1.3.3 Shipping
For most pressure vessels, the cost of shipping is not more than a few percent of the total cost, yet even that is enough that it should be considered in the price of the product. For products that are extremely large or extremely heavy, however, that percentage may increase.
The size and load capacity of standard rail cars facilitate shipment of many vessels that might require permits as wide, long, or heavy loads if shipped by truck. Rail rates (per pound) are often much less than truck rates. Barges even more so, if the size of the product justifies them. This is especially the case if permits or special routing are needed for trucking. Rail shipments often take longer than trucks, however, due to the way that rail traffic is routed.
In any case, unless the estimator is confident of knowing shipping costs with a good degree of accuracy, it would be good to verify costs with shippers prior to bidding a job. See Chapter 11 for more information regarding shipping.
1.3.4 General approach to cost control
Effective management of cost involves making trades based on actual costs of the delivered product. It therefore requires assessment not only of material and labor costs but also the cost of shipping. This will be especially important for shipment of large and/or heavy fabrications. These are likely to require permits and may require special equipment and routing, raising costs far above the usual cost per pound for shipping.
A general rule, with some exceptions, is that labor costs outweigh material costs and that labor is therefore the area most ripe for cost reductions.
If, for example, material represents 10% of the cost of a product, then any reduction in material costs must clearly be less than 10% of the cost of the overall product. This could be the case for a carbon steel vessel with complex fit‐up. For this, vessel reductions in labor likely do not increase material costs significantly and should be considered as ways of reducing overall costs.
A vessel fabricated of certain nickel alloys, titanium, or zirconium, on the other hand, will have very high material costs. In this situation, reducing material costs may be effective in reducing overall costs.
Seeking only the lowest hourly rates risks, at times, finding the lowest productivity, but where skilled labor is acquired cheaply, overall product costs may be low.
Thus, it is important to assess the overall cost of a delivered product. When a design change is made, whether or not with the intent of reducing costs, overall costs must be reassessed. It will sometimes be found that the change results in even greater savings than anticipated, but it will also sometimes be found that the savings are eaten up by increases in other areas.
1.4 Fabrication of Nonnuclear Versus Nuclear Pressure Vessels
The fabrication of nuclear components such as vessels, pumps, valves, piping, and storage tanks in the United States must meet the requirements of Section III Division 1 of the ASME Boiler and Pressure Vessel Code as well as the rules of the U.S. Nuclear Regulatory Commission (NRC). This book is written for nonnuclear applications. While the general fabrication processes such as forming, machining, and welding are the same for both nonnuclear and nuclear components, the quality control process is different regarding the details of these operations.
Nuclear components constructed in accordance with the ASME code are considered in “classes” that are used to construct pressure equipment in accordance to its relative importance to safety. The three most common classes are Class 1, 2, and 3.
Class 1 components, including vessels such as reactor vessels, pressurizers and the primary side (tubes) of steam generators are exposed to radioactive coolant fluid, and they consequently are considered to bear the highest importance to safety. Class 1 vessels therefore require the most stringent levels of quality control for the various fabrication operations, compared to Class 2 and 3 vessels. Class 2 vessels generally resemble ASME VIII‐2 (editions prior to 2007) requirements, while Class 3 components are generally similar to VIII‐1 requirements.
All three classes of nuclear components are subject to strict quality control during construction. Quality assurance requirements for nuclear applications are provided in Article 4000 of the ASME Nuclear Code Subsection NCA (General Requirements for Division 1 and Division 2), along with its references to ASME NQA‐1 (Quality Assurance Requirements for Nuclear Facility Applications, Part I and Part II).
Some of the details required during fabrication of Class 1 nuclear vessels, pumps, valves, and piping are as follows:
1 All materials must be provided with documentation showing Certified Material Mill Test Reports. The location of the test specimens taken from the mill plate must be identified for traceability. When a piece of the mill plate is cut out for use as a vessel part, its location in the mill plate is recorded and identified. Depending on the material, the method of removing the plate, such as machining or burning then grinding, may need to be recorded. The type and identification number of the grinding wheel may also need to be recorded. These requirements must be met for each piece of material in the pressure vessel.
2 Hot forming during fabrication must be qualified and documented. The effect of hot forming on material properties and final thickness for some materials may have to be recorded.
3 All weld electrodes and wires must be identified, including recording of heat numbers, location where used, and properties, with full documentation and traceability.
4 Each weld in the vessel must be identified with regard to the location as well as WPS and PQR.
5 All weld repairs on materials and welds during fabrication must be identified and documented. Such documentation must include weld procedures and their effect on properties such as strength and impact values.
6 Examination of welds and components must be documented.
7 Records of operators, equipment used, calibration of equipment, and results of tests must be maintained.
This limited sample of Class 1 requirements illustrates the extent to which quality control and documentation required for nuclear components exceed those for nonnuclear components.
1.5 Units and Abbreviations
This section describes the unit conventions used in this book. Consistency of units is important in communicating technical data. While throughout the engineering field there is generally good comprehension of units, conversions, and their use, various industries and companies have their own conventions. This can result in confusion, mistakes, and accidents. An example is when NASA lost a 125‐million‐dollar Mars Climate Orbiter when the navigation team at JPL used the customary NASA metric units in its calculations of acceleration readings while Lockheed Martin that built the spacecraft provided the vital acceleration data in the English units. And as the Los Angeles Times put it, “In a sense, the spacecraft was lost in translation.”
Rates will use abbreviations, not followed by a period, and a slash rather than “per.” Example: “inches per minute” will be written as “in./min”, and in metric “mm/min.”
While in machining the cutting speed is generally referred to as “surface feet per minute,” for consistency with other sections this will be written as “ft/min” with no periods at the ends of the abbreviations.
“Micro” will be represented by the lowercase Greek letter mu, written as μ.
English units will be used, followed by the metric equivalent. Dimensions will generally be rounded when converted, and will show no more than three significant figures. For example, “6 in.” becomes “150 mm.” This convention will be followed unless something is clearly intended as an exact dimension or for nominal sizes that are clearly not rounded measurements of the specified dimension. Thus, 6 in. plate is written as 150 mm, and 6 in. pipe is written as DN 150. 3/4 in. plate is written as 19 mm plate.
Appendix