Section 15 — Inspection

In-Plant Inspection of Existing Piping Systems

IPE Engineering Practice IPE-EP-15-4-2

Document number: IPE-EP-15-4-2 · Section: 15 — Inspection

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SCOPE

This procedure defines the requirements and specifies responsibilities for the inspection of existing plant process piping.

For the purposes of this Practice, an existing piping system shall be regarded as a piping system that has been installed and has been placed in service.

This document shall conform to all the requirements of applicable codes and standards for the inspection, documentation, and repair or replacement of in–service piping systems.

A revision bar indicates all changes made to this Revision.

REFERENCES

The latest edition of the following standards and publications are referred to herein:

STANDARDS AND PUBLICATIONS

IPE Engineering Practices
EP 5–2–3 IPE Piping Standards EP 5–5–3 Piping Erection and Testing EP 5–11–2 Inspection, Repair, Alteration, and Rerating of In–Service Piping Systems EP 15–3–1 Training, Qualifying and Certifying Personnel for Inspection of Plant Equipment EP 15–4–1 Principles and Practices for Inspection and Testing of In-Plant Equipment
API Standards and Recommended Practices
Std 570 Piping Inspection Code RP 574 Inspection of Piping, Tubing, Valves, and Fittings
ASNT Recommended Practice
SNT–TC–1A Personnel Qualification and Certification in Non–Destructive Examination

DEFINITIONS

For the purposes of this Practice the following definitions shall apply:

Process Piping – Metallic Piping systems that contain process fluids under pressure. Fluids may be, but not limited to, crude oil, intermediate or finished products, hazardous fluids used in the processing of products, and hazardous waste streams. Plant utility and fire protection piping are not included in this definition.

Piping Thickness Monitoring Location (TML) – Designated areas on piping systems where periodic inspections and thickness measurements are conducted.

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INSPECTION PERSONNEL

Personnel performing inspection of process pressure piping shall be qualified according to EP 15–3–1.

Contracted personnel performing nondestructive examination of process pressure piping shall be certified according to ASNT recommended practice SNT–TC–1A. Only Level II or Level III personnel may independently apply nondestructive tests or interpret test results.

PROCESS PIPING CLASSIFICATION

Process piping systems shall be classified into categories for the purposes of establishing maximum visual external inspection and thickness monitoring frequencies.

The classification system shall take into account the hazards associated with the fluid contained in the piping system, and any other factors the Plant Inspection Authority may choose to include.

The classification system chosen by the plant shall be consistent with the requirements of EP 15–4–1.

If the plant does not develop a classification system, the default system shall be the one recommended in API 570.

Certain process piping systems may be exempted from the thickness monitoring requirements of this Practice at the decision of the Plant Inspection Authority and Plant Management, if the requirements in API 570 are met.

PIPING IDENTIFICATION

All process piping requiring inspection shall be contained in inspection documentation that shall provide adequate information to precisely locate and identify the piping within the plant.

To help inspection personnel in locating and identifying piping in the plant, process piping can be shown on isometric sketches or drawings.

The piping shall be identified as to process unit, service, design temperature, design pressure, and piping design classification per EP 5–2–3:

Where the design pressure or design temperature is unknown, the maximum operating pressure and temperature may be substituted since it is identified as such.
Where the piping design classification for existing piping is unavailable, Engineering Services should be notified so one may be developed.

All pertinent piping inspection information shall be shown in inspection documentation, such information shall include:
Component type (pipe, ell, tee, valve, etc.)
Piping connection type (flanged, welded, screwed, etc.)
Piping component sizes (diameter and schedule or thickness).

Each service should be further subdivided into piping circuits that identifies a common corrosive environment. Each circuit shall be uniquely identified for record keeping purposes. Factors to consider in defining a circuit are:
Main fluid flow from one piece of process equipment to another piece of process equipment.
Injection points and associated piping upstream and downstream of the injection point (See API 570 for further definition of injection point circuits).
For mixed phase flow and certain corrosive services, where velocity effects can cause erosion/corrosion, each different piping size can be considered as separate circuits.
Each circuit shall contain the same piping materials except valve internals, orifices, etc.
Within each piping circuit selected for thickness monitoring, TML’s shall be identified. The number and strategic placement depend on several factors. Table 1 may be used to determine a minimum number of TMLs when the inspector does not have sufficient knowledge or experience to determine an appropriate number. The following are some guidelines:
The higher the potential for corrosion, hazard, or risk, the more TML’s may be selected.
Less complex circuits normally require fewer locations than more complex circuits in similar service.
TMLs shall be selected where they are easily accessible to the inspector. Care should be taken to minimize placing locations where scaffolding is required, unless it is necessary to meet other inspection location requirements.
When possible, each dead leg should contain at least one TML.
When possible, TMLs shall be selected where turbulence, changes in flow direction, or changes in velocity may occur.
Where possible, TMLs shall be assigned where two streams join within a piping circuit.
As piping corrodes in a circuit and nears the retirement thickness, additional TMLs may be added to increase the accuracy of the corrosion rate calculations.

EXTERNAL INSPECTION

External visual inspection of piping may be performed while the pipe system is in operation.
Refer to API RP574 section on inspection procedures for detailed discussion regarding items to inspect.
External inspection of insulated piping shall include a program of identifying areas susceptible to corrosion under insulation (CUI) as discussed in API 570. Some guidelines are as follows:
A representative sample of piping in these areas shall be examined for CUI at each external inspection; if any severe corrosion has been found the inspection of piping in this area shall be extended until all the corroded piping has been identified and examined.
Any corroded piping shall be evaluated for integrity and repaired or replaced as necessary.
Piping in areas where CUI has been identified shall be inspected at regular intervals or until the cause of the CUI has been corrected.
The extent of the external CUI inspection program may be adjusted based on the results of previous inspections.

Thickness measurements shall be taken at designated TMLs to monitor the rate of corrosion using either intrusive or non–intrusive inspection methods as practical. Guidelines for taking measurements are as follows:
It is suggested that an inspection plan be developed for use each time thickness readings are taken to define the best method of obtaining the data for each inspection location to be monitored.
When possible, initial readings should be taken when the piping is new to establish the uncorroded thickness of the piping. When initial readings are taken, the area of the TML should be scanned to determine a typical thickness. When it is not possible to take initial readings, the value of the nominal thickness of new, uncorroded piping shall be used.
Subsequent thickness readings should include scanning the entire TML where possible to identify a minimum reading (if profile radiography is used, two films taken at 90o to each other may be needed).
The minimum thickness reading, TML ID number, inspector’s name, measurement method, and date shall be recorded. Any unusual visual observations shall also be noted and recorded.
Where practical, profile radiography may be used to assess the general internal and external condition of insulated piping at the TML. Radiography should be in accordance with the following:
The film shall be of adequate size to provide as much information on the TML as practical.
Thickness measurements may be taken directly from the radiograph using appropriate sizing factors if the value of the thickness reading is sufficiently confident.
If the information from the radiograph indicates unusual conditions, further inspection next to or nearby the TML may be warranted.
Radiography shall be the preferred thickness measurement method for small diameter piping (NPS 1 inch and less).
When using Ultrasonic NDE to measure thickness of selected TMLs:
Where experience/service shows a greater erosion/corrosion concern, accessible pipe elbows shall have ultrasonic thickness scanning made at the outside bend radius at several TML’s.
Accessible tees and branch connections shall have ultrasonic thickness scanning made along the backside of connections (directly opposite the neck of the branch inlet and at adjacent locations) when the fluid flow is from the branch into the main piping.
Accessible reducers shall have ultrasonic thickness scanning taken immediately downstream of the size transition when flow is toward the smaller pipe size.
When monitoring the thickness of insulated piping, access ports, designed to prevent the ingress of moisture under the insulation, shall be installed. These shall then be considered the TML and they shall be placed in areas of the piping circuit where the higher rates of corrosion are anticipated. Profile radiography may be used in initially placing these TML’s.
When scanning a TML with ultrasonic NDE, only the minimum reading need be recorded for thickness monitoring purposes.
When subsequent readings at a TML show a thickness growth outside the precision error of the inspection method, additional readings shall be taken to verify the reading value.

INTERNAL INSPECTION

Where the internal surface of piping including valves and gasket surfaces is accessible to visual examination, internal inspection shall include an examination of all accessible surfaces. Random nondestructive examination for internal corrosion may be used to supplement the inspection. The inspection shall include the following:
Internal pipe surfaces shall be cleaned before inspection, if necessary.
Pipe, pipe welds, fittings, valves, and gasket surfaces shall be inspected for the following conditions:
Localized corrosion, pitting, erosion, and impingement damage.
Blistering.
Cracking.
Refractory lined piping should be inspected for:
Erosion and deterioration of the refractory. In highly erosive service, the refractory thickness should be monitored, where possible, using internal inspection and supplemented with external infrared thermography or similar methods, where practical.
Deterioration of the anchoring system.
Undercutting of the refractory and coke buildup behind the refractory.
Alloy clad or lined piping should be inspected for:
Disbonding of the alloy lining or cladding.
Cracking.
Corrosion or deterioration of the lining.
Bulging or blistering.

RECORDS AND DOCUMENTATION

During all phases of inspection, a pipe system drawing or sketch shall be marked in a way that permits correlation of inspection findings to specific pipe locations.
A system of recording thickness measurements and piping conditions shall be established to maintain the history of each piping circuit and TML.
The minimum thickness measurements shall be used to determine corrosion rates, next inspection dates, and recommended retirement dates for piping which is nearing the end of its useful life.
Computer software, such as PCMS, capable of maintaining inspection information and calculating corrosion rates, inspection dates, and retirement dates may be used.
Inspection histories and corrosion data for each piping circuit shall be reviewed at least annually for timeliness of future inspection or maintenance activities for the piping.

PIPING REPAIR, RETIREMENT, OR REPLACEMENT

When in the judgement of the Plant Inspection Authority, conditions in the piping exist which would render it unfit or unsafe for continued service, the identified piping shall be either

repaired, retired, or replaced. Such conditions include, but are not limited to, the following:

Consumption of the corrosion allowance as determined by engineering calculations or applicable code requirements and identified by the thickness monitoring program.

Excessive pitting that may lead to penetration of the piping wall and result in leakage of its contents.
Sufficient deterioration of the piping material properties as to render it unfit such as graphitization, embrittlement, creep, or hydrogen attack.
Mechanical factors in the piping system that may result in excessive cyclic or steady state stresses beyond code allowances in piping components. Such conditions may arise from excessive piping movement, insufficient pipe support, improper design, etc.
Environmental cracking caused by such substances as caustics, hydrogen sulfide, amines, polythionic acid, chorides, etc.
The piping service life may be extended beyond its allowable limit only if an engineering analysis of the piping verifies that its life can safely be extended. The extension shall be acceptable to and approved by the Plant Inspection Authority. The analysis shall recommend a maximum life extension interval or new minimum wall thickness limit. This analysis shall be documented and included in the piping inspection file.
Whenever possible, piping repair or replacement should be identified with sufficient lead time to allow for a scheduled maintenance outage to do the work.
Temporary and permanent repairs shall be performed and inspected in accordance with the requirements of API 570 and EP 5–11–2.

FINAL INSPECTION

Final pressure tests of the pipe system shall be witnessed and recorded per the requirements of EP 5–5–3.
Before commissioning of the piping, inspection and test results shall be reviewed by and acceptable to the Plant Inspection Authority.

RESPONSIBILITIES

The Plant Inspection Authority or his delegate shall be responsible for:
Evaluating inspection findings, and providing guidance of potential repairs.
The inspection authority shall audit acceptability of inspection and testing results relative to the applicable codes and standards.
The Maintenance Supervisor/Engineer or his delegate shall be responsible for:
Before commissioning, the piping quality control for fabrication and installation shall be reviewed and checked by the installing authority (installer) for completeness and compliance with applicable codes and standards.
Notifying the inspector when a piping system has been opened and flushed, and is ready for possible internal inspection.
Supporting any required operations involving repair or alteration.
Quality Control of the fabrication, installation, and testing of repairs or alterations.
Providing final documentation to the Inspection Authority necessary for review and acceptance.
The Inspector shall be responsible for:
External and internal inspection of the pipe system and components in accordance with this procedure.
Obtaining or supervising the obtaining of thickness measurements.

Positively locating and documenting inspection findings.
Providing report indicating inspection findings and the location of findings when requested.
Recommending repairs and replacements.
Reviewing and accepting the pressure test procedure including the test pressure.
Specifying and marking pipe TML’s that are to receive thickness monitoring.
Notifying and scheduling the Nondestructive Test Technician for performing requested NDE.
The Nondestructive Test Coordinator shall be responsible for:
Specifying and marking pipe locations that are to receive tangential or weld radiography.
Notifying the Nondestructive Test Technician of the need for performing radiography.
The Nondestructive Testing Technician shall be responsible for:
Performing UT thickness measurements or producing tangential radiographs of TML’s that have been identified as requiring measurements.
Producing radiographs or performing ultrasonic flaw detection of weld repairs or replacement welds when required in accordance with approved procedures.
Providing radiographic film interpretation or ultrasonic test results and reports to the assigned inspector.

13.0 TABLES

TABLE 1

RECOMMENDED MINIMUM NUMBER OF TML’S FOR PIPING CIRCUITS	RECOMMENDED MINIMUM NUMBER OF TML’S FOR PIPING CIRCUITS	RECOMMENDED MINIMUM NUMBER OF TML’S FOR PIPING CIRCUITS	RECOMMENDED MINIMUM NUMBER OF TML’S FOR PIPING CIRCUITS
FACTORS	LOW<–––––––––––––––SEVERITY–––––––––––––––>HIGH	LOW<–––––––––––––––SEVERITY–––––––––––––––>HIGH	LOW<–––––––––––––––SEVERITY–––––––––––––––>HIGH
COMPLEXITY	Mostly straight run piping. No more than two non– flanged fittings. Add 1 TML	Default Add 2 TML’s	Complex piping. Eight or more non–flanged fittings. Add 3 TML’s
EXPECTED CORROSIVITY	Slightly corrosive. Less than five mpy Add 1 TML	Default Add 2 TML’s	Highly corrosive. Greater than 10 mpy, or susceptible to severe pitting. Add 3 TML’s
CONSEQUENCE	Non–toxic or short term toxicity with no long term effects, and with low flammability. Add 1 TML	Default Add 2 TML	Lethal toxicity, or potential for vapor explosion. Add 3 TML
LOCATION	Offsite and remote from personnel exposure. Add 0 TML	Default Add 1 TML	Within unit boundaries and within 30 feet of personnel quarters. Add 2 TML’s

Note: This table is used by selecting the appropriate value in each of the four rows to determine the recommended minimum number of TML’s for a circuit. Assume initially 0 TML’s and add the number of TML’s indicated in each box selected.

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