In certain parts
of the world it is highly relevant to use spiral welded pipes for offshore
applications. This is driven by cost, project characteristics and the desire to
manufacture the pipe close to where it is to be used. Spiral welded line
pipe has been used extensively for onshore applications, however there has been
some reluctance to specify spiral welded line pipe for offshore
applications. A joint industry project is beeing carried out together with
coil manufacturers, pipe manufacturers, installation contractors and
operators to review the status regarding offshore applications for spiral
welded pipes and identify the most critical technology gaps using a technology
qualification process. Detailed suggestions as to how the gaps can be met
have been made. An update on efforts to close these gaps is ongoing.
The challenges
for spiral welded line pipe include design, metallurgical and quality control
issues. The design issues include fracture arrest, collapse and
displacement controlled loading conditions which are all highlighted in DNVs
standard for submarine pipelines (DNV OS F101). The design issues
regarding load controlled displacement are mainly due to
limited experience with spiral welded line pipe subjected to large
strains. For running fracture the limited experience with spiral welded
pipe for offshore applications is an issue.
There are 5 new
spiral welded pipe mills in United States so availability has improved. The
review includes an assessment of typical pipe material test results and
whether properties required for offshore applications can reasonably be
expected.
Det Norske Veritas (U.S.A.), Inc. (DNV) and MCSKenny are carrying out a joint industry project (JIP) to investigate the suitability of spiral welded pipe for offshore applications. It appears that the industry has a general understanding that the performance of spiral welded (SAWH) pipes is different to Submerge Arc Welded (SAWL)/ High Frequency Welded(HFI)/ Electric Resistance Welded ERW linepipe when exposed to the same loading conditions, and that currently existing design standards for offshore applications may not be applicable. An important issue is to establish how the spiral wound linepipe can be produced consistently to a high level of quality, and what is required by the design standard for spiral welded pipe to be fit for purpose for offshore use. Some of the main areas of concern regarding the quality of spiral wound linepipe will be discussed. The aim is to assess whether SAWH linepipe can be considered equivalent to SAWL and HFI/ERW linepipe.
The use of
spiral welded linepipe (SAWH) for pipelines has generally been the most popular
manufacturing choice of linepipe for onshore low pressure pipelines, pipelines
transporting water, ship borne piping, or very shallow waterlow pressure pipelines
(≤ 500 ft). Recently there has been more interest in the use of spiral
wound linepipe, due to the following reasons:
- SAWH linepipe is a cost-effective solution compared to the other manufacturing processes.
- Generally, the chemical compositions, mechanical properties and dimensional tolerances are assumed to be comparable to SAWL pipe.
- SAWH linepipe can be manufactured in 80 ft lengths with diameters from 20 to more than 100-inch OD and wall thicknesses ranging from approximately 9 to 25 mm.
- Some SAWH pipe mills have coating capabilities for 80 ft pipe lengths (FBE and 3-layer coating systems). 80 ft pipe lengths could mean less fabrication costs for the installation contractors.
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