Introduction: Understanding Welding & Fabrication in Piping – A Guide for Freshers
Welding and fabrication are two of the most essential processes in the piping industry, especially in sectors like oil & gas, refineries, petrochemicals, and power plants. As a fresher engineering graduate preparing for job interviews, having a basic understanding of these concepts is not just helpful—it’s necessary.
Fabrication involves the cutting, bending, and assembling of pipes, fittings, and supports according to engineering drawings like isometrics or GADs. This is where raw materials are transformed into usable piping systems.
Welding is the process of joining metal parts together using heat or pressure. In piping, it ensures strong and leak-proof connections that can handle high pressures and temperatures.
Even if you’re applying for a general piping or mechanical role (not directly in welding), interviewers often ask questions related to:
- Basic welding processes (like SMAW, GTAW, etc.)
- Welding procedures (WPS, PQR, WPQ)
- Common welding defects and how to detect them
- Basic fabrication techniques and industry standards (ASME, API, etc.)
👉 In this article, I’m going to share some basic yet important interview questions and answers related to welding and fabrication that every fresher should know. These will help you understand the practical side of piping work and give you an edge in interviews—especially in the oil & gas and construction sectors.
Let’s begin with the fundamentals and build your confidence step by step. 💪
Q- What are the different weld layers in piping welding?
Answer:
Weld joints in piping are completed in multiple layers to ensure strength, quality, and proper fusion. The main weld layers are:
- Root Pass
- This is the first weld layer applied to the joint.
- It ensures full penetration and fusion at the root of the joint.
- Critical for weld strength and leak-proof performance.
- Hot Pass
- Applied immediately after the root pass.
- Removes slag and smoothens the root to avoid defects.
- Helps in bonding the root to the upcoming fill passes.
- Fill Pass
- Multiple passes added to build up the weld joint thickness.
- Fills the remaining groove space.
- Provides structural strength to the joint.
- Cap Pass (Capping)
- Final layer that completes the weld.
- Provides a neat finish and reinforces the weld.
- Must be smooth, uniform, and free of defects like undercut or overlap.
🔧 Note: The number of fill passes may vary depending on pipe thickness and welding procedure.
Q- What is the accepted misalignment in piping weld joints?
Answer:
Misalignment refers to the offset between the internal surfaces of two pipes or fittings being welded together. It should be within acceptable limits to avoid stress concentration, poor weld quality, and flow restriction.
Accepted misalignment limits are:
- 1.5 mm – As per ASME B31.3 (Process Piping Code)
- This is the general tolerance for high-integrity process piping systems.
- It ensures proper alignment for safe operation and smooth fluid flow.
- 1.6 mm – As per ASME Section IX (Welding Qualification Code)
- This standard applies to welder qualification and welding procedure qualification.
- Slightly more lenient, as it’s used during test coupons rather than installed piping.
🔍 Note: Actual permissible misalignment may also depend on pipe diameter, wall thickness, and specific project/client requirements. Always refer to approved drawings and project specifications for exact tolerances.
Q- What is the meaning of ITP (Inspection and Test Plan)?
Answer:
ITP stands for Inspection and Test Plan.
It is a formal document that outlines the step-by-step inspection and testing activities to be carried out on a product, system, or component during manufacturing, fabrication, or installation.
🔍 Key points about ITP:
- Describes what will be inspected or tested (e.g., materials, welds, dimensions, pressure tests).
- Lists the type of inspection (e.g., visual inspection, dimensional check, NDT, function testing, FAT).
- Specifies when and how the inspection will take place during each stage of the project.
- Defines the roles and responsibilities of all parties involved (contractor, client, third-party inspector).
- Ensures quality control and compliance with applicable codes, standards, and project specifications.
🧾 Typical inspections covered in an ITP:
- Raw material inspection
- Fit-up and weld visual inspection
- Dimensional checks
- Non-destructive testing (RT, UT, PT, etc.)
- Pressure testing (Hydro/Pneumatic)
- Final acceptance inspection or Factory Acceptance Test (FAT)
✅ Purpose: ITP ensures that all inspections and tests are planned, documented, and performed correctly to maintain consistent product quality and safety.
Q- What are the four types of inspection stages in quality control? Explain with meaning.
Answer:
In quality control and assurance processes, there are four standard inspection stages that define the level of involvement and responsibility of the QA/QC team during different inspection or testing activities.
These stages are as below:
1. Hold Point (H):
- A mandatory inspection stage.
- Work must stop until the QA/QC representative is present.
- Inspection or testing cannot proceed without approval from QA/QC.
- The contractor must notify in advance and wait for QA/QC presence.
- Used for critical inspections, such as hydrostatic testing or final visual weld inspection.
✅ Example: Hydrotest should not begin unless the QA/QC inspector is present and gives clearance.
2. Witness Point (W):
- QA/QC must be informed in advance about the inspection or test schedule.
- However, work can proceed even if the QA/QC representative does not attend.
- The activity will still be conducted as scheduled.
- QA/QC may choose to attend or skip the inspection.
✅ Example: Fit-up inspection before welding – QA/QC may witness or review later.
3. Surveillance (S):
- QA/QC conducts routine or random monitoring of the work in progress.
- No prior notice is needed from the construction team.
- Ensures continuous quality without disrupting workflow.
- Helps identify issues early during fabrication or erection.
✅ Example: QA/QC walks into the fabrication yard and observes welders during their daily work.
4. Review (R):
- QA/QC team reviews and approves documents related to quality and inspection.
- Includes reviewing WPS, PQR, WPQ, NDT reports, calibration records, and test certificates.
- Ensures all documentation is in line with project specifications and codes.
✅ Example: Reviewing NDT reports or welding documentation before final handover.
📌 Summary Table:
| Inspection Stage | Description | QA/QC Presence Required? |
|---|---|---|
| Hold Point | Must stop until QA/QC approves | Yes (mandatory) |
| Witness Point | QA/QC informed, but not mandatory to attend | Optional |
| Surveillance | Ongoing monitoring without notice | Not required in advance |
| Review | Document checking and approval | Yes (off-site or on-site) |
Q- What are ‘Specifications’ in piping and construction? Explain.
Answer:
Specifications are detailed written documents that define the technical requirements, construction guidelines, and minimum quality standards for materials, equipment, and workmanship to be followed during a project.
They serve as a reference guide for engineers, contractors, inspectors, and construction teams to ensure that all work meets the design intent, client expectations, and industry codes/standards.
📋 Key Features of Specifications:
- Describe materials to be used (type, grade, class, etc.).
- Define installation methods and construction procedures.
- Specify testing and inspection requirements.
- Set acceptance criteria and tolerances.
- Mention applicable codes and standards (like ASME, ASTM, API, etc.).
- Ensure uniformity and quality assurance across the project.
📌 Purpose of Specifications:
- To provide clear guidance to all teams involved in construction or fabrication.
- To ensure compliance with safety, reliability, and functional standards.
- To serve as a legal and technical document in case of disputes or clarifications.
✅ Example:
A piping specification may state that:
- All carbon steel pipes must be ASTM A106 Grade B,
- Welds must be inspected as per ASME Section V,
- and all flange connections must meet ASME B16.5 standards.
🔍 In simple words: Specifications are the rulebook that ensures construction is done correctly, safely, and to the required quality level.
Q- What is P&ID (Piping and Instrumentation Diagram)?
Answer:
P&ID stands for Piping and Instrumentation Diagram.
It is a detailed engineering drawing that shows the complete piping layout along with instruments and equipment involved in a specific process system.
It is used in design, construction, commissioning, and maintenance of process plants such as refineries, petrochemicals, oil & gas, and power plants.
📋 What does a P&ID show?
A P&ID includes:
- Pipes and Branches
- Reducers and Expanders
- Valves (Gate, Globe, Ball, Control valves, etc.)
- Fittings (Elbows, Tees, etc.)
- Process Equipment (Pumps, Vessels, Exchangers, Reactors, etc.)
- Instrumentation (Pressure gauges, Temperature indicators, Flow meters, etc.)
- Control loops and interlocks
🎯 Purpose of P&ID:
- To give a clear representation of the process flow and control.
- To help in equipment layout, piping design, and safety reviews (like HAZOP).
- To serve as a reference for construction, testing, and maintenance.
- To assist operations and troubleshooting of the plant.
✅ Example:
A P&ID will show a pump connected to a pipeline, controlled by a pressure control valve, with instruments like pressure transmitter (PT) and temperature indicator (TI) connected to the control system.
🔍 In simple words: A P&ID is the roadmap of a process plant — it shows how everything is connected and how the system is controlled.
Read Complete P&ID article and download PDF
Q- What is WPS (Welding Procedure Specification)?
Answer:
WPS stands for Welding Procedure Specification.
It is a formal written document that outlines the detailed welding process and parameters to be followed by the welder to produce quality welds that meet applicable code requirements (like ASME Section IX).
📋 Purpose of WPS:
- To provide clear guidance to the welder or welding operator.
- To ensure the weld is sound, safe, and meets quality standards.
- To maintain consistency and repeatability in welding processes.
- To comply with project specifications and relevant codes.
🧾 A WPS typically includes:
- Type of welding process (SMAW, GTAW, MIG, etc.)
- Base metal and material grade
- Filler metal and electrode details
- Preheat and post-weld heat treatment (PWHT) requirements
- Welding position (1G, 2G, 5G, etc.)
- Joint design and thickness range
- Welding current, voltage, and travel speed
- Shielding gas (if applicable)
✅ Example:
A WPS may specify welding a 6mm thick carbon steel pipe using the SMAW process with E6010 electrode for the root pass and E7018 for fill and cap, in the 5G position.
🔍 In simple words: A WPS is like a recipe for welders—telling them exactly how to perform the weld correctly and safely.
Q- What is PQR (Procedure Qualification Record)?
Answer:
PQR stands for Procedure Qualification Record.
It is a formal record of a test weld that has been performed and tested under controlled conditions to verify that the welding procedure (WPS) will produce a sound and reliable weld that meets code requirements.
A WPS cannot be used in production until it is qualified and supported by a valid PQR.
📋 Purpose of PQR:
- To validate that the welding procedure defined in the WPS can produce acceptable welds.
- To document the actual welding variables used during the test weld.
- To ensure code compliance (e.g., ASME Section IX, AWS D1.1).
🧾 A PQR typically includes:
- Details of the test weld (material, thickness, joint type, etc.)
- Welding parameters actually used (current, voltage, travel speed)
- Type of filler metal and shielding gas
- Position and technique used
- Test results (e.g., tensile, bend, impact, hardness, macro/micro examination)
- Inspector’s certification and approval date
✅ Example:
If a company develops a new WPS for welding stainless steel pipes, they must perform a test weld as per the WPS, conduct mechanical testing, and then record the results in the PQR. Only after successful testing can the WPS be used in actual work.
🔍 In simple words: A PQR is the proof that a welding procedure works—it is the backbone that supports the WPS.
Q- What is WPQ (Welder Performance Qualification)?
Answer:
WPQ stands for Welder Performance Qualification.
It is a certificate or document that proves a welder’s ability to perform a specific welding procedure correctly and in compliance with code requirements, such as ASME Section IX or AWS D1.1.
It confirms that the welder has the skills, knowledge, and hands-on capability to produce sound welds as per the approved Welding Procedure Specification (WPS).
🎯 Purpose of WPQ:
- To verify that the welder is qualified to perform welding using a particular process, material, thickness, and position.
- To ensure weld quality and safety in production.
- To comply with code and project specifications.
🧾 WPQ includes details such as:
- Welder’s name and ID number
- Welding process (e.g., SMAW, GTAW)
- Material type and thickness range
- Welding position (1G, 2G, 5G, 6G, etc.)
- Type of joint (butt, fillet, groove)
- Type of test performed (visual, radiography, bend test, etc.)
- Date of qualification and validity period
✅ Example:
If a welder successfully performs a 6G pipe welding test using GTAW, and the test passes visual and radiographic inspection, they are issued a WPQ certificate qualifying them for similar welds in production.
🔍 In simple words: WPQ is a license or certificate that proves a welder is skilled and qualified to do a specific type of weld on the job.
Q- What is the difference between Pipe and Tube?
Answer:
While pipes and tubes may look similar, they are used for different purposes and are measured differently in engineering and fabrication.
📌 Key Differences Between Pipe and Tube:
| Feature | Pipe | Tube |
|---|---|---|
| Identification | Identified by NB (Nominal Bore) | Identified by OD (Outside Diameter) |
| Thickness | Measured by Schedule (e.g., SCH 40, SCH 80) | Measured by BWG (Birmingham Wire Gauge) or mm |
| Purpose | Mainly used for transporting fluids and gases | Used for structural and mechanical applications |
| Dimensional Tolerance | Less strict tolerance | More precise dimensions and tighter tolerances |
| Shape | Mostly circular | Can be circular, square, or rectangular |
| Measurement Example | 2” NB Pipe (Nominal size, not actual OD) | 50.8 mm Tube (Actual OD) |
🧾 Explanation:
- A pipe is generally used in piping systems to carry liquids or gases and is designed based on pressure and flow rate.
- A tube is used in structural applications, instrumentation systems, or heat exchangers, where exact outside diameter and strength are more important.
✅ Example:
- A 2-inch pipe has an actual OD of 60.3 mm, and thickness varies based on the schedule.
- A 2-inch tube has an OD of exactly 50.8 mm, and the wall thickness is defined in BWG or mm.
🔍 In simple words:
- Pipe is for flow – sized by inside diameter (NB).
- Tube is for structure/precision – sized by outside diameter (OD).
Note: tubes are commonly used for heat transfer applications.
✅ Explanation:
In heat exchangers, boilers, condensers, and cooling coils, tubes are preferred over pipes because:
- Tubes have precise outer diameter (OD) and uniform wall thickness, which is essential for efficient heat transfer.
- They are available in smaller sizes with tighter dimensional tolerances, allowing for compact and optimized designs.
- Tubes can be made from high thermal conductivity materials like copper, stainless steel, and brass, which improve heat exchange performance.
🧪 Examples of heat transfer applications using tubes:
- Shell and tube heat exchangers – Tubes carry one fluid while the shell carries another, allowing heat exchange across the tube wall.
- Boiler water tubes – Carry water or steam for heating.
- Condenser tubes – Used in power plants and refrigeration systems.
- Finned tubes – Used to increase surface area and enhance heat transfer.
🔍 In simple terms:
Tubes are widely used in heat transfer systems because their precise dimensions and material options make them ideal for efficient thermal performance.
Q- What are the main duties of a Piping Inspector?
Answer:
A Piping Inspector plays a crucial role in ensuring that all piping activities—such as fabrication, installation, inspection, and testing—are performed according to project specifications, international standards (like ASME B31.3), and approved procedures.
Below are the main duties and responsibilities of a piping inspector:
🔍 1. Material Receiving & Inspection
- Verify material grade, size, quantity, and heat numbers.
- Ensure materials comply with approved Material Test Certificates (MTCs).
🧊 2. Storage & Preservation
- Ensure proper storage to avoid damage or corrosion.
- Confirm that caps are placed on pipe ends and materials are stored as per procedure.
✂️ 3. Cutting, Assembly & Fit-Up Inspection
- Check marking, cutting methods, and fit-up before welding.
- Verify root gaps, edge preparation, and alignment.
🔧 4. Pre-Welding Inspection
- Ensure correct WPS, welder qualifications (WPQ), and electrode storage.
- Check interpass temperature, cleanliness, and preheat requirements.
👁️ 5. Visual Inspection of Socket & Threaded Joints
- Check for proper engagement, thread sealant, and fitment.
💨 6. Pneumatic Test for Reinforcing Pad
- Witness leak tests on reinforcement pads (pads around branch connections).
🧼 7. Pickling & Passivation
- Inspect chemical cleaning of stainless steel pipes to remove weld burns and contamination.
💻 8. Database Reporting & Documentation
- Record inspection results, test reports, and daily progress in the quality database or logbook.
🔍 9. Visual Inspection of Completed Spools
- Ensure completed pipe spools meet drawing dimensions and have proper weld quality.
🏗️ 10. Piping Pre-Inspection & Spool Erection
- Inspect correct orientation, supports, and spool placement during installation.
🔎 11. Orifice Flange Inspection
- Ensure correct installation of orifice plates and pressure taps, with the flow direction clearly marked.
📐 12. Pipe Support Inspection
- Verify support type, spacing, clamps, and anchor points as per drawings.
📏 13. Verification of Slope
- Check slope in sloped lines (e.g., drain, vent, or process lines) using spirit levels or lasers.
🧽 14. Internal Cleanliness
- Confirm pipes are free from dirt, debris, rust, or welding slag before closing or hydrotesting.
🔩 15. Valve Installation
- Ensure valves are installed in correct orientation and accessible for operation.
🧯 16. Flange Joint Inspection
- Check gasket type, bolt tightening sequence, and surface finish.
📋 17. Pre-Test Punch Listing
- Generate punch list of incomplete items before pressure testing.
💧 18. Hydrostatic or Pneumatic Testing
- Witness testing as per approved test packs and verify test pressure, hold time, and leak check.
🚀 19. Pre-Commissioning Activities
- Ensure systems are cleaned, flushed, and preserved before handing over to operations.
🔍 In simple words:
A piping inspector ensures that all piping activities are done correctly, safely, and as per specifications from material delivery to final testing and commissioning.
Q- How many types of gaskets do you know? Explain briefly.
Answer:
Gaskets are sealing materials or elements placed between two flange faces to prevent leakage of fluids or gases under pressure. They are selected based on pressure, temperature, fluid type, and flange design.
Here are the commonly used types of gaskets in piping systems:
🔹 1. Full Face Gasket (Asbestos / Non-Asbestos)
- Covers the entire flange face, including the bolt holes.
- Typically used in low-pressure systems and flat face flanges.
- Asbestos gaskets are now mostly replaced by non-asbestos alternatives due to health concerns.
🔹 2. Spiral Wound Gasket (Metallic)
- Made of alternating layers of metal windings and soft filler material (like graphite or PTFE).
- Used in high-pressure and high-temperature applications.
- Provides excellent sealing and recovery properties.
- Commonly used with raised face flanges.
🔹 3. Ring Type Gasket (RTJ – Ring Type Joint)
- Solid metal ring used in Ring Type Joint flanges (RTJ flanges).
- Suitable for very high-pressure and high-temperature environments.
- Commonly used in oil & gas, refinery, and offshore industries.
🔹 4. Metal Jacketed Gasket
- Consists of a soft filler (like graphite) enclosed in a metal jacket.
- Offers the benefits of both metal and soft gaskets.
- Used in heat exchangers, high-temp piping, and special applications.
🔹 5. Inside Bolt Circle (IBC) Gasket / Raised Face Gasket
- Covers only the sealing surface inside the bolt holes (inside bolt circle).
- Commonly used with raised face flanges.
- Requires proper alignment to avoid leakage.
🔍 In simple words: Gaskets come in different types to match the flange type, pressure, and temperature of the system. Choosing the right gasket is critical for leak-proof and safe operations.
Q- How are gaskets classified based on materials? Explain with examples.
Answer:
Gaskets are also classified based on the material they are made from, which determines their chemical resistance, temperature limit, pressure handling, and application suitability.
Below are the main categories of gaskets based on materials:
🔹 1. Non-Metallic Gaskets (Soft Gaskets)
- Made from compressible materials like rubber, graphite, PTFE, CNAF (Compressed Non-Asbestos Fiber), etc.
- Used for low to medium pressure and temperature applications.
- Provide excellent sealing where flanges are not perfectly smooth.
Examples:
- Asbestos (now mostly replaced due to health risks)
- Non-asbestos fiber gaskets (CNAF)
- Rubber gaskets (Neoprene, EPDM)
- PTFE (Teflon) – for chemical resistance
- Graphite – suitable for high temperature up to 500°C
✅ Common Use: Water, air, oil, chemicals in low-pressure pipelines
🔹 2. Semi-Metallic Gaskets
- A combination of metal and soft sealing materials.
- Provide a balance of strength and flexibility.
- Suitable for medium to high pressure and temperature.
Examples:
- Spiral wound gaskets – made with stainless steel and graphite/PTFE filler
- Metal jacketed gaskets – soft filler inside a metallic cover
✅ Common Use: Heat exchangers, pressure vessels, high-temp piping
🔹 3. Metallic Gaskets (Hard Gaskets)
- Made entirely from metal such as stainless steel, Inconel, Monel, or soft iron.
- Used in high-pressure, high-temperature, and critical services.
- Require RTJ (Ring Type Joint) flanges with precise surface finish.
Examples:
- RTJ (Ring Type Joint) gaskets – R-type, RX, and BX designs
- Solid metal gaskets for specialized sealing
✅ Common Use: Refineries, offshore platforms, petrochemical plants
📌 Gasket Material Selection Depends On:
- Operating pressure and temperature
- Type of fluid/gas (corrosive, flammable, toxic)
- Flange face type (RF, FF, RTJ)
- Required sealing performance and durability
🔍 In simple words:
Gasket materials range from soft non-metallics (like rubber or graphite) to strong metallic types. The right material ensures leak-proof joints in various pressure, temperature, and chemical environments.
Q- What are the different types of mating flanges? Name and explain the 4 most common types.
Answer:
Mating flanges refer to the two flange faces that come into contact and are bolted together with a gasket in between to form a leak-tight joint.
The type of flange face determines the gasket type, sealing surface, and pressure class compatibility.
Here are the 4 most common flange face types used in piping systems:
🔹 1. Flat Face (FF) Flange
- The entire face of the flange is flat.
- Requires a full-face gasket.
- Commonly used in low-pressure systems and where the mating flange is made of cast iron or plastic.
✅ Used in: Water lines, firefighting systems, and utility services.
🔹 2. Raised Face (RF) Flange
- The sealing area is raised slightly (1.6 mm or 6.4 mm) above the bolt circle face.
- A gasket is placed only on the raised face area, reducing gasket contact area and improving sealing under pressure.
- Most common flange type in process and industrial piping.
✅ Used in: Oil & gas, petrochemicals, power plants.
🔹 3. Ring Type Joint (RTJ) Flange
- Has a machined groove on the flange face for a metallic ring gasket.
- Provides a metal-to-metal seal for very high-pressure and high-temperature services.
- Requires precise installation and special RTJ gaskets.
✅ Used in: Offshore, refineries, high-pressure lines.
🔹 4. Tongue & Groove (T&G) Flange
- One flange has a raised ring (tongue), the other has a matching depression (groove).
- The gasket is seated inside the groove, providing self-alignment and better gasket retention.
- Helps avoid gasket blow-out in moderate to high-pressure systems.
✅ Used in: Heat exchangers, high-integrity joints, critical fluid lines.
🔹 Other Mating Flange Face Types (Less Common):
🔸 Male & Female (M&F) Flange
- Similar to T&G, but the male face is flat and protrudes, and the female face has a recess.
- Gasket sits in the female part for accurate alignment and sealing.
- Used in systems where repeated disassembly is not common.
📌 Comparison Table:
| Flange Face Type | Gasket Type Used | Pressure Rating | Key Feature |
|---|---|---|---|
| Flat Face (FF) | Full Face Gasket | Low | Simple, flat contact |
| Raised Face (RF) | Ring Gasket | Low to High | Most common, good seal efficiency |
| RTJ | Metallic Ring Gasket | Very High | Metal-to-metal seal |
| Tongue & Groove | Special T&G Gasket | Medium to High | Prevents gasket blowout |
| Male & Female | Confined Gasket | Medium | Self-aligning faces |
🔍 In simple terms:
The type of flange face determines how the gasket seals and how strong and leak-proof the connection is under different pressure and temperature conditions.
Q- What are the different types of flanges based on construction?
Answer:
Flanges are also classified based on how they are constructed or connected to the piping system. Each type of flange is selected based on pressure, temperature, pipe material, and service conditions.
Here are the most commonly used flange types based on construction:
🔹 1. Weld Neck Flange (WNF)
- Has a long tapered neck that is butt-welded to the pipe.
- Provides excellent strength, stress distribution, and is suitable for high-pressure, high-temperature applications.
- Commonly used in critical process piping.
✅ Used in: Refineries, chemical plants, high-temperature lines.
🔹 2. Slip-On Flange (SOF)
- The pipe is inserted into the flange and fillet-welded on both the inside and outside.
- Easier to align but less strong than weld neck flanges.
- Suitable for low to medium pressure applications.
✅ Used in: Water lines, cooling systems, fire-fighting systems.
🔹 3. Socket Weld Flange (SWF)
- Has a recessed socket where the pipe is inserted and then fillet welded.
- Commonly used for small diameter, high-pressure piping.
- Provides good strength but not as strong as weld neck flanges.
✅ Used in: Hydraulic systems, steam lines, chemical processing.
🔹 4. Threaded Flange (Screwed Flange)
- Has internal threads and is screwed onto the pipe without welding.
- Suitable for low-pressure, non-critical services where welding is not possible.
- Not recommended for high temperature or vibration-prone lines.
✅ Used in: Utility lines, water supply, compressed air systems.
🔹 5. Lap Joint Flange (LJF)
- Used with a stub end; the flange itself is not welded to the pipe.
- Allows rotation for easy alignment of bolt holes.
- Suitable for systems where frequent disassembly is required.
- Low-pressure use only.
✅ Used in: Food processing, pharmaceutical, and systems with exotic materials.
🔹 6. Blind Flange (BLF)
- A solid disk with bolt holes, used to close the end of a pipe, valve, or equipment.
- Can be easily removed for inspection or future expansion.
- Can handle high-pressure due to solid construction.
✅ Used in: Line terminations, testing, future expansions.
🔹 7. Orifice Flange
- Special flange pair with tap holes for installing an orifice plate and measuring flow.
- Comes with pressure tap ports for pressure drop monitoring.
✅ Used in: Flow measurement systems in process industries.
📌 Summary Table:
| Flange Type | Welding Method / Connection | Pressure Rating | Common Use |
|---|---|---|---|
| Weld Neck | Butt weld | High | Critical process piping |
| Slip-On | Fillet weld (inside & outside) | Medium | Water lines, utility systems |
| Socket Weld | Fillet weld (only outside) | High (small bore) | Small-diameter high-pressure |
| Threaded | Screwed (no welding) | Low | Non-critical low-temp systems |
| Lap Joint | Used with stub end | Low | Easy disassembly |
| Blind | No pipe (end closure) | High | Line isolation |
| Orifice | With orifice plate & taps | Medium–High | Flow measurement |
🔍 In simple words:
Flanges are chosen based on how they connect to the pipe (welding, threading, or bolting) and what pressure or service condition they must handle.
Q- What type of information do you get from Isometric Drawings?
Answer:
An Isometric Drawing is a piping fabrication and installation drawing that represents a 3D view on a 2D paper, showing all necessary details of a pipeline section.
It is widely used in construction, inspection, and fabrication because it provides complete technical information about the piping line in a simplified format.
📋 Key Information Provided by an Isometric Drawing:
🔹 1. Line Routing and Orientation
- Shows the exact path the pipe takes in three dimensions (horizontal, vertical, inclined).
🔹 2. Northing, Easting & Elevation
- Indicates the coordinates and pipe elevation levels to match the actual site layout.
🔹 3. Bill of Materials (BOM)
- Lists all components like pipes, elbows, tees, reducers, valves, gaskets, flanges, etc., required for that isometric.
🔹 4. Insulation Type
- Specifies whether the line requires thermal insulation, acoustic insulation, or painting, and the type/material.
🔹 5. NDT (Non-Destructive Testing) Requirements
- Mentions the type and extent of NDT (e.g., 100% Radiography, PT, UT) for weld joints.
🔹 6. Revision Status
- Tracks drawing revisions with version numbers, dates, and changes made.
🔹 7. Material Classification
- Identifies the material class (e.g., CS, SS, Alloy) as per project specification.
🔹 8. Design, Operating & Test Pressure/Temperature
- Specifies the design conditions to select suitable pipe materials and test limits.
🔹 9. Paint or Coating System
- Provides paint specification or coating system (e.g., epoxy, galvanized) for corrosion protection.
🔹 10. P&ID Reference
- Links the isometric drawing to the parent P&ID (Piping & Instrumentation Diagram).
🔹 11. Slope / Drain Details
- Indicates required slope direction and gradient for lines like drains, vents, and sloped pipelines.
🔹 12. Service Details
- Tells what fluid or gas the line carries (e.g., steam, water, oil, nitrogen).
🔹 13. Flow Direction
- Shows arrow marks to indicate the direction of fluid flow in the line.
🔹 14. Pipe Support Details
- Highlights locations and types of supports, such as hangers, guides, or shoes.
🔹 15. General Notes / Special Instructions
- Additional instructions like welding sequence, spool splitting, or vendor notes.
🔍 In simple words:
An isometric drawing is the blueprint that tells you what to build, how to build, and with what materials—making it essential for fabricators, inspectors, and engineers on site.
Q- What types of codes and standards do you use as a Piping Inspector?
Answer:
As a Piping Inspector, your work must comply with recognized international codes and standards to ensure safety, quality, and technical correctness in piping design, fabrication, installation, testing, and inspection.
Below are the main international codes and standards commonly used in the piping industry:
📘 ASME Codes (American Society of Mechanical Engineers):
🔹 ASME B31.3 – Process Piping
- The most widely used code in refineries, chemical, petrochemical, and gas processing plants.
- Covers design, materials, fabrication, inspection, testing, and safety of process piping systems.
🔹 ASME B31.1 – Power Piping
- Used in power plants and boiler systems, handling high-pressure steam and water.
🔹 ASME B31.5 – Refrigeration Piping and Heat Transfer Components
- Applies to industrial and commercial refrigeration systems including piping, components, and safety requirements.
🔹 ASME B31.9 – Building Services Piping
- Covers low-pressure piping systems for heating, air conditioning, plumbing, and ventilation inside buildings.
🔹 ASME Section IX – Welding Qualification
- Governs the qualification of welding procedures (WPS, PQR) and welder performance (WPQ).
- Essential for ensuring weld quality and compliance with construction codes.
🔹 ASME Section V – Nondestructive Examination (NDE)
- Provides requirements and guidelines for NDT methods like Radiographic Testing (RT), Ultrasonic Testing (UT), Magnetic Particle Testing (MT), and Dye Penetrant Testing (PT).
🔹 ASME Section II – Materials
- Covers specifications for materials including mechanical properties, chemical composition, and testing standards.
🌍 Other International Standards and Guidelines:
🔹 API (American Petroleum Institute)
- API 570 – Piping Inspection Code (used for in-service inspection)
- API 574 – Inspection Practices for Piping System Components
- API 5L – Specification for Line Pipe
- API 6D – Specification for Valves
🔹 ASTM (American Society for Testing and Materials)
- Provides standards for materials, testing, and mechanical properties (e.g., ASTM A106, ASTM A105, ASTM A312)
🔹 ISO Standards (International Organization for Standardization)
- ISO 9001 – Quality Management Systems
- ISO 14692 – For GRP piping systems
🔹 AWS (American Welding Society)
- AWS D1.1 – Structural Welding Code for Steel
- Commonly referred to for welding practices and symbols
🛠️ Why These Codes Matter for a Piping Inspector:
- Ensure compliance with international safety and quality standards
- Enable proper inspection, testing, and documentation
- Maintain uniformity across global projects
- Prevent failures by adhering to recognized engineering practices
🔍 In simple words:
A piping inspector must follow globally recognized codes like ASME, API, ASTM, AWS, and ISO to ensure that all piping work is technically correct, safe, and of high quality.
Q- What are the types of valves used in piping systems?
Answer:
Valves are essential components in a piping system. They are used to start, stop, control, or regulate the flow of fluids (liquids or gases). Valves are classified based on their design, function, and application.
🔹 Common Types of Valves (Based on Design):
1. Gate Valve
- Used for on/off service (full open or full close).
- Not suitable for throttling.
- Operates by lifting a gate out of the fluid path.
- Provides minimal pressure drop when fully open.
✅ Use: Isolation of fluid in pipelines.
2. Globe Valve
- Designed for flow regulation.
- Offers better control than gate valves.
- Has higher pressure drop due to flow direction change.
✅ Use: Throttling and flow control applications.
3. Butterfly Valve
- Rotating disc controls the flow.
- Compact, lightweight, and suitable for large pipes.
- Quick to open/close.
✅ Use: Low-pressure applications, water lines, ventilation.
4. Check Valve (Non-return Valve)
- Allows flow in one direction only.
- Prevents backflow in the system.
- No external control needed.
✅ Use: Pump discharge, compressor lines.
5. Needle Valve
- Precise control of flow using a slender, needle-like plunger.
- Best for fine regulation of flow in small pipelines.
✅ Use: Instrumentation and lab systems.
6. Control Valve
- Operated automatically to regulate pressure, temperature, or flow.
- Often integrated with actuators and sensors.
✅ Use: Process control systems in industries.
7. Knife Gate Valve
- Has a sharp-edged blade to cut through thick or viscous fluids.
- Good for slurry, wastewater, or pulp applications.
✅ Use: Mining, chemical, and waste treatment plants.
🔸 Classification Based on Function:
| Function Type | Explanation | Examples |
|---|---|---|
| Isolation Valve | Used to completely stop the flow when required | Gate, Ball, Butterfly |
| Regulation Valve | Used to control or throttle the flow rate | Globe, Needle, Control |
| Non-Return Valve | Prevents backflow in a pipeline | Check Valve |
| Special Purpose Valve | Designed for specific fluids or conditions | Knife Gate, Pressure Relief |
📌 Quick Summary Table:
| Valve Type | Main Purpose | Manual / Automatic | Used For |
|---|---|---|---|
| Gate Valve | Isolation (On/Off) | Manual | Oil, gas, water, steam lines |
| Globe Valve | Flow regulation | Manual | Fuel, water, chemical processes |
| Butterfly Valve | Quick isolation | Manual / Auto | HVAC, water treatment, large pipelines |
| Check Valve | Backflow prevention | Automatic | Pumps, compressors |
| Needle Valve | Precise flow control | Manual | Instrumentation systems |
| Control Valve | Automated regulation | Automatic | Process control loops |
| Knife Gate Valve | Handling slurries | Manual / Pneumatic | Pulp, mining, wastewater |
🔍 In simple words:
Valves are chosen based on what they need to do — stop flow, control flow, or prevent reverse flow — and each valve has its own design suited to specific conditions.
Q- What are the main things you will check before bolt torqueing?
Answer:
Before performing bolt torquing on a flange joint or any mechanical connection, a piping inspector or technician must ensure certain parameters are checked and verified to achieve the desired tightness, leak-free sealing, and safety compliance.
Here are the main things to check before bolt torquing:
🔹 1. Correct Bolt Size and Material
- Verify the bolt size, length, diameter, and grade as per the flange specification.
- Ensure compatibility with flange pressure rating and design standard (e.g., ASME B16.5).
🔹 2. Calibration Status of Torque Wrench
- Ensure the torque wrench (manual or hydraulic) is calibrated and within valid certification date.
- Calibration certificates must be available and traceable.
🔹 3. Torque Tool Type – Manual or Hydraulic
- Choose the appropriate tool based on bolt size and torque requirement:
- Manual torque wrench for small to medium bolts.
- Hydraulic torque tools for large-diameter, high-torque flanges.
🔹 4. Lubricant Application
- Verify that approved thread lubricant (anti-seize compound) is applied on bolt threads and under the nut face.
- This reduces friction and ensures accurate torque transfer.
🔹 5. Friction Factor Consideration
- Consider the friction factor of the lubricant when calculating torque.
- Friction affects the actual preload applied to the bolts, which influences gasket sealing.
🔹 6. Torque Value Confirmation
- Confirm the torque value as per flange standard or engineering instruction (e.g., ASME PCC-1 guidelines).
- Follow the torque-tightening sequence (typically a star pattern) and staging method (in multiple passes).
🔹 7. Cleanliness of Flange Faces and Bolts
- Ensure that flange surfaces, threads, and gasket seating areas are clean and free from dirt, rust, or debris.
- Contamination can affect sealing and bolt load accuracy.
🔹 8. Gasket Type and Position
- Confirm the correct gasket is installed and properly centered between the flange faces.
🔹 9. Compliance with Standards
- Follow applicable ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly).
- Also refer to standards like ASME B16.5, ASME B16.47, and company-specific procedures if required.
🔍 In simple words:
Before torqueing, check the tools, bolts, lubricant, gasket, torque values, and cleanliness to ensure a leak-proof and safe flange joint.
Q- Hydrostatic Test Punch List Items Prior to Commencing Hydrotest at Site.
Before conducting a hydrostatic pressure test on any piping system, it is critical to ensure that all preparatory and safety conditions are fully met. Below is a comprehensive checklist of items that must be verified and completed before starting the test:
🔧 Pre-Hydrotest Punch List Items
- All hot work shall be completed
➤ All welding, cutting, or grinding must be fully finished before testing to ensure no structural changes during or after testing. - Strainers shall be removed
➤ Temporary strainers, filters, and internal components susceptible to damage must be removed prior to hydrotest. - All NDT (Non-Destructive Testing) & DT (Destructive Testing) shall be completed
➤ All welds must be inspected and accepted as per project specifications and applicable codes (e.g., ASME B31.3). - PWHT (Post Weld Heat Treatment) shall be completed
➤ All joints requiring heat treatment must have it completed and documented before pressure testing. - Adequate pipe supports and attachments shall be installed
➤ Both permanent and temporary supports must be in place to maintain pipe alignment and prevent sagging or stress. - Coating on weld joints shall be removed
➤ All painted or coated areas covering the welds must be cleaned to allow visual leak detection during the test. - Calibration of all testing equipment shall be verified
➤ Pressure gauges, torque wrenches, and other tools must be calibrated and have valid certification.
➤ Test blind flanges must have material test certificates (MTCs). - Test fluid certificates shall be reviewed and accepted
➤ The hydrotest medium (typically clean water) should be non-corrosive and free from contaminants, especially for stainless steel systems. - Sensitive internal components shall not be installed
➤ Devices such as orifice plates, flow nozzles, sight glasses, and similar instruments that could interfere with filling, venting, or draining must be removed or not yet installed. - All flange, threaded, and welded joints shall be left exposed
➤ No insulation, wrapping, or obstruction is allowed. Visual inspection of all joints for leaks is mandatory during the strength test. - Flange joints must be inspected, and gasket material verified and properly torqued
➤ Ensure correct gasket installation and torque values are applied in accordance with torque charts or specifications. - Drains shall be provided at all low points of the piping system
➤ Proper drainage points ensure complete removal of water after the test. - Vents and drain valves (temporary or permanent) must conform to the piping class/rating
➤ Ensures compatibility and safety during pressurization and depressurization. - Pipe supports are installed as per design
➤ Temporary supports may be added if needed to prevent pipe displacement during testing. - Expansion joints, spring hangers, and supports must be temporarily restrained
➤ Prevents movement or damage during test pressure application. - Arc strikes, gouges, or other poor workmanship signs must be removed and inspected
➤ Surface defects must be ground smooth and re-inspected using MT (Magnetic Particle Testing) or PT (Penetrant Testing). - Drains provided immediately above vertical check valves
➤ Prevents trapped air or fluid that could affect test accuracy or valve performance. - All threaded joints up to the first block valve in hydrocarbon systems are seal welded
➤ Ensures no leakage from threaded connections. Thread engagement must also be verified. - Pressure testing manifold is pre-tested
➤ The manifold should be pressure tested separately to at least 1.2 times the intended test pressure, or not less than the discharge pressure of the test pump. - Line compliance with isometric drawings is confirmed:
i. Material grade/schedule matches Bill of Materials
ii. Flange and fittings ratings are correct
iii. Construction tolerances are met as per project standard
📌 Conclusion:
Performing the above checks ensures:
- Test safety
- Leak-free performance
- Code and project compliance
- Long-term piping reliability
Bonus Items (Recommended to check):
- ✅ All gaskets and torques verified and flange joints properly aligned.
- ✅ Drains at low points and vents at high points are installed and accessible.
- ✅ Temporary supports or restraints installed on expansion joints or spring supports.
- ✅ Arc strikes and weld defects are ground and inspected (MT/PT).
- ✅ Ensure line complies with Isometric drawing, material class, and construction tolerances.
Q- Which type of documents/reports are attached in a hydrostatic test package?
Answer:
A Hydrostatic Test Package (HTP) is a collection of documents that verifies a piping system has been tested according to project specifications, international codes (e.g., ASME B31.3), and client requirements. These documents serve as official records and ensure compliance, traceability, and quality assurance.
📁 Documents/Reports Included in a Hydrostatic Test Package:
- Hydrotest Procedure
➤ Approved method statement or procedure describing how the test is conducted. - Hydrotest Clearance/Permit
➤ Approved permit from QA/QC, operations, or safety department authorizing the test. - Approved P&ID and Isometric Drawings
➤ Marked-up or test-approved drawings showing line identification, test boundaries, and any modifications. - Line Check Reports / Punch List Clearance
➤ Verified documentation showing that the line has been physically inspected and all punch items are cleared. - Test Pressure Calculation Sheet
➤ Document showing the design pressure, test pressure, test duration, and applicable code reference (e.g., ASME B31.3 formula). - Calibration Certificates of Pressure Gauges and Recorders
➤ Valid certificates for all measuring instruments used in the test. - Flange Management Checklist / Bolt Torque Records
➤ Records showing all flanged connections were assembled, torqued, and inspected properly. - Material Test Certificates (MTCs) for Test Blinds and Components
➤ Certification for test blinds, temporary fittings, or materials used during testing. - Test Fluid Certificate (Water Quality Report)
➤ Report verifying that the test fluid used (e.g., water) is clean and suitable for the tested material (non-corrosive). - Test Manifold Pressure Test Report
➤ Documentation confirming that the test manifold was pre-tested to required pressure. - Pressure Test Log Sheet / Chart Recorder Graph (if used)
➤ Actual test data showing:
- Start and end time
- Test pressure
- Ambient temperature
- Any drop in pressure
- Signature of inspectors and witnessing authorities
- Visual Inspection Report Post-Hydrotest
➤ Confirmation that all joints were visually inspected for leaks and condition after testing. - Photographic Evidence (if applicable)
➤ Photos of gauge readings, joint conditions, or any special test setups. - Witness / Approval Signatures
➤ Sign-off by contractor, client, QA/QC, and third-party (if required) confirming successful test. - Test Acceptance Certificate
➤ Final document confirming that the system passed the hydrostatic test and is accepted for further process (e.g., insulation or commissioning).
📌 Note:
- All documents must be properly numbered, signed, dated, and stamped as per the project’s document control system.
- The Hydro Test Package becomes part of the Mechanical Completion Dossier or Turnover Package to the client.