Chapter 3: Typical Turnaround Inspection of Unfired Pressure Vessels

3.1    Cleaning Inspection

General Cleaning and Purging:

i    Purging by N2 to remove all Hydrocarbon.

ii   Purging by air to remove N2

iii  Water – jet cleaning to remove scale, slug and any solid residues.  (Drying by blowing air)

Extent of Cleaning for Inspection:

i   Preliminary Inspection: The water jet cleaning shall be effective & sufficiently safe enough for human access without totally remove all slug/residue at bottom/lower level of vessel.  Inspection is to observe the pattern of slug/Residue distribution.  If necessary, collect sample for analysis, especially when there is sign of corrosion/erosion.

ii  Detail Inspection : Further water jet cleaning and air blow drying, to ensure all accessible areas are visible clearly by human eyes with torch light. There shall be no more scale/slug/residue to cover-up areas to be inspected. (eg welded joints)

iii Localized Cleaning by Scrapper, Brush & Rag Such cleaning is necessary by Inspection personnel if the locality is suspected of having any surface crack/pit/gouge/groove.

3.2    UPVs : Hydro-test/ Air-test Inspection & Report

i)   Visual Inspection for Leak Detection

Usually H20/Air pressure is lowered and held up for leak detection.  Check for possible leak at all joint-fittings, nozzles/pipes welded to shell, all doublers welded to shell.

ii)  Visual Inspection: Sign of Over Pressure

Due to poor workmanship/carelessness/lack of proper supervision/ miscommunication/instrument fault there is a possibility of “over-pressure”. Check for any buckling/enlargement of pipe/nozzle body, OR, unusual enlargement / out of roundness of vessel shell / header OR any “plastic behavior” of the vessel.

If there is sign of over – pressure, an investigation shall be carried out:-

·         Check the calibration of pressure gauge, pump capability and function ability, HT record, human error (honesty?), and the amount of over pressure.

·         Dimensional check to verify the Diameter, length, Roundness of the vessel and measure the defective area, NDT the defective area for surface crack.

·         Full investigation and meeting and discussion on Rejection OR Acceptance OR Condition Acceptance.

iii) Visual Inspection for Recent Damage

Due to congestion and high mobility of workers with tools and equipment working on the vessels and surrounding area, especially at height, there is possibility of recent damage introduced mechanically on the vessel.  Unskillful fill-up of vessel with H20 may also cause problem. Check for any sign of fresh mechanical damage on vessel surface, nozzle/pipe and attachments, such as dent, gouge, severe scratch…etc OR any unusual movement /disposition of vessel.

iv) Recheck Previously Repaired/Damaged Area.

Due to 1.5 times pressure test, the weaker areas are imposed with unusual high stress, thus fresh crack may develop and propagate from these spots.NDT (UT/DPT/MPI) all the previously repaired/damaged areas to detect crack.  (Crack tip opening fatigue behavior of pit/gouge/groove due to high stress concentration 1.5 x)

v)  Documentation

Shall include items 1,2,3,4 if any and also to include Ht record, pressure gauge calibration record, dead Wt result, damage report and photo (if any).

3.3 Actions and Findings

	Findings	Actions
External And Preliminary Inspection.	*External Surface Defects/ Conditions/damage	*Record in inspection form indicate clearly location.                          Report immediately to                                       Inspection Coordinator
Excessive	*Sludge Accumulations,  Suspicious of pitting	*Record in the Insp. form to be inspected in Detail.                             Recommend Collection of                       Sample for analysis
	Detect Crack	Report immediately to Insp. Coordinator for NDT to    verify crack size & nature
Detail Internal	*Detect severe pitting corrosion	*Measure pit depth and pattern of pitting
	*Suspicious findings	*Report to Insp. Coordinator      for immediate checking and Verification
During and after Hydro-test	*Sign of overpressure	*Report immediately to Coordinator.  Register Investigation
Air Test	*Detect Leak	*Verify nature of leak report In the form.   If leak is due to defect in Pressurized part, request for Investigation

3.3    Record Keeping and Documentation

One does not have to keep good records to start a program and possibly even finish one.  But it is highly likely that somewhere or sometime there will be a need for records that have not been maintained, and a regret that good record keeping was not carried on.  To be sure, too many records can be undesirable.  But a well thought out system of maintaining good cost, design, operating and monitoring records is most helpful in keeping a program running right and headed in a successful direction.

3.4 Reasons for Record Keeping

·         Provide before – after documentation of programs

·         Provide chronological – historical record

·         Support justification to management for projects

·         Document effects of changes in treatment level or method

·         Permit reporting as needed on status and results

Types of Records

1)     Inspection cost records;

·         Leak frequencies

·         Repair / replacement costs

·         Production losses from failures

·         Associated cost – damages, etc.

2)     Inspection program records;

·         Original design bases, data, estimates, forecasts

·         Installation, equipment drawings, plans

·         QA inspection reports, third party reports

·         Vendors invoices, status reports, analyses

·         Treatment records-dates, quantities, types

3)     Inspection;

·         UT, Radiographic reports

·         Metallurgical and chemical analyses

·         Failure / leak frequencies and locations

4)     Computerized record keeping;

·         Databanks can hold large amounts of information and access it quickly

·         Can cut down on the amount of paper to be physically filed

·         Back-up disks are good practice, to prevent loss of records in case of equipment failure.

3.5   Inspection Report

3.5(a)    External Visual Inspection

3.5(b)    Internal Visual Inspection

3.5(c)    Manufacture’s Data Report Form

3.5(d)    Typical Examples of Reports on Problem Vessels                       

SAMPLE OF INSPECTION REPORT

REPORT ON PROBLEM VESSEL	DATE : 22/01/11 PMT NO.:
ITEM NO :	DESCRIPTION : 2ND stage Suction drum
DESIGN PRESSURE : 1310.0 kpag	OPER. PRESSURE : 795.0 kpag
DESIGN TEMPURATURE : 130.0 °C	OPER. TEMPARATURE : 49.0  °C
DESIGN THICKNESS : 14.3 mm	MIN ALLOW. THICKNESS : 8.3 mm
ORIGINAL THICKNESS : 16.7 mm	REMAINING THICKNESS : 14.5 mm
DATE OF INSPECTION : A.    INTERNAL INSPECTION                     B.     EXTERNAL INSPECTION         -  30th. October 2008                                          -  26th February 2008         -  2nd May 2010                                                  -  25th August 2010          - 6th. November 2010                                        -  26th January 2011
FINDINGS : During internal inspection performed on 30th October 2008, signs of erosion and corrosion was detected.  The average metal loss was 3.0 mm.  The internal weld seams was slightly eroded.  At that time the problem was suspected to cause by erosion attack ie. By mill scales in the gas during commissioning. From external ultrasonic flaw detection performed on 26th February 2008, there seemed no additional metal loss and the weld seams were in good condition. On 2nd. May 2010, another internal inspection was conducted.  The condition was getting worsen ie. The vessel was badly eroded and corroded.  The average metal loss was 3.5 mm and the internal weld seams capping were 80% removed. From the internal inspection performed on 6th November 2010, the internal weld seams capping was totally removed.  The average metal loss of the vessel wall remained the same. Result of external ultrasonic flaw detection performed on 26th January 2011 indicated that an average reduction of 0.5 to 1.0 mm in thickness of the vessel wall was detected. (Refer attachment c of appendix I for detail report) Study shows that the cause of the problem was mainly due to very acidic environment in the vessel.  Turbulent flow of the fluid inside the vessel also played a major role for erosion problem. As approved by DOSH, the vessel is due for internal coating.