M/T Stolt Gulf Mishref

                     Report after inspection carried out 24.01.2015

Prepared by Konrad Klimiuk (Ship Design)

Report based on materials collected during inspection of ship “Stolt Gulf Mishref”  carried out 24.01.2015 on the Atlantic Ocean next to Cape Town. 

Purpose of the inspection:

1. Visual inspection of eventual cracks 
2. Investigation of deformation reason
3. Proposal of modifications to reduce risk of cracks.

Ad.1.  Visual inspection of eventual cracks 

 

1. Existing arrangement of cargo manifold.

 

Pipe manifold “Stolt Gulf Mishref”

In order to cover all cargo tanks pipes on the manifold has been designed in two levels – lower and upper.

 

Part of cargo manifold (PS-aft part)

        Lower level                                                     upper level

1. Condition of the manifold in day of inspection.

From pipes of lower level only CT1S PS has no deformation at all (green mark). On all others some deformations were observed (red marks = magnificent, green+red = medium)

From pipes of upper level CT2S PS and SB has no deformation at all (green mark), same CT10P. On all others deformations were observed (red marks = magnificent, green+red = medium)

1. Pressure test.

Test has been carried out in the presence of Igor Begishev (chief engineer), Alexey Povaligev (chief officer).

Due to specification of cargo located in tanks manifold pipes were divided into two groups:

• 7C, 10C, 9P : tested by nitrogen : pressure 2-2,5 bar
• All other : tested by air : pressure 6-6,3 bar

 

1. Visual assessment using foam.

 

No leakages were observed on the surface covered by foam.

1. Pipe integrity verification using crack detector (3 sprays: cleaner, penetrant, developer).

Due to lack of time only one pipe CT7C PS worst deformed has been chosen to analysis.

 

Pipe CT7C PS prepared to test by paint removal and cleaner applying.

 

Pipe CT7C PS after developer applying

 

Pipe CT7C PS – Crack observed

After crack was observed pressure in the verified pipe has been increased to 6 bar of nitrogen and foam test was carried out once again. No leakages appeared.

 

1. Conclusions of pressure test.

No leakages were observed but superficial crack next to place where support has been welded to pipe can prove bad condition of tested pipe in the most critical place.

Taking into account that almost all cargo pipes lying on manifold has been deformed in similar way (see p.1.2 of this report), and cause of deformation has not been excluded  risk of damage during future cargo operation can be significant.

Ad.2. Investigation of deformation reason

2.1. Support arrangement.

 

Manifold pipes lies on I-beam tightened by u-bolt with two nuts and with sliding pad below (see sketch below). At the ends (PS, SB) fixed supports were designed.

sliding support

    fixed support

 

2.2. Cargo operations and cleaning operations as well are carried out in the temperature up to 80 deg.C . 

Line expansion factor for stainless steel 316 L, a= 16,5 x 10 (-6) 1/K

 

Final length of pipe X = 

 

X = X0 (1 + a delta T) where : X0 – length in reference temperature 20 deg.C

X0 = 21.000 [mm]

a – line expansion factor [1/K]

delta T – temperature rise                   (60 deg.C)

 

X = 21.000 (1+0,0000165×60)

X = 21.0207 [mm]

Expansion of manifold pipe during operation in temperature 80 deg. C is about 20 mm.

In such conditions pipe moves on sliding supports in axial direction and  stops on fixed at the end.

As a result of axial movement bending moments appear in place where pipe is blocked.

2.3. Conclusions.

It has not been found any indications to support previous suspicions of overloading cargo manifold lines by cargo hoses or loading arms.

In such case deformation would be visible on outside part of support.

Based on building specification documents  mentioned pipe is :

150A : 165,2 x 3,4  Material 316 L.

That sort of pipe is not durable enough to transfer bending moment through I-beam element to opposite side of support and generate deformation in red color area. 

The expected deformation area in overloading scenario has been presented at sketch above in blue color. 

 

Moreover sliding pad is not destroyed what would be unavoidable to transfer bending moment in overloading scenario.

Also type of damage of I–beam (pushed out to outside) confirms thermal expansion theory.

 

 

Ad.3. Proposal of modifications to reduce risk of cracks.

1. Supports

As soon as possible fixed supports should be removed completely. 

All U-bolts has to be adjusted in such way to keep 1 mm distance to pipe by using distance nut first and than lock nut. Teflon strap to be install between pipe and u-bolt. This will create proper sliding support and enable pipe to expand.

Currently on board all U-bolts are clinched with no distance at all.

 This fact increased the problem and makes up the reason of pipe deformation apart from fixed supports at the ends.

 

1. Pipes.

Pipes are arranged as butt welded. So it is not possible to replace one spool. There must be cut off 1-1,5 m piece of pipe and weld new one.

1. I-beam construction (first pipe rack from presentation flange).

It is recommended to replace construction with the new one. Corrosion is very intensive, distortion and rusty holes  are visible in many places.