Piping System

Based on API 570 Code, the definition of pipe is a pressure-tight cylinder used to convey a fluid or to transmit a fluid pressure.

In refinery or chemical plant, jungle of pipes can be found which are connecting the vessels together. Statistic shows that 40 % of total mechanical failures in the units are because of the process piping.

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Figure 1: Example of process piping failure

The in- service inspection code for piping system inspection is API Standard 570. The other API and ASME Code can be used as supplementary information.

ASME B16.5, ASME Section B31.3 and Section I are the specific codes for new construction. However, most of the technical requirements for design, welding, NDE, and materials can be applied to the inspection, rerating, repair, and alteration of in-service piping systems.

ASME PCC-2, NB-23 and API 570 can be used for piping repair.

Piping Inspection

In-service inspection of the piping system covers:

  • Creating a piping inventory list indicating the line number, pipe specification class, rating, schedule, pipe origin location (from) and pipe destination location (to)
  • Creating piping isometric sketches to facilitate inspection and the recording of corrosion monitoring locations (CMLs)
  • Dividing whole unit piping into piping circuits based on process condition and potential degradation mechanism
  • Selecting appropriate NDE techniques for each piping circuit based on the circuit damage mechanism
  • Determination of CMLs points in piping isometric sketches based on the potential for general or localized corrosion and service specific damage mechanisms
  • Determination of piping service class based consequence of failure and instruction stated in API 570 or based on the Risk Based Inspection method.
  • Carry out external inspection for corrosion, leaks, previous temporary repairs, clamps, coating breakdown, insulation damage, vibration, misalignment, pipe support deterioration specifically in touch points and to air to soil interface, pipe hanger distortion or breakage and frizz damage
  • External thickness measurement on CMLs on each piping circuit
  • Corrosion rate calculation based on metal loss in a specific time interval
  • Retirement thickness calculation based on the minimum required thickness and minimum required structural thickness
  • Remaining life calculation based on the available thickness for corrosion and the corrosion rate value
  • Determination of piping circuit inspection interval based remaining life calculation and piping service class
  • Determination of piping inspection interval for non-thinning damage mechanism
  • Making supplementary inspection with the proper NDE method for piping circuits susceptible to creep cracking
  • Making supplementary inspection with the proper NDE method for piping circuits susceptible to environmental cracking from Chloride SCC, Polythionic acid SCC, Caustic SCC, Amine SCC, Carbonate SCC, Hydrogen blistering and hydrogen induced cracking (HIC), etc.

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Figure 2: Example of visual inspection at pipe support

Application of other NDE methods:

  • PEC (pulsed eddy current), LRUT (long range UT), LREM (long range electromagnetics), RT for wall thickness loss, and CUI and neutron backscatter and infra-red thermography for detection of wet insulation
  • MT (magnetic particle), WFMT (wet fluorescent magnetic particle), PT (penetrant testing), EC (eddy current), UT shear wave, AUT (automated UT), TOFD (time of flight diffraction), RT, ACFM (alternating current field measurement), AET (acoustic emission) for investigating cracking
  • Thermography for detection of fouling and hot spots
  • Internal inspection in opened flanges for deposition, corrosion, localized corrosion, erosion, etc.
  • Internal inspection of clad or lined piping for disbanding, bulging and cracking
  • Internal inspection of refractory lined piping for erosion, deterioration of anchors, undercutting of refractory and coke build up behind refractory
  • Flange joint inspection for distortion and leakage and flange face inspection, ring groove and gasket for corrosion, erosion , cracking and mechanical damage
  • Internal inspection of dismantled valve for corrosion, erosion, mechanical damage and cracking
  • Specific attention and internal inspection of critical check valves
  • Inspection of injection points for localized corrosion
  • Inspection of dead legs for corrosion
  • Corrosion under insulation inspection of piping in susceptible temperature (-12˚ to 175˚ C) either by advance NDT or by removal of insulation and making visual inspection

It is important to make an appropriate reporting and report keeping and implement proper system for quick access to the records.


Figure 3: Example of external visual inspection at piping circuit