate volume determination of materials that are not in a wedge shape, it is essential to use the average of multiple readings In cases where only a single gauge point is accessible, it should be assumed that the material is evenly distributed across the tank bottom.
Calculating Quantities
After carefully assessing the configuration of the material in the tank, calculate the materialÕs volume according to the illustrative examples, formulae, and forms given in Ap- pendixes B through D.
S ECTION 4—M ETHOD FOR Q UANTIFICATION OF S MALL V OLUMES ON M ARINE V ESSELS (OBQ/ROB) 3
A.1 Physical Characteristics and Fire Considerations
Personnel handling petroleum and chemical substances must understand their physical and chemical properties, including fire, explosion, and reactivity risks, as well as emergency procedures Compliance with company safety practices and local, state, and federal regulations is essential, including the use of appropriate protective gear Additionally, personnel should remain vigilant to prevent ignition sources and ensure that containers are closed when not in use.
A.1.2 API Publications 2217 and 2026 and any applicable regulations should be consulted when sampling requires entry into confined spaces.
A.1.3 INFORMATION REGARDING PARTICULAR MATERIALS AND CONDI- TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER
OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.
Exposure to chemicals in the workplace can lead to potential health effects, which depend on the chemical's toxicity, concentration, and duration of exposure To minimize risks, individuals should take precautions such as reducing skin and eye contact, avoiding inhalation of vapors, and keeping chemicals away from the mouth to prevent harmful ingestion It is essential to keep containers closed when not in use, maintain clean and well-ventilated work areas, and promptly clean up spills following safety regulations Additionally, observing established exposure limits and using appropriate protective clothing and equipment is crucial for safety.
Information on exposure limits can be found by consulting the most recent editions of the
Occupational Safety and Health Standards, 29 Code of Federal Regulations, Sections
1910.1000 and following, and the ACGIH publication Threshold Limit Values for Chemical
Substances and Physical Agents in the Work Environment.
It is essential to obtain information regarding safety and health risks, as well as proper precautions related to specific materials and conditions, from the employer, the manufacturer, or the Material Safety Data Sheet (MSDS).
No trim correction or wedge formula applicable Volume to be obtained directly from vesselÕs calibration tables.
EXAMPLE(all units in meters)
When multiple soundings are taken, calculate the mathematical average and refer to the vessel's calibration tables In this case, with three soundings available, the average is used; however, if only one sounding can be obtained, that single measurement is used to access the tables.
B.2 Single Liquid in Contact with All
Trim correction to be applied Corrected volume to be ob- tained directly from vesselÕs calibration tables.
The trim correction is typically applied to the observed sounding to arrive at a trim corrected sounding The trim
corrected sounding is used to enter the vesselÕs calibration tables to obtain the liquid volume.
When applying trim corrections to soundings, it is crucial to exercise caution If these corrections pertain to ullages, the signs "+" or "−" should be reversed when implementing the corrections to the soundings.
It is also acceptable in this situation to enter the vesselÕs calibration tables with a trim corrected ullage.
Alternate 1: On some vessels, the calibration tables are en- tered with the observed sounding and the trim The trim ad- justed volume is then read directly from the table.
Alternate 2: Some trim correction tables provide a volu- metric adjustment that is applied to the volume obtained from the vesselÕs calibration tables using the observed sounding.
B.3 Single Liquid in Contact with Three Bulkheads Only (See Figure B-3)
Wedge table or formula to be used for volume calculation.
If wedge tables are available, they should be used.
Wedge tables are usually entered with the observed sound- ing and the trim Wedge volume is read directly from the table.
In the wedge formula, there are four basic steps to follow:
Step 1: Calculate the adjusted sounding ÒAÓ.
Step 2: Verify the existence of the wedge condition.
Step 3: Divide ÒAÓ by two and extract the table volume
(for this sounding) from the vesselÕs calibration tables.
Step 4: Calculate the wedge volume, which is a function of the table volume obtained in Step 3.
APPENDIX B—CONFIGURATION EXAMPLES AND CALCULATIONS
Figure B-2—Single Liquid in Contact with All Four
To determine the volume of a vessel with a sounding of 0.148 meters while on an even keel and upright, refer to the tank table In this case, the corresponding volume is 379.68 barrels.
Step 4:Calculate the wedge volume as follows:
When calculating volume, ensure that all units of measurement are consistent, using either decimal feet or meters If the table volume is specified in barrels, the final answer will also be in barrels.
The table volume offers a volumetric factor that, when integrated into the overall formula, partially considers the internal tank framing (if present in the vessel's capacity tables), the volume beneath the tank datum, and the tank's width at its lower extremities.
B.3.1 VESSELS TRIMMED BY THE HEAD
For vessels trimmed by the head, the value of ÒUÓ represents the distance from the gauge point to the forward bulkhead, rather than the after bulkhead, as illustrated in Figure B.
3 The calculation for vessels trimmed by the head is termed a reverse wedge. wedge volume = table volume A
EXAMPLE(all units in meters)
Required Field Information Legend Field Data
Distance from Aft Bulkhead to
Trim Factor (trim divided by LBP) F 0.02409
Step 1:Calculate the adjusted sounding ÒAÓ as follows:
Step 2:Verify the existence of the wedge condition Deter- mine the validity of the wedge condition as follows:
If the calculated length is greater than the actual compart- ment length, a wedge condition DOES NOT EXIST.
VesselÕs trim correction is applicable in this situation; re- fer to B.2. length of wedge A
Figure B-3—Single Liquid in Contact with Three Bulkheads Only
B.4 Single Liquid Above Nonliquid (See
Liquid in contact with all four bulkheads.
To obtain the total volume, apply trim correction and refer to the vessel's calibration tables for the corrected volume The observed sounding represented by "XZ" is the relevant measurement for this process.
For nonliquid volume measurement, no trim correction or wedge formula is applicable The volume should be directly obtained from the vessel's calibration tables, with the observed sounding represented by "YZ" being the relevant measurement.
For Liquid Volume: Deduct the nonliquid volume from the total volume.
B.5 Single Liquid Above Nonliquid (See Figure B-5)
Liquid in contact with three bulkheads only.
The total volume is calculated by adding the nonliquid volume to the wedge volume The nonliquid volume can be directly obtained from the vessel's calibration tables, with the applicable observed sounding represented by "YZ" (S YZ).
To calculate the liquid volume of a wedge, use the wedge formula Refer to section B.3 for details, where the sounding indicated by "XY" represents the observed sounding (S = XY) Additionally, adjust the reference gauge height by the value of the nonliquid sounding.
B.6 Two Liquids (Oil and Water) (See Figure B-6)
Both liquids in contact with all four bulkheads.
For total liquid measurement, it is essential to apply trim correction The corrected volume should be directly obtained from the vessel's calibration tables, with the applicable observed sounding represented by "XZ."
For lower liquid levels, apply trim correction and obtain the corrected volume directly from the vessel's calibration tables Refer to section B.2, where the sounding indicated by "YZ" represents the relevant observed measurement.
For Upper Liquid: Subtract the lower liquid volume from the total liquid volume.
It is also acceptable in this situation to enter the vesselÕs calibration tables with trim corrected ullages for the total liq- uid and the lower liquid respectively.
Figure B-4—Single Liquid Above Nonliquid (Liquid in
Contact with All Four Bulkheads)
Figure B-5—Single Liquid Above Nonliquid (Liquid in Contact with Three
S ECTION 4—M ETHOD FOR Q UANTIFICATION OF S MALL V OLUMES ON M ARINE V ESSELS (OBQ/ROB) 9