Subsea Pipeline Stability Standards Review

1.0           Subsea Pipeline Stability Standards Review

1.1             PETRONAS technical standards - PTS 31.40.00.10

The PTS offer the traditional static analysis.

1.2             British Standard - BS8010-2:2004

Generally, BS8010 follow the DNV RP E305 & DNV OS F101

1.3             ASME\ANSI B31.8

ASME B31.8 recommends the traditional static analysis.

1.4             API recommended practice 1111, 4 Edition, Dec-2009

API use AGA research (PR-178-516 & PR-178-717) for on-bottom stability analysis. The AGA research defines 3 levels for stability analysis.

Level1: static analysis with single airy wave

Level 2: static analysis with wave spectrum and embedment

Level 3: dynamic analysis with random wave kinematics

Level 3 is similar to DNV code. AGA use Lstab software for stability calculations.

1.5             TOTAL General Specification, Submarine pipeline system, GS PLR 100

GS PLR 100 suggests DNV or equivalent codes.

1.6             DNV

DNV published DNV RP E305 in 1988 and considered pipeline stability for static and dynamic and generalized methods. DNV developed this standard in DNV RP F109. DNV commonly used for stability of submarine pipeline

1.7      Conclusion

DNV RP F109 is considered as a best code for stability calculation and this report is based on it.

CALM buoy simulation with two types of chain

12 graph shows the response of buoy with lighter chain and 678 graphs shows it with heavier chain

12 graph shows the response of buoy with lighter chain and 678 graphs shows it with heavier chain

 

12 graph shows the response of buoy with lighter chain and 678 graphs shows it with heavier chain

Tight Flange strange failure

Tight flanges normally are used for connection two pipe under water without welding. Tight flange is locked to pipe by it's gripper and sealed with a internal rubber sealing. below figure shows the typical Tight flange. the gripper and seal are activated by flange bolts while tightening of flanges bolts.

 

please pay attention, tight flange has not been made by oceaneering

 This failure was strange and intricate because Tight flange was hydrotested before using  .

it was unprecedented . tight flange was failed from back side!!!. it was not normal. why ? . the rubber seal was emerged. almost of bolt was broken.

all bolt and nuts have certificate and sample of them was tested. 

 

the stress analysis of tight flange didn't show any failure

tight flange was located in the rupture point of 4 inch pipeline.

 

Up to now, the reason of the failure is unknown.

subsea pipeline crossing support

If two subsea pipeline cross each other then second pipeline to be install with crossing support. crossing support is one of the important component of subsea pipeline. crossing support must be designed according to soil settlement. more over subsea pipeline to be checked against the upheaval and lateral buckling damages. below figures show a crossing support

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Trenching for subsea pipeline

Trenching of three 32" subsea pipeline with 4" piggy backed was done in south pars in 2009

pre commissioning and hydrotest of subsea pipeline

after sending foam pigs and brush pigs gauging plate to be run in subsea pipeline for pre commissioning operation. pigs travel from pig luncher to lay down head. below figure shows the lay down head.

 gauging pig was in health condition. no damage or bend were observed

SPM Fabrication (Buoy, PLEM )

It is a turn table buoy with a sliding PLEM fabrication

Hydrodynamic coefficients calculation for pipeline and riser

anchor clamp & anchor flange design for riser

size: 32 inch
service: sour
flange class : 1500
Design softwares: Catia for modeling & Drafting ; autopipe and ansys for stress analysis 

General Engineering Works

General Engineering Works