Will appreciate comments and views on the following:

Background Info:
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1. An offshore production facility (complex), consisting of several platforms has been in

operation for the last 8 months. Among the platforms in this complex are a Central

Processing Platform (CPP) and a bridge linked WHRP Platform (WHRP).

2. The bridge is pinned at one end (CPP side) and is sliding on the end (WHRP side).

3. Our inhouse stress analysis methodology/criteria requires all lines on the bridge to be

stress analysed because of externally imposed movement (bridge movements).The methodology

also requires all hydrocarbon lines to be stress anlysed andthe utility lines, according to the temperatures/line sizes.

4. All the required stress analysis was successfully completed (using Caesar II) during detailed design stage and whatever supports and recommendations implemented, or at least we thought.

5. During a routine inspection service recently, one of our site personnel noticed that almost all the piping expansion loops on the bridge has been restrained severly from movement. On the expansion loops itself, two directional restraints (inverted goal post) have been used. This prevented the expansion loops from functioning properly and there was a cause for concern. We were concerned over the possibility that as a result of the expansion loops beign restrained, the piping could have been overestressed.

6. We checked the design recommendation with what was installed and found that there were some differences between what was actually recommended and what was insatlled at site. There differences include piping routing and the types of restraints used. (the "as-builts" were nto that accurate either.

7. We did a as-built survey and we captured all the details we wanted to do the stress analysis, at least for the main lines runnign across the bridge.

8. After completing the as-built activity, we realised there were no two convenient anchor points located on the either side of the bridge for each line to allow us to quickly model it into Caesar II to get a stress result (using a two-point anchor system).

9. Some lines were anchored on one side with the other running well into the platform facility, until an equipment nozzle anchor is met.

10. For lines (like item 9 above) that run well into platform facility, to our horror, there were many branch lines to it, not to mention sub-branch lines.


The Question/Problem
====================

1. IF we recall, the main issue was the stress condition of the lines on the bridge, which had their expansion loop freedom restrained.

2. To stress every single branch lines/subrnach lines (process hydrocarbon) again will be an intolerably expensive affair.

3. Question: With the fact that all lines have been stress analysed earlier durign detailed esign stage, could we just drop all the branch lines regardless of their size and just stress analysis the main line alone?

4. Question (Related to Item 3): If we could drop the branch lines, is there a general criteria used in the industry? Could we drop all branch lines that are smaller than half the size of the main line (process hydrocarbon and utiltiy lines)?

5. Question (Related to ITem 3): OR should we model the node at the branch connections and limit the displacement such that the branch lines are not affected by excessive movement on the main line? What will be the acceptable discplacement criteria in this case with respect to pipe sizes, service, class rating?

6. Question: For a moment consider a hypothetical case whereby we have dropped all branch lines and we are just left with the main line across the bridge and it is anchored at one end (CPP) and on the other side of the bridge (WHRP) there is none. In this case, how will we able to model this line with just one anchor point?

7. Question (Related to Item 6): Do we need to assume a what is called a Virtual/MAthematical Anchor point? What is the criteria for the selection/modelling of a virtual anchor point in Caesar II? Can we assume that if a main line 4" connects to a line that is at least twice its size, we can assume the t-point as a virtual anchor? Are there any other similar guidelines in the oil and gas industry?


8. Can the same approach be used for the branch and sub-branch lines?

9. Once we have used a virtual/mathematical anchor in the model, do we impose any restraint/limitations to this virtual anchor such that any forces, movements generated at this vuirtual anchor does not get transfered to the other segment of line?

10. General Question: Lastly, has Caesar II any provisions to take into consideration the stress analysis modelling of post contruction work? Note that the as-built dimensions we input will be based on a "stressed/expanded" pipe, not new condition/unexpanded condition.


A million thanks for anyone could throw some light on the above.