The following section will list some interview questions asked in the different interviews for a Pipeline Engineer Position. Readers are requested to provide the answers in the comment section which I will add in the main section in due course.
Explain the basis of pipeline hydraulics and how will differentiate the gas and crude oil pipeline that is which method will perform to do the calculation.
What are all the softwares available in the market to perform pipeline hydraulics and how will you check the input and output?
What are the criteria for route selection of gas and crude oil pipelines?
For the sloped pipeline, how to fill the water during the hydrostatic test and why?
Explain the hydrostatic test pressure with respect to ASME B 31.8/31.4. How do they arrive the 90% of SMYS and what is the basis?
Explain about one pipeline project lifecycle, starting from concept, FEED, Detail Design, and construction (Sequence).
What is the difference between PSL-1 and PSL-2, what are all the tests involved during manufacturing?
What is the procedure/sequence of linepipe manufacturing?
What % of line pipe is radiographically tested during manufacturing?
Spiral welding can be used in oil and gas, if No, why?
Wadi crossing types and construction methods.
Isolation joints internal and external coating requirements and temperature ranges.
Draw and explain the pig launcher and receiver sequence.
What are the proximity distances and no. of buildings according to the location class?
Where are Isolation joints to be installed and why? In IJ above 50 bar, what is the precaution?
Draw the pig trap and explain pigging the procedure.
Explain about CMA fittings and location, why?
Compare a BVS requirement with EIA.
What are the differences between restrained and un-restrained pipelines?
What are the criteria for expansion loops for un-restrained pipelines? During A/G pipeline design how expansion loops will be fixed?
What are the types of supports used for pig traps and why?
Tell about allowable displacement values and if exceed the limit what are the other considerations to be taken care of to have a flexible pipeline system during design.
What is Carbon Equivalent (CE) for line pipe and split tees? If two different CE pipes are needed to weld, which CE value has to be considered for qualification?
DWTT and CVN tests – Explain.
Explain the minimum branch sizes on pipelines.
Golden weld joints – explain what tests need to be performed for golden joints.
External coating types and temperature range.
Velocity accepted during the design for liquids and gas?
During End closure design what are the safety devices we have to consider?
During the design of pipeline design life, what are the factors to be considered?
PWHT requirement on the pipelines.
How you will protect your pipeline and flowline: explain from the well to manifold and manifold to the station.
Explain the pipeline design of the high temperature and pressure.
What are the major differences between ASME B31.4 and ASME B31.8?
A pipeline carries a fluid having a temperature of 250 Degrees C. Which ASME code will be used to design that pipeline?
A reciprocating compressor is a kind of positive displacement compressor that compresses and delivers air or gas at high pressure using a reciprocating component, such as a piston or plunger. The piston of the reciprocating compressor moves forward and backward, compressing the gas or air. For this reason, another name for it is a piston compressor. The gas or air in this compressor is drawn into the chamber and compressed by a reciprocating piston. The working fluid volume is moved by this piston to function. Applications requiring both high gas pressure and low flow rate are often served by reciprocating air compressors. Fig. 1 below shows the working of a reciprocating compressor.
Fig. 1: Working of a Reciprocating Compressor
Codes and Standards for Reciprocating Compressor:
Various codes and standards govern the design and manufacture of reciprocating compressors:
API Standards: API-11P (Packaged Reciprocating Compressors) and API-618 (Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services)
ISO Standards: ISO-13707 and ISO-13631
Shell DEP: DEP 31.29.40.31
API RP 688 for Pulsation and Vibration Control
Reciprocating Compressor Sizing:
Reciprocal compressor sizing has been a task for many decades. Engineers, packagers, and end users can benefit from the robust sizing software offered by the majority of reciprocating compressor OEMs nowadays. However, these sizing tools might produce inappropriate and deceptive hardware suggestions if not used carefully and with attention to detail.
A typical compressor sizing methodology proceeds as follows:
Inlet and discharge pressures and a desired flow rate are specified by the Client.
A gas analysis or equivalent is specified by the Client.
Steps for selecting the proper compressor:
Calculate the compression ratio.
Choose the number of stages of the compressor.
Calculate Estimated BHP.
Calculate estimated Discharge Pressure.
Calculate the discharge temperature.
Determine the suction volumetric efficiency.
Calculate the required piston displacement.
Determine the Velocity of Valves
Determine the Gas rod loads.
Selecting of Reciprocating Compressor cylinder and Frame by using the OEM Design Data
OEMs typically carry out steps 1 through 10 using sophisticated software, however hand calculations are frequently sufficient.
Step 1: Calculate the Compression Ratio (CR):
A single-stage compressor has only a single R-value. Whereas a typical two-stage compressor has three R values.
CR (or) R = total compression ratio for the compressor
R1 = compression ratio for the first stage
R2 = compression ratio for the second stage
R = Pd/Ps, R1 = Pi/Ps, R2 = Pd/Pi
Here,
Ps=Suction pressure,
Pd=Discharge pressure,
Pi=Interstage pressure – the pressure between the 1st and 2nd stages of the compressor.
Step 2: Calculate / Choose no. of stages of the compressor:
The number of stages can also be determined using the thumb rule, which is shown in Fig. 2, however, it depends on the OEMs.
Fig. 2: R-value vs Number of Stages
Step 3: Calculate Estimated Power (BHP):
Where, Ƹad = Volumetric adiabatic Efficiency (From Figure 3); k = specific heat of the gas. Compression Ratio R= (P2/P1); Flow Rate (MMSCFD)
It is crucial to estimate the number of stages, power required, and interstage pressures. Every OEM has a set number of frames and a family of standard cylinders that are predesigned to fit those frames. As a result, the number of possible frame/cylinder combinations is limited. The best option any specific OEM can offer is at least one of the potential combinations.
Step 5: Calculate the discharge temperature (oR)
The life of the valves and piston rings is directly impacted by the compressor’s discharge temperature. The discharge temperature of an air-cooled single-stage compressor can be determined using the following formula:
Ts Suction temperature °R (°K)
Ps Suction pressure PSIA (Bar-a)
Pd Discharge pressure PSIA (Bar-a)
R Compression Ratio (Pd/Ps)
n specific heat ratio of the gas.
Step 6: Determine the suction volumetric efficiency
Volumetric efficiency includes many factors that help explain the differences between ideal gas behavior and real gas behavior. In general, volumetric efficiency depends upon compression ratio, cylinder clearances, gas compressibility values, and the ratio of specific heats (k or N value) (Z1, Z2, and k values are specified in Gas properties). CL might be 15% (CL = 0.15) for normal cylinders and 65% (CL = 0.65) for pipeline cylinders.
*Where L is taken from Figure 4.
Fig. 4: Ratio of Compression vs Loss Correction
Step 7: Calculate the required piston displacement
Piston displacement is the actual volume displaced by the piston as it travels the length of its stroke from Position 1, bottom dead center, to Position 3, top dead center. Piston displacement is normally expressed as the volume displaced per minute or cubic feet per minute.
Step 8: Determine the Velocity for Valves
Compressor valves are the most critical part of a reciprocating compressor. Generally, they require the most maintenance of any part. They are sensitive both to liquids and solids in the gas stream, causing plate and spring damage and breakage. When the valve lifts, it can strike the guard and rebound to the seat several times in one stroke. This is called valve flutter and leads to breakage of valve plates.
Where,
V = average velocity in feet/minute.
D = cylinder displacement in cubic feet/minute.
A = total inlet valve area per cylinder, calculated by valve lift times valve opening periphery, times the number of suction valves per cylinder, in square inches.
Step 9: Determine the Gas rod loads
Gas rod loads are calculated based on internal cylinder pressures. The equations below are based on pressures in gauge units. If absolute units are applied, then additional terms for Patm being applied on the piston rod diameter must be included.
Thumb Rules for good Compressor sizing:
Rod loads < 100%
Rod reversal Degree (Xhd pin degree / % Rvrsl Lbf) > 30% & Force > 25%.
Step 10: Selecting of Reciprocating Compressor cylinder and Frame by using the OEM Design Data
Once the above steps are calculated, use the calculated Volumetric Efficiency, Maximum HP, Displacement, Discharge Temperature, and Gas Rod Loads and check with respective OEMs design data to determine the number of Strokes and speed (RPM). Using these Strokes and speed calculate the Cylinder Area as per below.
By this, the Cylinder area is determined which helps in finding out the right Cylinder bore and Cylinder model. It also helps us in deciding the number of Cylinders used in the multistage compressor. Attached below is the Performance chart for reference where it satisfies all the user criteria and with cost cost-effective selection of the reciprocating compressor and its frames and cylinder Models.
Fig. 5: A Typical OEM software compressor Sizing outputs for Reference
Centrifugal Compressors: Applications, Types, Functions, Parts, and Design Guidelines
Compressors are intended to compress a substance in a gaseous state. Process compressors are used to compress a wide range of gases over a wide range of conditions. A Centrifugal compressor is a dynamic turbomachinery that increases the pressure of a gas by adding kinetic energy through an impeller. The famous French genius, Professor Auguste Rateau, invented the centrifugal compressor in the late 19th century. Smooth operation, large tolerance of process fluctuations, and higher reliability are the factors that Centrifugal compressors find extensive use in chemical and petrochemical industries. They are also used in small gas turbines.
The following diagram shows a chart for basic compressor types.
Fig. 1: Compressor types
Centrifugal Compressors
A Centrifugal compressor is a “dynamic” machine. It has a continuous flow of fluid that receives energy from an integral shaft impeller. The Energy transformed into pressure – partly across the impellers and partly in the stator section called diffusers. The main characteristics of a centrifugal compressor are
Dynamic Compressor: Achieves a pressure rise by adding Kinetic Energy /Velocity to fluid
Narrow operating range: Operates close to the design point due to its characteristics.
Capacity control is simple using either a Suction Throttle or Speed Control.
Can be used for pushing large volumes of gas (large volumetric capacity)
Why Centrifugal?
There are various benefits of being it centrifugal like
It is a mature technology
Suitable for large capacities
Power Range from 0.4 to 40 MW
Small footprint
High Availability (99%)
Less Maintenance
Parts of a centrifugal Compressor
Refer to Fig. 2 below that shows the Cross section & parts of a typical centrifugal compressor:
A. Outer casing
B. Stator parts called ‘Diaphragm bundle’
C. Rotor
D. Impellers
E. Balance drum
F. Thrust collar
G. Hub
H. Journal Bearing
I. Thrust Bearing
J. Labyrinth Seals
K. Oil film end seals
Fig. 2: Cross section of a typical Centrifugal Compressor
How does a Centrifugal Compressor work?
Through the centrifugal compressor suction, the gas enters the rotating impeller. While passing through the blades, the gas is pushed by centrifugal force toward the impeller center. The impeller provides kinetic energy to the gas and the velocity increases. This kinetic energy is then converted into potential energy in the form of pressure increase. Again, while passing through a diffuser, the gas is compressed further. So, both the diffuser and impeller help in gas compression. On average, 65% of compression takes place in the rotor and 35% in the diffuser. For multistage centrifugal compressors, each stage increases the pressure which results in final higher pressure.
Types of Centrifugal Compressors
Depending on the number of impellers and casing design, centrifugal compressors are classified into three groups as follows:
Integral Gear Type
Single Stage
Multistage
Horizontal Split Casings
Single Stage (Double Suction)
Multistage
Barrel Type Compressors
Pipeline
Multistage
Compressors with Horizontal Split casings (Fig. 3):-
Consists of half casings joined along the horizontal centerline, Employed for operating pressure below 60 bar.
Fig. 3: Centrifugal Compressor with Horizontal Split Casing
Compressors with Vertical Split casing/Barrel Type (Fig. 4):-
Vertical split casings are formed by cylinders closed by two end covers; hence ‘barrel type’ is used to refer to these compressors, Employed for high-pressure services up to 685 bar.
Fig. 4: Centrifugal Compressor with Vertical Split Casing
The Horizontal split casings & barrel compressors are further identified based on process stages, i.e.
Multistage compressors with one compression stage
Multistage compressors with two compression stages (Two compression stages set in the same machine/barrel casing. Between the two stages cooling of the fluid is performed in order to increase the efficiency of compression)
Basic Terminologies of Centrifugal Compressor
Surge: A phenomenon of instability that takes place at low flow which involves the entire system including not only the compressor but also the group of components traversed by the fluid upstream & downstream of it. Surge is characterized by intense and rapid flow and pressure fluctuation throughout the system and is generally associated with a stall involving one or more compressor stages. This phenomenon is generally accompanied by strong noise and violent vibrations which can severely damage the machine involved
Stall: Stall in turbomachinery describes as a situation in which due to low flow values, the stage pressure ratio or head does not vary in a stable manner with the flow rate.
Surge prevention: Surge prevention is effected through experimental tests in which pressure pulsation at a low flow rate is measured on individual stages. On this basis, it is possible to identify the flow values at which the stable operation of the stage is guaranteed.
Centrifugal Compressor Design Guidelines
1. Design Parameters: Centrifugal compressors in Process industries are designed following API 617. The following parameters are required to properly design a centrifugal compressor are:
Type of gas
Temperature, pressure, molecular weight, and corrosion properties of the gas.
Possible gas fluctuations.
2. Flow Rates: A flow rate of approx. 180 m3/h is considered a minimum for any impeller. With a decrease in flow rate towards this limit, the efficiency of the centrifugal compressor falls.
3. Application Pressure Range: With proper seals, there is no limitation on lower pressures. However, the upper limit of operating pressure is limited by the use of thicker components and the number of stages in a single casing (generally limited to 8). For horizontally split designs, discharge pressures are generally up to 100 bar. For radially split (barrel) designs, discharge pressures can be up to 800 bar.
High suction pressures lead to difficulties in sealing and the majority of applications have suction pressures of less than 200 bar.
4. Application Temperature Range: The lower temperature can be as low as -75⁰C with due consideration of materials that provide ductility & sufficient brittle strength. Sealing materials should be compatible.
Commonly encountered higher temperature is 180-190⁰C. For higher temperatures up to 230⁰C cool buffer gas may be injected.
5. Number of Stages: The compression ratio or head defines the number of stages or impellers. A general rule is to have only nine impellers per casing in a single-section centrifugal & eight impellers per casing for a two-section centrifugal. In the special case of a compressor having a side stream entry, the maximum no of impellers should be seven per casing.
6. Rotating Speed: Higher rotative speeds give improved performance in terms of work per stage. A general rule of thumb is that impeller tip speed should normally range between 650 and 900 ft/sec (198 and 274 m/s) for fully enclosed impeller designs. For open impeller design, the maximum tip speed limit is higher due to the reduced centrifugal forces generated with the absence of the mass of the cover.
7. Compressor Efficiencies: In industrial applications of centrifugal compressors, two types of compressor efficiencies are used. They are Isentropic Efficiency and Polytropic Efficiency. Isentropic efficiency is given by isentropic compression work / actual compression work.
For centrifugal compressors, Polytropic efficiency is commonly used in work or power calculations. The polytropic process follows a path such that the polytropic exponent is constant during the process, PVn=constant; where: n= polytropic exponent. The polytropic exponent (n) and the isentropic exponent (k) (for an ideal frictionless adiabatic process) are related as follows:
The Polytropic efficiency can also be calculated based on the inlet volume flow since the polytropic efficiency is nearly proportional to the logarithm of the inlet gas volume flow rate.
Capacity Control
Capacity Control is used for the following:
Process flow control
To optimize fuel/power efficiency
Pressure regulation
Capacity can be changed in several ways; below are some of them:
Speed Regulation
Control of Supply gas to the machine
Bypassing the discharge flow back to the suction side of the machine
Type of Compressor Drives
Following are the various types of Compressor drives:
The type of compressor & method of lubrication used will decide the type of sealing Technology. Sealing System can be divided into two classes based on the type of lubrication:
Contacting Sealing System
Liquid Lubricated
Gas Lubricated
Non – Contacting Sealing System
Liquid Lubricated
Gas Lubricated
The following are the utilities required for the Compressor:
External Fuel gas for seal gas system
Instrument Air for the Instruments/Control system/Seal gas system
Centrifugal Compressor vs Axial compressor
The main differences between a centrifugal compressor and an axial compressor are provided in the table below:
Centrifugal Compressor
Axial compressor
In a centrifugal compressor, Gas enters the impeller axially and is discharged radially.
In an axial compressor, The gas enters and exits axially without directional change.
Easier to design and manufacture
Difficult to design and manufacture
The volume of gas flow is less
Can handle more gas flow.
Less efficient
More efficient
Can create more differential pressure in a single stage
Single-stage compression is not effective.
Table: Centrifugal Compressor vs Axial Compressor
Centrifugal Compressor vs Reciprocating Compressor
Piping systems are the veins of industrial plants, carrying fluids and gases critical for various processes. Ensuring the reliability and safety of these piping systems is paramount, and this is where Advanced Pipe Stress Analysis comes into play. Advanced Pipe Stress Analysis goes beyond basic analysis, offering a comprehensive understanding of how pipes behave under various conditions.
Pipe Stress Analysis is a critical aspect of piping design that evaluates the effects of loads, pressures, and thermal gradients on a piping system. Basic Pipe Stress Analysis typically considers factors like pressure, temperature, and weight to ensure the system’s integrity. However, as systems become more complex and industries demand higher efficiency, Advanced Pipe Stress Analysis becomes essential.
Various sophisticated software tools are essential for Advanced Pipe Stress Analysis. One such powerhouse in the field is Caesar II. Developed by Hexagon PPM, Caesar II is a widely used software application that plays a pivotal role in ensuring the integrity and reliability of piping systems. Caesar II allows engineers and designers to model, analyze, and optimize piping systems. Known for its robust capabilities, the software enables a comprehensive evaluation of various factors influencing pipe behavior, providing a detailed understanding of stress, deformation, and stability under different operating conditions. Throughout the course, the explanations and case studies are provided using Caesar II software.
The complete online pipe stress analysis course is divided into several modules. Each module will explain some aspects of Pipe Stress Analysis that are required for every pipe stress engineer. New modules will be added as and when prepared. You can enroll in the module that you require.
Module 1: Basics of Pipe Stress Analysis (Duration: 5 hours)
Pipeline Thickness Calculation Steps for Restrained and Unrestrained Pipelines
Example of Pipeline Thickness Calculation for Aboveground Pipelines
Buried Pipeline Thickness Calculation Case Study
Additional Checks to satisfy pipeline thickness calculations
As mentioned earlier, new modules will be added frequently. So, keep visiting this post. Also, you can request any specific module by mentioning it in the comment section.
Is Pipe Stress Analysis Required for Cold Water Piping Systems from Pump Stations?
Is Pipe Stress Analysis Required for Cold Water Piping Systems from Pump Stations? This is perhaps one of the most frequently asked questions in the water piping industry. Engineers often argue over this question which results in a dual answer. Some engineers say stress analysis is not required and others say it is required. In this article, we will explore the answer to the above question.
The answer to the above question is not straightforward. In general, as for water piping systems with pump stations, the difference between the maximum working temperature and installed temperature (generally 10 to 20 Degrees) is less, hence it is believed that pipe stress analysis of such water piping systems is not required. This could be valid up to a certain point if good engineering judgments are followed and the piping system is provided with sufficient flexibility.
But before we can conclude, a high level of assessment must be conducted to understand if pipe stress analysis is required. The parameters that substantiate the need for pipe stress analysis are:
How an increase in pipe temperature affects the system:
Even though it is believed that the water piping system will be near to installed temperature. Still, there could be variation due to the following reasons:
Seasonal variation of temperature from winter to summer.
Empty pipe exposed to sunlight.
Full pipe exposed to sunlight.
Temperature variation between day and night.
How external forces and displacements affect the water piping and Pump system:
Forces and displacements due to seismic, wind, and structural settlements may impose unacceptable levels of stress on the system. These stresses can not be estimated without proper pipe stress analysis.
Limitation of Pump Nozzle Loadings:
It’s difficult to estimate the nozzle loads without performing pipe stress analysis.
Support optimization:
Cold water piping systems usually have very large sizes along with large valves that result in huge structural loading. Without proper stress analysis, those loads can be overestimated and support optimization may not be possible.
Design of Expansion Bellows or Expansion Joints:
The use of rubber bellows or steel expansion joints at pump stations for water piping systems is quite common. In general pump stations are routed quite straight without much flexibility. So, these expansion joints are used to absorb thermal expansion which in turn reduces pump nozzle loads.
However, there is a concern as the subject of expansion joints is one of the most misunderstood components in the piping industry. In the usual case, simple untied bellows are used which is simply a flexible element between two flanges. It is true that they easily absorb the thermal expansion by compressing the bellow elements in all axial, lateral, angular, and torsional directions. However, a pressure thrust force is generated in untied expansion joints which must be calculated and considered in pipe stress analysis to get the actual effect. This pressure thrust force will be transferred to the pumps. In some situations, the pressure thrust force, itself, will be more than the allowable pump nozzle loads.
Another option is to use a tied expansion bellows. However, even though the tie rods will take care of the pressure thrust load, they will not compress to absorb axial movement and the thermal effect will be transferred to the nozzles. So, their position has to be such that the thermal movement is lateral.
A common misconception is to use tied bellows to a pump line with a gap in the tie nut and believe that the tie rods will take care of the pressure thrust force and the gap between the tie rod nuts will help in absorbing the thermal force by compressing. But as soon as any thermal expansion occurs, the tension in the tie-rods reduces and the pressure thrust load is transferred to the nozzle. So, this has to be carefully considered.
Typical Example of a Pump Station Cold Water Piping System
Fig. 1 below shows a typical example of a water piping system pump station.
Fig. 1: Cold Water Piping from Pump Station
From the image, you can easily understand that the configuration does not have sufficient flexibility, and nozzle loads may increase the allowable.
We all know that a hydrostatic test is performed in all piping systems to ensure the integrity of all the joints. It is a code requirement before the commissioning of the piping/pipeline system. However, in certain situations, hydrostatic testing may not be technically feasible or may be hugely cost-intensive. For example, When a new piping component is connected to an already existing pipe. The situation may not always be favorable for hydro tests. In such a situation, the golden joint comes as a savior to construction professionals. In this article, we will learn the meaning and applications of golden joints in piping.
What is a Golden Joint?
Golden Joint is a pipe/pipeline joining procedure where hydro testing is not performed after the joining. Extensive NDT methods like radiographic test/ultrasonic testing methods are used to ensure that the joint is defect-free, design is in line with codes and standards, and fit for intended service. A golden joint is also known as a golden weld or closure weld.
Examples of Golden Joints
Some typical examples of golden joints are:
Golden joints in tie-ins from existing pipe parts.
During Hot tapping from running/working/operating pipelines.
When only a little repair work is performed on the system at one or two locations, and hydro-testing of the complete system is difficult, costly, and time-intensive.
Golden Joint Procedure
The requirements of golden weld joints are identified by the construction contractor. Then they mark up the isometric/alignment drawings and get permission from the client. Next following a proper golden joint fabrication method statement, the welding is performed. Next NDE and final inspection clearance is taken and the golden joint is approved. The golded weld or closure weld must be performed by a highly skilled welder.
NDE requirements for Golden Joints
Non-destructive examination or NDE is performed after the PWHT if required by the piping class, thickness, and service limitation. In general, the following NDT tests are performed for golden piping joints.
Radiographic Testing:Radiographic testing can be performed as per the guidelines provided in Article 2 of ASME BPVC Code section V.
Ultrasonic Testing:Ultrasonic testing can be performed as per the guidelines provided in Article 5 of ASME BPVC Code section V.
Magnetic Particle Testing:Magnetic Particle Testing is performed as per the guidelines provided in Article 7 of ASME BPVC Code section V.
Dye Penetration Test:Dye Penetrant testing is performed as per the guidelines provided in Article 6 of ASME BPVC Code section V.
Code requirements for Golden Joints
ASME B31.3 Requirements for Golden Joint
As per clause 345.2.3 (c) of ASME B31.3, The final weld connecting piping systems or components need not be leak tested (golden weld) provided the weld is examined and passes with 100% radiographic examination or 100% ultrasonic examination.
API 570 Requirements for Golden Weld Joints of Piping
As per API 570, when performing a pressure test of a final closure weld that joins a new or replacement section of piping to an existing system is not practical, all of the following four requirements need to be satisfied.
a) The new or replacement piping section is pressure tested and examined by the applicable code governing the design of the piping system, or if not practical, welds are examined with appropriate NDE, as specified by the authorized piping inspector.
b) The closure weld is a weld between any pipe or standard piping component of equal diameter and thickness, axially aligned (not miter cut), and of equivalent materials.
c) Any final closure butt weld shall be of 100 % RT; or angle beam ultrasonic flaw detection may be used, provided the appropriate acceptance criteria have been established.
d) MT or PT shall be performed on the root pass and the completed weld for butt welds and on the completed weld for fillet welds.
The owner/user shall specify industry-qualified UT angle beam examiners for closure welds that have not been pressure tested and for weld repairs identified by the piping engineer or authorized piping inspector.
API RP 14-E Requirements for Golden Joint
API RP 14E recommends that when hydrostatic or pneumatic tests create any adverse effect on the piping or operating fluid, a golden joint can be used.
