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Epoxy Sleeve Repair

How it helped a fertilizer plant in saving a shutdown

One of the Fertilizer’s Plant Main Gas supply line got severe corrosion problem on almost 12ft area inside a valve pit due to accumulation of stagnant water in the pit. Water remained accumulated for months & months because of no surveillance and resulted in damaging the wrapping as well as initiating & propagating severe corrosion issue which resulted in a pinhole leakage as well as thickness loss below the pressure design thickness. The pinhole leakage was temporarily addressed by using a clamp. However, since the thickness of line was below PDT (Pressure Design Thickness), therefore it was absolutely necessary to repair the defected/corroded portion of line either by replacing it with new one or by welding sleeves over the corroded portion. Schematic of Inspection findings carried out after leakage is given below:

Schematic

Fig. 1 Schematic of Inspection Findings

Fig.1Fig2Fig3

Fig. 2 Severe corrosion observed during inspection and installation of clamp on pinhole

The corroded portion of line was located in a very sensitive central Manifold of Gas well & online welding on pressurized (600psig) Gas Line was a safety risk. Therefore, permission of welding was to be sought from well owners as the repair work was to be carried out in the Battery limit of Gas Well. Keeping in view the sensitivity of location, a thorough repair strategy was developed by gathering API guidelines, standards as well as neighboring industries’ practices to build some confidence of well owners on hot repair. Unfortunately, the well owners did not allow the Fertilizer industry to weld sleeves on Gas line in pressurized condition as if any burn thru during welding would lead to catastrophic devastation of entire facility and insisted to shut down the line & replace the defected portion. Despite of welding sleeves on available healthy locations, well owners were not convinced because they were not having any prior experience of online welding on pressurized Gas lines where as it was practiced regularly on need basis in the fertilizer industry as well as in neighboring industries.

Thickness readings taken adjacent to corroded areas were well above the minimum required for in-service welding (see Fig. 3). API 2201 and ASME PCC-2 were followed as guidelines for minimum required thickness.

Thickness

Fig. 3 Thickness readings adjacent to corroded areas (well above minimum as per API 2201)

Shutting down the line for repair was actually shutting down the down-stream Fertilizer plant for almost 3~4 days of time; costing business & economic loss to the company. Since, at that time frame, there was an unbalanced situation for urea supply & demand in the market – supplies being at the lower side & demands on higher side warranted uninterrupted Fertilizer plant operation in the Country.

As they say: Where there is a will there is a way

Continuous struggle & objective of carrying out repair without shutting down the plant became possible when a cold repair technique was found being in use by many Oil & Gas industries in different countries across the globe. The repair they named as Epoxy Sleeve repair”.


All technical specifications were gathered, networking with different industries was done to authenticate the repair applications. After completing ground works, mock up testing of repair technique was carried out to testify/qualify the repair method as well as to give confidence & sought approval from well owners. For mock up testing a 15 ft long pipe spool was taken & thickness of pipe reduced form original 9mm to 2 mm on almost 1ft area & 02 EA thru holes of 1mm dia were also drilled. Epoxy repair was made & after curing (24hrs time) it was subjected to a hydrostatic test pressure at 1000 psig for 30 min without any leakage / pressure drop. The mock up testing of repair was successful & gained full confidence of our management as well as the management of well owners. Now they were convinced for this cold repair to be carried out on-stream. Afterwards, corroded areas of Gas line were safely secured by using Epoxy Sleeve repair technique. The repair remained successful & helped saving a plant shutdown. Stage wise application of Epoxy sleeve repair is given below:

Picture Gallery

CS
Material
CS Split Sleeves after fabrication
Epoxy material mixing (base & hardner)
Step 1: Cleaner Application (bottom figures)
s1
s2
Pipe after Cleaner Application
Pipe surface after dry out of cleaner
Step 2: Epoxy application
s3
s4
Step 3: Epoxy Application on Sleeve ID
s5
s6
Step 4: Sleeve Placement & Torquing
s7
s8

 

Key aspects to be considered for Epoxy Sleeve repair

1. Applicability to non-leaking situations only
2. Thickness of split sleeve shall be equivalent to the original pipe thickness.
3. Number of bolts for sleeve shall be evaluated based on experience.
4. Approximately 4~6mm gap shall be left for Epoxy fill up between pipe O.D & sleeve ID.
5. Pipe Surface shall be thoroughly cleaned & if practical sand/grit blasted.
6. Sleeve prepared for carrying out ESR shall be Grit blasted from ID.
7. Length of Split sleeve shall not be extended beyond 1.5 ft to enable easy handling. Multiple sleeves shall be fabricated if the repair area is more than 1.5ft.
8. After application of Epoxy layer on repair area, sleeves shall be positioned & Torque on sleeve bolts shall be applied till excess epoxy material moves out from sleeve ends.  
9. The excess material moved out at sleeve edges shall be tapered to form a cold circumferential fillet joint which ensure perfect sealing.

Cost comparison of different repair options

Cost Analysis - Different Repair Methods for Pipeline

Method

Production Loss

Pipe Line Cost

Consumables

Sleeves/Fabrication

Workforce

Total Cost

 

USD

USD

USD

USD

USD

USD

Pipe Line Replacement Cost

1650602

505.92

12.21686747

Nill

180

1651300

Sleeve Welding Cost

Nill

Nill

12.21686747

600

90

702

Epoxy Sleeve Repair Cost

Nill

Nill

4000

600

450

5050

 

Comparison with other cold repair techniques

Fields

Furmaniting

Relative Comparison

Remarks

Plidco Clamp
(PC)

Composite Repair
(CR)

Epoxy Sleeve Repair
(ESR)

Safety

Excellent

Excellent

Excellent

Excellent

No hot work involved in all 4 cases

Reliability

Good

Good

Fair

Excellent

Mechanical Keying of epoxy with base metal makes ESR tough & becomes load bearing piping component.

Performance

Good

Excellent

Good

Excellent

ESR /Plidco repairs give excellent life

Pressure Strength

Good

Excellent

Good

Excellent

ESR pressure tested upto 3000psig - Lehigh Testing Laboratories USA

Fabrication

Fair

Fair

Excellent

Good

Plidco clamps require special design & Fabrication experties

Life

Good

Good

Fair

Excellent

ESR is considered as permanent repair.

Cost

6000 $

36000$

1000$

5700$

Composite repair is the cheapest with less reliability

Timeline

7 weeks

10Weeks

2 Weeks

1 week

Plidco clamps lead time - 10weeks , ESR-7 days

 

Lessons learnt

Just a small negligence of letting the water inside valve pit created such a big problem & could have led to plant shut down & have caused loss of Millions. Below are few learning’s from this incident.
1. All the valve pits shall be made water proof.
2. A system shall be instituted for regular surveillance of such valve pits.
3. Regular cleaning of Valve pits / drainage of rain water shall be ensured.   
4. Regular thickness check up of lines inside pits shall be done

       
 
NAQ
Nabeel Ahmed Qureshi
B.Sc Metallurgy & Materials Engineering, Working as Inspection Engineer with Engro Fertilizers Limited since 2007. Major expertise are in the field of Inspection, Materials,Welding & corrosion.

 

 
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