1. PURPOSE
1.1 This engineering specification defines requirements for welding of adjustable mounting plates to both the fully extractable cold box valve body extension tube and the cold box panel.
2. SCOPE
2.1 This specification applies to the installation of fully extractable cold box valves that are provided by the valve manufacturer with an adjustable mounting plate. The adjustable mounting plate slides along the valve body extension tube.
3. RELATED DOCUMENTS
3.1 None
4. BACKGROUND
4.1 Fully extractable valves are provided with adjustable mounting plates to allow for cold box manufacturing tolerances. The valve is designed with a fixed dimensional extension length from the centerline of the valve body to the top of the mounting plate (MP). The cold box is designed by using the fixed dimension as the design basis. The intention of the adjustable mounting plate is to allow for manufacturing tolerances such that the fixed design dimension can vary 13 mm (1/2 in) in length and also allow several degrees tolerance in the mounting angle.
4.2 Welding of the mounting plate to the valve body extension tube and the box panel does require care. This procedure is provided for the following purposes: To define mounting plate positioning and alignment To define mounting plate variability along the valve body extension tube To define mounting plate weld tack placement To define mounting plate welding requirements To avoid weld overheat of the valve extension tube To avoid distortion of the valve extension tube inner diameter
4.3 Fully extractable valves with adjustable mounting plates might be designed and furnished with a collar or an integral lip along the extension tube. The collar or integral lip is provided to assist in avoiding weld overheat effects to the extension tube inner diameter.
5. MOUNTING PLATE POSITIONING AND ALIGNMENT
5.1 The adjustable mounting plate is provided by the valve manufacturer and freely slides along the valve extension tube. The mounting plate should be located per dimension “E” shown in Figure 2. However, due to manufacturing tolerances, the mounting plate location might vary from the “E” dimension. The variance shall not exceed 13 mm (1/2 in) above or below the “E” dimension. The manufacturing tolerances are present when the valve is installed with pre-spooled piping.
5.2 Positioning the mounting plate for tack welding requires that a consistent gap be attained between the MP inner diameter and the valve body extension tube. The proper gap is attained by positioning the MP in a horizontal position when the valve is installed at an angle of 25 degrees above the horizontal (Figure 2) and when the mounting plate major axis is aligned vertically. Locating the mounting plate major axis in a vertical orientation is critical to achieving a consistent gap, since the inner diameter has an elliptical bore. The word “TOP” is stamped on the mounting plate to help locate the major axis of the mounting plate. The cold box fabricator shall place scribe marks on the major and minor axes on the mounting plate, and on the circular box panel penetration. The scribe marks can assist in lining up the mounting plate with the box panel.
5.3 Spacer shims may be used to maintain mounting plate clearance in preparation for tack welding. The average clearance between the MP elliptical inner diameter and the valve body extension tube should average 1.5 mm (1/16 in) for valve sizes DN80 (NPS 3) and below and 2.5 mm (3/32 in) for valve sizes DN100 (NPS 4) and DN150 (NPS 6).
6. TACK WELDING
6.1 Once the mounting plate positioning and alignment are established, tack welding of the mounting plate to both the box face and valve body extension tube is recommended, to maintain plate positioning in preparation for fillet welding.
6.2 The MP shall be tack welded to the box face panel, prior to tack welding the MP to the valve body extension tube. Tack welding shall be on the exterior side of the box for the box panel weld. A tack weld shall be placed every 25 to 38 mm (1 to 1 1/2 in) apart for the MP to box face panel. There shall be eight button tack welds, equally spaced, for the MP to valve body extension tube. All tacking welds shall be button style, and each tack weld shall be 5 to 6 mm (3/16 to 1/4 in) long. See Figure 1 for details.
6.2.1 The button tacks with 25 to 38 mm (1 to 1 1/2 in) spacing is required to avoid MP distortion and waviness.
7. MOUNTING PLATE FILLET WELDS
7.1 Mounting plate welds are required for the inner diameter weld to the valve body extension tube and the box panel weld to MP outer diameter area. The outer diameter shall be seal welded on the box exterior.
Figure 1 Mounting Plate Button Tack Detail
7.2 The mounting plate inner diameter weld to the valve extension tube may be performed either on the inside or the outside of the cold box. The inside box weld is necessary when clearances are small as a result of the mounting plate being close to the extension tube flange. The small clearance is present for valve sizes DN100 (NPS 4) through DN150 (NPS 6). Thus for valve sizes DN100 (NPS 4) through DN150 (NPS 6), the inner diameter weld shall be performed inside the cold box. Valve sizes DN50 (NPS 2) and below have acceptable space to allow the inner weld to be performed on the exterior side of the box.
7.3 The cold box fabricator shall evaluate the final clearance between the top facing of the mounting plate and the tube extension flange to determine the optimum location of the inner diameter weld (inside or outside of cold box).
7.4 The inner diameter mounting plate fillet weld shall be performed prior to the box panel fillet weld. This sequence is desired to avoid plate distortion on the inner diameter. Care shall be exercised in avoiding weld overheat, thereby preventing distortion to the valve body extension tube inner diameter.
7.5 The box panel weld to mounting plate weld is equally important to avoid distortion to the mounting plate inside diameter and inner diameter of the valve extension tube. When performing the panel fillet weld, care shall be exercised in controlling heat to avoid overheat.
7.6 The mounting plate will incur discoloration at the inner diameter weld. After welding, the discoloration shall be wire brush cleaned while the mounting plate is still warm.
7.7 When the inside diameter fillet weld is performed on the inside of the box, a bead of white silicon sealant shall be applied on the box exterior along the circumferential interface between the valve extension tube and MP inner diameter. This shall be done to avoid entrapment of moisture.
7.8 Fillet welds shall have a 3 mm (1/8 in) effective throat. The filler material for the mounting plate (stainless steel) to valve body extension tube (stainless steel) weld shall be ER308, 3/32 inch diameter. Filler material ER309 3/32 inch diameter shall be used for the bimetallic mounting plate to box panel (carbon steel) weld.
7.9 Since the fillet welds serve as an anchor and seal for the cold box purge gas and perlite insulation, these welds are critical. The MP inner diameter weld might require a second pass as determined by the cold box fabricator. Should a second pass be required, the weld pass shall be performed only after all welding is complete. Weld heat input shall be at a minimum to avoid overheat and weld distortion.
8. TIG WELD
8.1 Welding shall be performed by a qualified welder in accordance with a qualified ASME welding procedure specification. The gas tungsten arc (TIG) process shall be used to perform the subject weld.
9. INSTALLATION PREFERENCE
9.1 Valve installation may be either mounted to the box panel as a stand-alone component or be part of the pre-spooled piping. The preference is to mount the valve to the box panel as a stand-alone component to precisely achieve the desired extension length (dimension “E”) and the 25 degree angle. The adjustable mounting does accommodate manufacturing tolerances to allow the valve to be installed with pre-spooled piping.
9.2 The preferred stand-alone mounting sequence is as follows: Align mounting plate major axis Tack weld mounting plate to the box panel Rotate valve to position in proper flow direction Slide valve body extension tube to the “E” dimension Align valve at 25 degree angle Tack weld mounting plate to the valve body extension tube Follow welding procedures indicated in Sections 7 and 8. The pre-spooled piping would be welded to the valve at a later time.
9.3 The installation method is at the preference of the cold box fabricator.
10. MOUNTING PLATE INSTALLATION DETAIL
Figure 2 Mounting Plate Installation Detail (Cold Box)
Note: See Table 1 for dimensions
Table 1 Valve Dimensions
| Body Size | Y | E | MD | D Buried Depth |
| DN (NPS) | ||||
| 15 (1/2) | 534 (21) | 441 (17 3/8) | 200 (7 7/8) | 400 (15 3/4) |
| 20 (3/4) | 534 (21) | 441 (17 3/8) | 200 (7 7/8) | 400 (15 3/4) |
| 25 (1) | 534 (21) | 441 (17 3/8) | 200 (7 7/8) | 400 (15 3/4) |
| 40 (1 1/2) | 534 (21) | 441 (17 3/8) | 200 (7 7/8) | 400 (15 3/4) |
| 50 (2) | 534 (21) | 441 (17 3/8) | 200 (7 7/8) | 400 (15 3/4) |
| 80 (3) | 534 (21) | 441 (17 3/8) | 300 (11 13/16) | 400 (15 3/4) |
| 100 (4) | 534 (21) | 441 (17 3/8) | 300 (11 13/16) | 400 (15 3/4) |
| 150 (6) | 686 (27) | 585 (23) | 400 (15 3/4) | 530 (20 7/8) |
Note: Typical each column, mm (in)