1. PURPOSE
1.1 This global fabrication and erection specification defines the requirements for the longitudinal alignment of distillation columns and boxes containing distillation columns during shop or field fabrication.
2. SCOPE
2.1 This specification applies to all distillation columns regardless of type (for example, bubble cap, sieve tray, or packed), diameter, height, process (for example, air separation or HYCO), or material of construction (for example, aluminum, stainless steel, or 9% nickel).
3. RELATED DOCUMENTS
3.1 Air Products Engineering Documents None
4. TOLERANCE CLASSIFICATIONS
4.1 The tolerances are intended to achieve optimum operating efficiency and economy in fabrication.
4.2 Tolerances are classified according to the source of their necessity.
4.3 “M” tolerances are set by mechanical considerations only. Components not complying with these tolerances may only be used on a variation note basis, subject to the vessel engineer’s approval.
4.4 “MP” tolerances are set by mechanical considerations but have some impact on the process. If a “MP” tolerance is not met for a component part, then a “P” tolerance may be exceeded on final assembly. Components not complying with these tolerances may only be used on a variation note basis subject to the vessel engineer’s approval. The vessel engineer’s approval shall only be given when compliance with the “P” tolerance can be ensured.
4.5 “P” tolerances are set solely by process criteria. Components not complying with such tolerances shall be subject to review and approval by a process manager.
5. ASSEMBLY OF COLUMN SHELL SECTIONS IN THE HORIZONTAL (see Figures 1A and 1B)
5.1 A column section is defined as one or more shell courses (strakes) that have been welded together. The section shall have column internals installed, whose level has been transferred to reference points at the section ends.
5.2 The dimensions from two independent datum lines to the reference points near the top and bottom of each section shall simultaneously not exceed 1.25 mm per 1 M of length between the reference points up to a maximum value of 12 mm. This is classified as an “MP” tolerance.
Note: The independent datum lines shall be orientated at right angles to each other. One of the datum lines will normally be opposite the loading (shipping) face.
6. ALIGNMENT OF COLUMN WITHIN THE COLD BOX (see Figure 2)
6.1 The column shall be installed in the cold box such that one of the following is true:The difference in dimensions from plumb lines attached to two adjacent faces of the cold box, to the reference points near the top and bottom of the datum lines used in paragraph 5.2, simultaneously, do not exceed the value provided in paragraph 6.2. This method is normally used by Air Products Europe (AP-E). The difference in dimensions from the reference points near to the top and bottom of each datum line used in paragraph 5.2, to a plumb line stretched between lugs attached to one face of the cold box, simultaneously, do not exceed the value provided in paragraph 6.2. This method is normally used by Manufacturing Design Engineering in the United States.
6.2 The maximum difference in dimensions shall not exceed 3 mm. This is classified as an “MP” tolerance. An inspection check sheet for alignment of columns within cold boxes is provided in Appendix A.
7. SETTING TOLERANCES FOR COLUMN ALIGNMENT DEVICES
7.1 Leveling Targets (Bull’s Eyes) (see Figure 3), when specified, are fixed to the completed column in the horizontal position, such that the maximum difference between the target centerlines and the previously set up datum lines (see paragraph 5.1) do not exceed 3 mm. This is classified as an “MP” tolerance.
7.2 For column sections that are shipped to the field for final assembly (that is, not a completed column), the leveling targets shall be applied to each section while in the shop. The tolerance for application of these targets is 3 mm from shop assembly datum lines used during fabrication of the section. This is classified as an “MP” tolerance.
7.2.1 As each section is aligned and joined in the field, three criteria must be met:
1) Angular alignment of the sections relative to one another (see paragraph 7.2.2).
2) Linear alignment/leveling of each section and the overall column (see Figures 1A and 1B).
3) Critical spacing of column internals at each section joint (as detailed on column GA drawing).
7.2.2 Angular alignment (orientation) of the column sections shall be accomplished and documented using quarter markings on each shell course as primary targets, and leveling targets (bull’s eye) locations as secondary. Alignment to these targets shall be within +/- 6 mm.
7.3 Top head leveling bosses (see Figure 4) are set with the completed column in the horizontal position such that the maximum difference in measurements between the boss bolt heads and a laser beam swung perpendicular to the longitudinal datum lines (paragraph 5.2) do not exceed 1 mm. This is classified as an “MP” tolerance.
Note: The use of leveling bosses is not recommended, as they do not give the same level of accuracy as the other methods. This leveling method is no longer used and is mentioned here for historical purpose only.
8. INSPECTION
8.1 The column alignment and alignment within the cold box shall be checked by an Air Products manufacturing inspector or approved representative. Any deviations from this specification shall be forwarded to the vessel engineer for review.
9. RECORD OF MEASUREMENTS
9.1 All measurements made relating to Sections 5, 6, or 7 shall be recorded by the Air Products inspector or approved representative. The records will be retained by Air Products.
Figure 1A Alignment of Individual Column Sections in the Horizontal
Linear alignment tolerances (to be satisfied simultaneously): |A1-A2|, |A3-A4| ≤ lesser of 6 mm and (1.25a) mm |B1-B2|, |B3-B4| ≤ lesser of 6 mm and (1.25b) mm |A1-B2|, |A3-B4| ≤ lesser of 12 mm and (1.25c) mm a, b, and c are distances between reference points in meters.
Figure 1B Alignment of Assembled Column Sections in the Horizontal (Typically 3 sections – HP Column, Reboiler, LP Column)
Figure 2 Alignment of Columns within Cold Boxes
b) With two box plumb lines
Figure 3 Setting Column Leveling Targets (Bull’s Eyes)
Figure 4 Setting Column Leveling Bosses
NOTE: This method is obsolete and is shown for historical purposes only.
Appendix A Alignment of Columns within Cold Boxes – Inspection Check Sheet
| Air Products Order number |
| Cold box reference |
| Supplier |
| Location |
| Contact |
| Inspection / visit date |
Alignment measurements according to Air Products specification 4WMA-007017
| Box Plumb line arrangement | SINGLE / DOUBLE |
Measurements to column datum line at right angle to loading face
| X1 dimension at bottom of cold box | mm |
| Y1 dimension at top of cold box | mm |
| Deviation = | X1 – Y1 | | mm |
| Allowable deviation (Section 6) | 3 mm |
| Within tolerance ? | YES / NO |
Measurements to column datum line OPPOSITE loading face
| X2 dimension at bottom of cold box | mm |
| Y2 dimension at top of cold box | mm |
| Deviation = | X2 – Y2 | | mm |
| Allowable deviation (Section 6) | 3 mm |
| Within tolerance ? | YES / NO |
Supplier Certification: Measurements by (block capitals) signature
Air Products Representative:Witnessed/checked by (block capitals) signature