Titanium Pipe Certified to ASTM B-862 vs. “Rolled & Welded Plate”
Often vendors offer “rolled and welded plate” in lieu of pipe manufactured and certified to ASTM B-862 Titanium Welded Pipe. There is nothing wrong with rolled and welded plate as long as the buyer understands the difference with it and pipe manufactured to the welded pipe specification. With this knowledge, the buyer can write a purchasing specification that will meet his specific needs. The following is a discussion of the differences that are most important from a user’s perspective and assumes that the user has not specified anything beyond the Grade of Titanium and the pipe size.
- Permissible Variation in diameter – B-862, Table 6 gives the permissible variation in diameter both over and under. Rolled and welded plate pipe should be required to meet this requirement because if it is not specified in the purchasing specification it may prevent proper fit up of fittings or to pipe manufactured to the specification.
- Orality – this has always been problematic with shop made titanium pipe. The same problems cited above apply here.
- Straightness – some criteria should be provided particularly if there is a potential for bowing when welded. B-862 says that a 10-foot straight edge touching on both ends should not have a separation of more than 0.25” at any point.
- Hydrostatic Testing – most fabricators making and offering rolled and welded pipe do not have the equipment to hydro their product. Special plugs are required to hydro plain end pipe and then the ends must be almost perfect to seal. See our charts showing the Maximum Allowable Internal Pressure for testing.) This problem can be overcome if the fabricator is making flanged spools which can be sealed and tested. However, if a leak is found upon testing and the fabricator of the spools is different than the one who made the pipe, there can be issues regarding the repair.
- Weld Quality – B-862 requires a Guided Bend Test or a Flattening Test to check weld quality. This is also a requirement of ASME Section VIII under paragraph UNF-95. It is an important test to insure that the shielding of the weld is working, that the welder’s technique is appropriate and that the shielding gas is correct.
- Wall thickness – this is an area that works both for and against rolled and welded plate. On the positive side, plate tolerances are different than pipe tolerances. The Maximum Internal Pressure could be calculated using UG-27 and made following ASME rules. This may provide an advantage in higher pressure situations. On the negative side, plate may not make pipe that meets the pipe specification or make fit up difficult. For instance, 10” Sch 10S has a nominal wall of 0.165”. This means the lower limit for the wall thickness is 0.144” and the upper is 0.186”. If 3/16” plate is used, its tolerances per B-265 are 0.178” under and 0.212” over. Since plate is rarely rolled to the low side and 3/16” plate is typically over o.200” thick. This pipe may require extra work in fit up to be properly welded. There are other less egregious, but the nominal plate to be used for rolled and welded plate pipe should be specified by the buyer.
- Liquid Penetrant Inspection – this is a supplementary requirement (S1.) A relatively inexpensive test and recommended for consideration if another pipe testing is not performed.
- Radiography – another supplementary option (S2 & S3). S@ is the supplement specified for 100% radiography using X-radiation per UW@-51 in ASME Section VIII. The pipe should then carry the additional marking of “RT” after the specification and grade on the pipe. This would be highly recommended for rolled and welded plate pipe if hydrostatic testing is not going to be done. The specification also provides for “spot radiography”. This would be of limited usefulness for rolled and welded plate pipe where hydrostatic testing is not to be performed.
The following is the suggested ordering information from ASTM B-862.
4.1 Orders for materials under this specification shall include
the following information as required:
4.1.2 Grade number (Section 1 and Table 2),
4.1.3 Nominal pipe size and schedule (Table 1),
4.1.4 Diameter tolerance (see 9.2),
4.1.5 Method of manufacture and finish (Sections 5 and 10),
4.1.6 Product analysis, if required (Sections 6 and 7; Table
1 and Table 3),
4.1.7 Mechanical properties, (Sections 8, 11, 13, 14, and 15,
and Table 4),
4.1.8 Packaging (Section 22),
4.1.9 Inspection and test reports (Sections 18, 19 and 20),
4.1.10 Supplementary requirements
A buyer’s best protection is to specify the ASTM specification. If the vendor comes back offering rolled and welded plate in lieu of pipe to the specification, the items suggested above should be discussed. They may not be critical to the application, but the buyer should know what he is what will be provided.