0027/nd guidelines for Marine Lifting and Lowering Operations

19.11 
RIGID PIPE RISER INSTALLATION 
19.11.1 
This section covers rigid pipe that is to be attached to the exposed parts of a fixed installation resting 
on the seabed, e.g. a steel jacket structure, where the riser is installed in one or more sections (or 
spools) or, in rare cases, attached to the pipeline. 

---

GUIDELINES
 
FOR
 
MARINE
 
LIFTING
 
&
 
LOWERING
 
OPERATIONS 
0027/ND Rev 11 
 
Page 75 of 84 
19.11.2 
Riser spools can vary significantly in length and size. Short spools will be accommodated and 
seafastened on deck by lashings or weldments and clamps as appropriate. Large spools may have to 
be cantilevered or carried on over-side seafastenings welded to the installation vessel or to a transport 
barge. Transportation and seafastening of spools over-side of the vessel is covered in 0030/ND, Ref. 
[5]. Lifting of all but the shortest spools is covered in Section 19.10. 
19.11.3 
Spools with a length to diameter ratio of less than 10-15 need not normally be subject to dynamic 
analysis for the lift and instead may be designed simply with a DAF of 2.0 on the nominal weight from 
the piping and its lifting aids.
19.11.4 
Prior to riser spool lifting, riser support clamps will be installed and adjusted to the geometry of the riser 
using taut wires or laser geometry to line them up. As the geometry can be quite complex, the 
fabricated spool must match the geometry through the clamps within the design tolerance allowed.
The nominal design height from the lowest clamp to the seabed needs to be checked in the field for 
consistency with the design tolerance. 
19.11.5 
Spools will be lifted into place, secured and clamped in a sequence suited to the platform and the 
joining method. Note that codes and standards limit the angular offset and the hi-lo at piping butt 
joints. At flanged joints it is not acceptable to attempt to close flanges which are visibly misaligned 
either torsionally, radially or subtending an angle between their axes. 
19.11.6 
Spool(s) from the lowest clamp to the seabed touchdown, and onward to the joint with the pipeline, are 
normally designed to flex elastically to accommodate platform settlement and pipeline expansion.
Consequently, it is also important that these fit in accordance with the design dimensions and 
tolerances. 
19.11.7 
Lift rigging and lifting aids should normally comply with the requirements of Sections 5 and 19.3.
Lifting points should not be welded directly to the pipe. Note that for long spools there may be a need 
to upend sections to assemble the spool in the field. The lifting design should cover all phases of the 
spool lifting and fabrication operations. 
19.11.8 
The tail of the riser and the pipeline will be moved into alignment for connection. Usually this entails 
lateral movement of the seabed pipeline on H-frames in controlled steps. If welded, the tail of the riser 
and the end of the pipeline will be lifted to welding height in a habitat or cofferdam. If flanged, the tail 
of the riser will be raised a little off the seabed, often on airbags or on an H-frame, to allow access to 
the flange for connection and tightening. All pipeline and riser movements should be analysed for load 
and stress to confirm equipment loadings and that pipe stresses are acceptable and to optimise the 
locations of H-frames, etc., for pipe level and angle at the connection. 
19.11.9 
Once connected, if flanged and already hydrotested, the line will be leak tested; otherwise it will be 
NDT tested and hydrotested. In some particular circumstances a so called “Golden Weld” will be 
permitted which is not required to be strength tested by hydrotest. Codes and Regulators normally 
only permit this where the hydrotest would expose other parts of the system which cannot be isolated 
to unacceptably large stresses or it is not practical to flood and test the pipeline to achieve a hydrotest.
In lieu of hydrotesting, stringent additional NDT is required.
19.11.10 
Leak tests are normally required at or above 1.1 times MAOP (Maximum Allowable Operating 
Pressure) for 4 hours, whereas hydrotest is normally for 24 hours at or above 1.5 times pipeline design 
pressure. The test specification should govern and define the acceptance criteria for any unaccounted 
pressure loss.