In this module, you shall learn about:

ASME Sec. VIII body of knowledge by Part Number.

Introduction

For the purpose of API 510 authorized pressure vessel exam, you only need to know some parts of the ASME VIII, Div. 1 (part ‘’UG’’ for general requirements; Part ‘’UW’’ for welded pressure vessels; part ‘’UCS’’ for carbon steel and low alloy steel pressure vessels.) plus appendices 1-4, 6, 8, 12 & introduction ‘’U’’.

You may note that we have addressed the UW, UG, UCS parts both alphabetically as well as topic wise.

This is because each topic such as post weld heat treatment (PWHT) has cross referenced across ASME VIII parts depending from which angle you are looking at it.

For example, for PWHT of weldments, ‘’UW’’ type comes into picture while for PWHT of base materials, ‘’UCS’’ parts are cross referenced and of course for general requirements, it is ’’UG’’ series.

Hence, the topics (thickness calculation, hydro test, PWHT) are categorized and relevant ASME VIII parts are discussed within those topics in mind.

All these parts are explained in a user friendly format.

If you still may have question, please chat with us and we shall try to explain it in greater detail or provide you with additional material.

Your queries also helps us revise and improve the course material.

What is a Pressure vessel?

PART UW - WELDING

Joint Category: means the location of a joint in a vessel, but not the type of joint. Categories are assigned based on the type and degree of stresses imposed at various locations within a vessel. Joints are categorized as A, B, C or D.

Joint Efficiency: Joint efficiency shows how closely a weld joint approximates the quality of the seamless parent material.

It defines expected efficiency of welded joint strength which basically depends on the percentage of NDE (radiography).

For example, when there is 100% radiography, we can assure ourselves that all the welds are sound and hence we could use the maximum expected strength with a joint efficiency “E” = 1.

As the percentage of radiography decreases, so the certainty that all welds are sound and hence we need to reduce the efficiency of the weld based on this uncertainty. The Joint efficiency plays a vital role in calculating the thickness of the pressure components in Mechanical calculation.

For RT1 and RT2, joint efficiency is 1.0, for RT3 is 0.85 and for RT4 it is 0.70.

Only type 1 and 2 butt joints may be radiographed in order to improve Joint efficiency.

Welded Joints

Weld Types & Symbols

Weld Type is the description of a welded joint. For example, a single-welded butt joint.

Welding defects

UW-2; Service Restrictions

Weld joints are identified by Types (how the weld is NDT tested) and Categories (locations of the weld). If a weld is Category A joint (longitudinal), then it must be type 1 of Table UW-12. If it is Category B joint (circumferential), it must be of either Type 1 or Type 2.

UW-3; Welded Joint Category

The best way to understand and thereby learn joint category is by the use of graphics. Fig. UW-3 of Paragraph UW-3 provides a brief graphical representation.

There shall be several questions regarding weld category which needs you to refer to below figure. You don’t need to memorize the category but should know where to find it (UW-3 , Weld Joint Category, PP. 115).

For joint efficiencies, see ASME VIII UW-12; in page 120 and specifically table UW-12 on page 121.

A quick reference system for specifying joint requirements would be to assign the welds in a vessel by location. For instance, for a vessel in lethal service, the Code requires that butt joints to be of a specific type; based on their physical location in the vessel and that the butt welds to be fully radiographed.

A statement like "All category A joints shall be Type No. (1)." is a concise way of saying the following:

"All longitudinal welds within main shells, communicating chambers, transitions in diameter, or nozzles; any welded joint within a sphere, within a formed head, or within the side plates of a flat sided vessel, circumferential welded joints connecting hemispherical heads to main shells, to transitions in diameter, to nozzles, or to communicating chambers shall be Type No. (1).

UW-3(a)(2) Category B. Circumferential welded joints within the main shell

UW-51 shows the unacceptable indications for Full Radiography. Details of Spot Radiography are covered in UW-52.

Remember acceptance criteria is in ASME VIII, not ASME V which describes the NDT method.

A complete set of radiographs shall be kept on file until the final acceptance by the inspector.

Personnel performing and evaluating radiographs shall be qualified as per SNT-TC- 1A as a guideline for written practices used in their qualification.

Acceptance of radiographs is based on the ability to see the correct penetrameters (IQI) image or the specified hole or wire size as applies.

indication on a radiographic film or radiograph characterized as a crack or incomplete fusion or incomplete penetration is unacceptable.

The acceptable size of elongated indications are based on the materials thickness.

UW-52 Spot Examination of Welded Joints

One spot radiograph for every 50 ft of weld.

Sufficient number of spots shall be radiographed to examine each welder or welding operator in the 50 foot increment.

In case, where welders who weld on opposite sides of the same weld, one shot will serve to examine both.

The inspector chooses the location of the spot radiography. If the inspector approves, the fabricator can then choose the location of the spot radiography. Notice that there is no specific location and the welders should never be able to predict the inspector's choice of location.

Spot radiographs must follow the same rules as full radiographs for techniques.

The minimum length of the spot radiograph must be 6 inches.

Indications described as cracks or zones of incomplete fusion or lack of penetration are unacceptable.
Slag inclusion or cavity evaluation is based on the thickness of the weld excluding any weld reinforcement (cap). The thickness is based on thinner member if two different thickness that have been joined by a butt weld. If a fillet is welded over a full penetration weld, then, its throat must be included in the thickness (t).

Rounded indications are not a factor in the acceptability of welds not required to be fully radiographed.

When a spot radiograph is acceptable; then only the entire weld increment represented is accepted. For example if a longitudinal weld has 65 feet of weld metal only the first 50 feet could be accepted by a single 6 inch spot radiograph. The remaining 15 feet is represented in the next declared 50 feet increment.

If the first spot radiograph ( minimum 6” length) reveals welding that does not comply, then two additional spots ( 2 six inch long minimum) in the same weld increment away from the first spot shall be radiographed (tracers). The choosing of the two spots follow the same rule as the first spot radiograph.

Re-radiography is allowed for the area that was initially rejected but was repaired subsequently.

If either of the two additional radiography fail, there are two options. Cut out the entire increment, re-weld then either apply spot radiography again or apply full radiography and repair all defects that are found by full radiography.

The spot radiography described above is not applied to any specific Category of weld. In a given 50 feet of weld increment there may be Category A, B, C, and D butt welds. The inspector will choose the exact location of the spot radiograph.

UW- 11 Radiographic and Ultrasonic Examination

There are three levels of radiography per Code. Full, Spot and None. The Code requires Full RT in some cases and allows Spot RT or None in others.

UW-11 list the type and category (location) of joints for radiography and ultrasonic examinations. The effect of the degree of radiography is reflected in paragraph UW- 12 with a resulting Joint Efficiency "E". The "E" will be used in the calculating the required thickness or MAWP for shells, heads etc.

ASME VIII; PP. 119: UW-11 specifies when each level of radiography shall be applied.

ASME VIII; PP. 119: UW-11 specifies when each level of radiography shall be applied.

Joint efficiency for butt joins is: 1; 0.85; 0.70 for full, spot and no radiography respectively.

Basic Knowledge

STRESS

Stress as it relates to internal pressure on a vessel is the load divided by area on the vessel's material . Stress is measured in pounds per square inch.

Allowable Stresses and Joint Efficiencies

The Code allows the working stress in a material to be only a fraction of its Ultimate Stress. The term used is "Maximum Allowable Stress" (S).

The limiting of stress in the Code gives a safety factor of about 3.5 to 1.

This means, only 1/3.5 times of ultimate stress of material can be used.

This is under ideal conditions with no known flaws in the vessel's material. This could be a seamless materials properly inspected or a welded material joint fully radiographed.

Most vessels are constructed using welding that introduces flaws into the vessel material. How many and how bad are the flaws? This is answered by the use of non-destructive examination.

If a large enough flaw is present in the base material or the weld, failure can occur at a much lower value of stress.

In the Code formulas, the Stress Allowed (S) must be multiplied by the joint efficiency 'E'. So ‘’SE ‘’always appear in the formulas.

The reason for using ''E'' is to make an adjustment for degree of uncertainty for the welded joint compared to a seamless material.

In the case of full radiography, the welded joint is considered as strong as parent or base material and hence, the joint Efficiency for a Type No. 1 joint can be taken as "1.0".

For a Type No. 2; joint efficiency of 0.90 can be used.

Spot Radiography allows lower joint efficiencies and No Radiography still lower.

In a pressure vessel, the stress in tension is caused by the internal pressure over an area. This force wants to tear the vessel apart and must be resisted by the cross sectional area or the vessel's wall.

The Code limits the amount of stress that can be applied to a vessel's material and this will limit the pressure allowed. If more pressure is applied, you should increase the required thickness accordingly.

The stress in the material caused by the internal pressure is given special concern when there is a welded joint in the vessel's wall. The expected strength of the material is known but how sure we can be if there is a potential flaw existed in a weld or its heat affected zone.

Often the weld joint itself causes a change in the shape of what would otherwise be a uniform cylinder; this will cause what is referred to as a stress raiser. It is safe to say that any weld will cause a stress riser to some extent.

The Code deals with these stress raisers in two ways; 1- by limiting the stress allowed in the material and 2- by assigning joint efficiencies to welded joints and seamless components. The basis for the efficiency of a welded joint is its type and the amount of radiography it has received.

Assigning joint efficiency (E) has a definite effect on the thickness of a vessel or component. The higher the efficiency allowed, the thinner the material is required to be.

ALLOWABLE STRESSES AND JOINT EFFICIENCIES. How Joint Efficiency Affects the Construction of a Vessel?

Let's take an example to better understand it. If a vessel material has an allowable stress of 15,000 pounds per square inch and has a joint that allows an E = 0.85 (Spot RT), the resulting thickness required will be more than that of seamless material; so the E = 0.85 causes the allowable stress on the material to be lowered which will then drive up the required thickness. More material is required because we are only 85% sure that the welded material is as strong as seamless material or a Fully Radiographed butt welded joint.

another example: Required thickness for same material with the same pressure:

SEAMLESS t = 1 INCH

DOUBLE WELDED FULL RT t = 1 INCH

DOUBLE WELDED SPOT RT t = 1.15 INCHES

SE = 15,000 psi x 0.85 = 12,750 psi. The stress allowed in the calculation for thickness is now 12,750 psi and will result in the need for a thicker material in the vessel's construction.

Welding is costly and the thicker the material, the more costly the material and welding become.

Radiography has a cost and a benefit.

The direct cost is the cost of performing radiography.

The indirect cost is the cost of repairing the rejectable or defects revealed by radiography.

The benefit is the use of thinner material by increasing the Joint Efficiency ’’E’’ resulting in lower cost in material and welding.

Under certain conditions (depending on the joint location and type); full Radiography is required and the costs will be unavoidable.

The term Joint Efficiency as used today is really a measure of the quality of a joint. The Percentage of Radiography affects the Joint Efficiency ‘’E’’ which in turn affect the wall thickness ‘’t’’.

UW-12 Joint Efficiencies

UW- 12 states that the joint efficiency depends only on the type of joint and the degree of examination of the joint. The resulting joint efficiency shall be as given in Table UW- 12.

Butt Joints as attained by double-welding or by other means which will obtain the same quality on the inside and outside. Backing strip if used must be removed after welding is completed.

Type 1 Joint

Full RT: E = 1.0 ; Spot RT: E =0.85 ; No RT: E = .70

Type 2; CIRCUMFERENTIAL JOINTS

Full RT: E = 0.90; Spot RT: E =0.80; No RT: E = 0.65

Service Restrictions apply only to certain vessels (full radiography for lethal services).
Joint category is based on the joint location.
Type of joint is based on how the joint was fabricated (single butt weld, double butt weld, fillet weld).
Longitudinal Joint E, is the only Joint used for thickness calculations since this joint undergoes the maximum stress (twice of circumferential stress due to hoop stress).

UW-40 PP. 150; Procedures for Postweld Heat Treatment (PWHT)

Paragraph UW-40; PP. 150 gives the particulars of Postweld heat treatment while The minimum temperature for Postweld heat treatment given in Tables UCS-56-1 (PP. 172) through UCS-56-11

These paragraphs list the methods that are acceptable to the Code. For instance, UW-40 (a)(1) says that heating the vessel as a whole in an enclosed furnace is preferable and should be used if practical.

Heating the vessel in more than one heat in a furnace is also acceptable provided, an overlap of the heated sections shall be at least five (5) feet. Also, the portion outside the furnace shall be shielded to avoid large harmful temperature gradient or temperature difference.

The API 510 allows the use of Local Post Weld Heat Treatment that does not require the entire circumference of the vessel be included in the heat treatment. Obviously, this is aimed at field repairs.

In the API 510 Code, the PWHT procedure is required to be reviewed by a qualified engineer. There should be preheat applied in accordance with the material of construction.

The soak band shall include a circle that extends beyond the edges of the attachment weld in all directions by a minimum of t or 2"(50mm),whichever is less; it must include any nozzles or attachment welds in the local Postweld heat treatment area.

A suitable number of thermocouples (at least two) shall be used to monitor the temperature during treatment.

UCS-56 Requirements for Postweld Heat Treatment

Maximum furnace temperature at the time vessel or part is placed in it shall not exceed 800°F.

The rate of heating shall be increased is 400°F/hr (222°C/h) divided by the maximum metal thickness of the shell maximum.

Variation in the part temperature shall not be more than 250°F (140°C) within any 15 ft (4.6 m) interval.

The furnace design should not allow the flames to touch the part or vessel.

The depth of the repair based on the material P-number is restricted and non-destructive testing after removal of the defect is required.

An approved welding procedure is required and the repair must be made using the shielded metal arc process with low hydrogen electrodes.

The electrodes must be properly handled and the weave bead used is restricted to four electrode core diameters.

There are two repair techniques, namely, the Half Bead weld repair (when half of weld is removed after each pass) and Controlled deposition welding (CDW) is a joining technique to refine grains and to temper underlying heat affected zone (HAZ) in the base metal.

PART UG - GENERAL REQUIREMENTS

Candidates should understand and be capable of applying the following concepts.

Calculate the required thickness or pressure allowed on cylindrical shells using formulas based on vessel diameter or radius.
Calculate the thickness required or pressure allowed for 2:1 Ellipsoidal, Standard Torispherical and Hemispherical heads (Part MAWP).
Calculate the Thickness of Shells and Tubes Under External Pressure.
Determine Maximum Allowable Working Pressure for a Vessel.
Calculate Hydrostatic and Pneumatic Test pressures. Describe Procedures for Tests.
Size Fillet Welds at Openings.
Requirements for Name Plates and their markings.
Requirements for Material identification and Inspection.
Types of Data Reports. information contained in Data Reports.

UG-27 Internal Pressure Cylindrical Shells

For cylindrical vessel

The formula in UG-27 c 1: Circumferential Stress (Longitudinal Joints) having the highest stress, is the deciding formula:

t = PR/SE-0.6P

For Longitudinal stress (circumferential Joints

t = PR/2SE +0.4P

By comparing above formulas, you can see that the thickness for Longitudinal Stress (Circumferential Joints) shall be approximately half of Circumferential Stress (Longitudinal Joints).Please note that the stress is perpendicular to the direction of loading and hence , Longitudinal Stress (Circumferential Joints) and Circumferential Stress (Longitudinal Joints). If this looks confusing, just remember that longitudinal joint is more critical than circumferential jointSpherical shells have one formula only:

t = PR/2SE-0.2P

Problem # 1. Given a cylindrical vessel shell with the following variables, solve for pressure allowed in the cylinder. Please note that: R = inside radius of the shell course; if outside radius is given plus thickness, then R = RO – t.

P= ?; t= 0.500"; S= 15,000 psi; E= 1.0; R= 18.0" ; RO = 18.5”

P = 15000 X 1 X 0.5 / (18 + 0.6 X 0.5) = 7500 / 18.2 = 412. 08 psi

Answer: P= 412. 08 psi

Example 2. A cylindrical vessel shell has been found to have a minimum thickness of .353". Its original thickness was .375". what is the equivalent current pressure?

P= 300 psi ; t= 0.353" ; S= 13,800 psi ; E= 0.85 ; R= 12.0”

SEt = 13,800 x .85 x .353 = 4140.69; P = 338.46 psi 338.46 psi > 300 psi

ANSWER: YES

Problem # 2. Find the minimum required thickness of a cylindrical shell designed for a working pressure of 100 psi at 350 degrees F. The shell's inside radius is 2'-0". The longitudinal joint is category A (UW-3), type 1 (table UW-12) - no radiography was performed. The shell is made of SA-515 grade 60 carbon steel rolled plate with an allowable stress of 15,000 psi. The vessel is in water service. Again, circumferential welds are not considered for the sake of simplicity. Givens:

t= ? ; P= 100 psi ; R= 24" ; S= 15000; E= .70 (Table UW-12)

PR t = SE - 0.6 P 100 x 24 = 2400; (15,000 x .70)-(0.6 x 100) = 10440 t = 0.2298”

We have now calculated the pressure allowed on a seamless shell in Problem #1. We have also found the thickness required of a seamed, rolled plate shell in Problem #2. To this point we have not considered a circumferential weld joint. The next problem will consider joining together two courses of seamed and rolled plate to make one shell.

Problem # 3. Determine the minimum required thickness of a cylindrical shell designed for an internal pressure of 50 psi at a design temperature of 100 degrees F. No corrosion is expected. The shell is made of two courses butt welded circumferentially using Type 1 welds which have been spot radiographed. The shell longitudinal joints are butt welded also and are Type 1, Category A fully radiographed. The material is SA-515 grade 70, stress allowable is 17,500 psi. The inside diameter is 10'-0". Both heads will later be joined to the shell and will have Spot RT in accordance with UW-12(a) and UW-11(a)(5).

This problem will require us to consider two different cases in order to come to the solution. First we will work the problem to solve for the thickness required to resist longitudinal stresses. Second to resist circumferential stresses. Are you clear on the difference between the two? It's easy to be confused. The Longitudinal Stress is the stress that acts to pull apart two shell courses or pop a head off of the end of a vessel. It creates stress in the shell and welds around a vessel. Circumferential Stress can be thought of as trying to split a shell along its length. It creates stress in the shell and welds along the length of the vessel. Circumferential Stress is normally the controlling stress for thickness or pressure calculations.

Circ. Joint (Longitudinal Stress): Givens: t= ? ; P= 50 psi; D= 10'-0"; R= 5'-0" = 60”; S= 17500; E = .85 from table UW-12 PR t = 2 SE + 0.4 P 50 x 60 = 3000; t = 0.1007 = (2 x 17,500 x .85) + (0.4 x 50) = 29770 /3000 Long Joint (Circumferential Stress) Givens: t= ?; P= 50psi; R= 60"; S= 17500; E= 1.0 (UW-12(a) and UW-11(a)(5)) From UG-27 (c) (1) : PR t = SE - 0.6 P t = .1717”

Pressure Vessel Shell Design as per UG 27

UG-28 ; PP.19; Thickness Of Shells And Tubes Under External Pressure ; Overview

External calculations depart significantly from internal calculations simply because under external pressure the vessel is being crushed. Internal pressure wants to tear the vessel apart.

Because of the crushing or buckling load, the Length or height, the Outside Diameter and the Thickness of the vessel are important. External pressure problems are based on the thickness of the shell to the outside diameter ratio (slenderness ratio). There are two types of external pressure calculations required on the test: the O. D. (Do ) to thickness ratio (t) is greater than 10 and less than 10.

This type of problem is best approached from the in-service standpoint of view with an existing vessel. In order to solve these types of problems; two charts will be required. The first chart is used to find a value called Factor A and then Factor A is used to find a Factor B in the second chart. Once, the value of Factor B is found, it is used to solve the problem by the formula given in paragraph UG-28 (c)(1); step 6.

There will be no calculation type of question; you just need to know the above fundamentals for external pressure.

The inspector should be knowledgeable of the rules for design of shells and tubes under external pressure (UG-28). The inspector will not be required to perform external pressure calculations.

UG-20 Design Temperature; pp. 15

(a) Maximum The maximum temperature used in design shall be not less than the metal temperature expected under operating conditions. (b) Minimum The minimum metal temperature used in design shall be the lowest expected in service. Consideration shall include the lowest operating temperature, operational upsets, auto refrigeration, atmospheric temperature, and any other sources of cooling. (c) The design of zones with different metal temperatures may be based on their determined temperatures. (d) Impact testing per UG-84 is not mandatory for pressure vessel materials with P-No. 1, Gr. No. 1 or 2 and nominal thickness of: (a) 1/2 inch for materials listed in Curve A of Figure UCS-66 (b) 1 inch for materials listed in Curve B, C, or D of Figure UCS-66; Design temperature is no warmer than 650º F and no colder than -20º F; The thermal or mechanical shock loadings and cyclic loading are not a controlling design requirement. (See UG-22).

UG-98 Maximum Allowable Working Pressure Overview; pp.76

There are two types of Maximum Allowable Working Pressures (MAWP) in the Code .

One is for the vessel itself, the one most think of and refer to all the time. The other is the one for each part of a vessel referred to in UG-98 as the part MAWP.

Think of it in this way: a vessel has a shell, heads, chambers, nozzles, etc. The pressure allowed or thickness required calculations must be performed for each one to determine the MAWP of the vessel. When doing these calculations, you cannot take credit for any extra thickness designed into the vessel as a corrosion allowance. The weakest part of the vessels, considering loadings such as the static head of the contents, weight of insulation, wind, earthquakes, etc., will determine the MAWP of the entire vessel. It is the weakest link in the chain.

Please note that the MAWP as well as the test pressure; is the pressure measured at the highest point of the pressure vessel where as the bottom of pressure vessel tolerates the designated MAWP plus the static head, weight of the upper parts and other loads such as momentum during earth quake, wind load, etc.

The MAWP of a vessel is the pressure allowed in a vessel at its top in its normal operating position and at its Maximum operating temperature.

The MAWP is different when the operating temperature changes because the strength and therefore, the allowable stress of the materials are different at the different temperatures. Therefore, we need to use one designated operating temperature, for each temperature window based on the applicable allowable stress value.

UG-99 Standard Hydrostatic / UG- 100 Pneumatic Test Overview (PP. 77 & 78)

The requirements for hydrostatic and pneumatic tests brought in paragraphs UG-99 and UG-100.

These tests have many similarities but some important differences. Both of these tests can be applied to most vessels.

Please note that the preferred method of pressure test is by hydro test as it is safer because liquid is incompressible but the gas is compressible storing a lot of energy as a result that could cause damage to property and endanger human lives in case of failure.

In case of pneumatic test failure, the stored gas releases enormous energy and acts like bomb, that is why, there shall be barriers when pneumatically testing a vessel.

Most of the time, such vessels are tested in a water tank for added safety. Pneumatic test can be substituted for hydro test only if hydro test is not practical or feasible, for example, when the foundation under the vessel cannot hold the test medium when the vessel is fully filled with a test medium such as water.

Sometime, a combination of gas and liquid is used (50-50) and is called squeeze test. This is to reduce the danger of purely pneumatic test specially for larger vessels.

The following are the highlights of each type of pressure test from the approach of a repaired vessel by welding that been in service.

Hydrostatic

- If the test is required it shall be conducted after welded repairs.
- The test pressure must at least be 1.3 times of the MAWP for post 1999 vessels and 1.5 times of the MAWP for post 1999 vessels. Note; The test shall be conducted as per original revision of the code the vessel was constructed.
- The test pressure shall be adjusted for ratio of stresses. For example, if maximum allowable stress at 300ºF working temperature is 20,000 psi while at ambient temperature, MAWP is 25,000 psi, then, the test pressure is equal to: 1.3 X MAWP X 25,000/20,000 because pressure test is performed at ambient temperature and hence need to be adjusted accordingly. This is to simulate the test pressure at the operating temperature.
- Any non-hazardous fluid may be used if below its boiling point.
- It is recommended that the metal temperature during hydro test be maintained at least 30°F above MDMT for over 2” wall thickness and 10°F above MDMT for wall thickness 2” and less to minimize the risk of brittle fracture. Please note that ASME VIII uses 30°F above MDMT regardless wall thickness.

MDMT for all thicknesses where as API 510 uses 10°F and 30°F over MDMT for 2” and less and for over 2” shell wall thicknesses.

In case of any discrepancy between ASME VIII and API 510; API 510 inspection code requirement shall prevail.

Testing fluid must not exceed 120°F

- Following the application of hydro pressure; a visual inspection shall be performed at MAWP and not the test pressure. (possible exam question).

Pneumatic

- If the test is required, it shall be conducted after weld repairs.
- The welded repairs shall be subjected to the tests required by UW-50.
- The test pressure must at least be 1. 1 times the MAWP
- The test pressure shall be adjusted for lowest ratio of stresses. Ratio of the stress value S at its test temperature to the stress value S at its design temperature
- It is recommended that the metal temperature during hydro test be maintained at least 30°F above MDMT to minimize the risk of brittle fracture for over 2” wall thickness and 10°F above MDMT for wall thickness 2” and less. Please note that ASME VIII uses 30°F above MDMT for all thicknesses where as API 510 uses 10°F and 30°F for 2” and less and for over 2” thickness respectively.
- The test pressure shall be raised at a gradual rate to not more than 1/2 the test pressure and then raised by 1/10th of the test pressure until the test pressure is reached. Total of 6 steps.
- A visual inspection must be made at MAWP or the test pressure divided by 1.1.

The following written procedures will help to clarify the process. The ratio of stresses adjusts for the different strengths of materials at different temperatures. This will be explained during classroom instruction.

SAMPLE HYDROSTATIC TEST PROCEDURE

- Calculate the test pressure using the rules of UG-98 and UG-99.
- Any fluid in compliance with UG-99 may be used. The temperature of the testing fluid and the vessel shell shall be as described in UG-99 and API 510.
- Isolate openings as required by blinding.
- Install a calibrated gage of the proper pressure range as described in UG-102 directly to the vessel. If the gage is not readily visible to the operator controlling the applied pressure, an additional gage shall be provided where it will be visible to the operator throughout the duration of the test.
- If the test pressure will exceed the setting of lowest relief device, relief devices shall be removed , blinded or have test clamps installed.
- Vents shall be provided at all high points to purge air while the vessel is being filled.
- Before applying pressure, inspect all test equipment to insure it is tight and that low pressure filling fines and other appurtenances that should not be subjected to the test pressure have been disconnected.
- Warn all personnel in the area.
- Slowly raise the vessel to the test pressure. Hold for an appropriate time based on vessel size.
- Lower the vessel to the MAWP or test pressure divided by 1.3 and makes a visual inspection of all joints and connections.

UG-99 Calculating Hydrostatic Test Pressure

Question: Calculate the required hydro test pressure for a vessel using the following conditions.

Material SA-516 Gr. 65 Design Temp. 700°F Test Temp. 85°F MAWP 350 psi

(b) Per UG-99 the ratio equals Stress at Test Temp. / Stress at Design Temp. 16,300/15,500 = 1.05 Step 2: Per UG-99(b) Test pressure equals 1.3 x MAWP x Stress at Test Temp. / Stress at Design Temp. 1.3 x 350 psi x 1.05 = 477.75 psi

Answer: 477.75 psi at the top of the vessel.

Step 1: Determine the ratio of stresses for SA-516 gr. 65 for the test and design temperatures. (a). From Table 1A Section II Part D. Note: in the exam, you shall be given the allowable stress at working temperature and ambient or test temperature

Stress allowed at 700°F = 15,500 psi Stress allowed at 85°F = 16,300 psi

SAMPLE PNEUMATIC TEST PROCEDURE

Prior to administering a pneumatic test, ensure that the NDE of UW-50 for welded repairs has been performed successfully.

Calculate the test pressure using the rules of UG-98 and UG-100.

The metal temperature during pneumatic test shall be maintained at least 30°F above the minimum design metal temperature to minimize the risk of brittle fracture.

Isolate openings as required by blinding.

Install a calibrated gage of the proper pressure range as described in UG-102 directly to the vessel. If the gage is not readily visible to the operator controlling the applied pressure, an additional gage shall be provided where it will be visible to the operator throughout the duration of the test.

If the test pressure will exceed the setting of lowest relief device, relief devices shall be removed, blinded or have test clamps installed.

Before applying pressure inspect all test equipment to insure it is tight and that low pressure filling lines and other appurtenances that should not be subjected to the test pressure have been disconnected.

Warn all personnel in the area.

The pressure in the vessel shall be gradually raised to not more than one-half the test pressure. Thereafter, the test pressure shall be increased in steps of approximately one-tenth of the test pressure until the test pressure has been reached.

Lower the vessel to four-fifths the test pressure and hold for a sufficient time to make a visual inspection of all joints and connections

UG-100 Calculating Pneumatic Test Pressure

Problem: Calculate the required pneumatic test pressure for a vessel using the following conditions.

Material SA-516 Gr. 65; Design Temp. @700°F ; Test Temp. @ 85°F ;MAWP: 350 psi

Step 1: Determine the ratio of stresses for SA-516 gr. 65 for the test and design temperatures. (a). From Table 1A Section II Part D.Note: in the exam, you shall be given the allowable stress at working temperature and ambient or test temperatur

Stress allowed at 700°F = 15,500 psi Stress allowed at 85°F = 16,300 psi

(b) Per UG-99 the ratio equals (c) Stress at Test Temp. Stress at Design Temp.

16,300 /15,500 = 1.05

Step 2: Per UG-100(b) Test pressure equals 1.1 x MAWP x Stress at Test Temp. Stress at Design Temp.

1.1 x 350 psi x 1.05 = 404.25 psi

Answer = 404.25 psi

UG-100 Calculating Pneumatic Test Pressure

PROCEDURE FOR PNEUMATIC TEST

Slowly raise the pressure to approximately one-half 404.25 psi which equals 202.1 psi.
Raise the pressure in steps of one-tenth of the test pressure.

202.1 + 40.4 = 242.5 psi
275.5 + 40.4 = 292.9 psi
321.4 + 40.4 = 323.3 psi
367.3 + 40.4 = 363.7 psi
413.2 + 40.5 = 404.2 psi

c. Lower the pressure to MAWP (at ambient temperature) or pneumatic test pressure / 1.1 = 367.3 psi The adjustment for test and design temperatures is the reason why inspection is not taking place at the MAWP of 350 psi at operating temperature, i.e. 1.05 x 350 = 367.5 psi.

UG-102 Test Gages Overview

The Code has some definite requirements for the selection and uses of gages for the tests described in UG-99 and UG-100.

Directions for location, number of, range of and the calibration of the indicating gage(s) is located in UG-102.

The highlights of UG-102 are below.

An indicating gage shall be connected directly to the vessel. If it is not readily visible to the operator of the test equipment an additional gage shall be used which is visible to operator for the duration of the test.

When doing large vessel pressure tests; it is recommended to have a recording gage in addition to the indicating gage.

Dial type indicating gages shall have a range of about double the maximum test pressure, but the range of the pressure gage shall not be less than 1 1/2 times nor more than 4 times the maximum test pressure.

Digital gages having a wider range may be used as long as they provide the same or greater accuracy of the dial type.

All gages shall be calibrated against a standard dead-weight tester or a calibrated master gage.

Gages must be calibrated any time their accuracy is in doubt.

UG-99 / 100 / 102 Exercises

A vessel made of SA-240 304L plate is being hydrostatically tested after an alteration. The vessel's MAWP is 225 psi at 400°F. The allowable stress at operating is 14,700 psi and 16,700 psi at the test temperature.

Answer the following. Stress ration: 16700/14700=1.13

What is the required hydro test pressure? 1.136 X 1.3 X 225 = 332 psi
What is the required pneumatic test pressure? 1.136 X 1.1 X 225 = 281.2 psi
What is the least pressure the vessel can be inspected at? 332/1.3 & 281.2/1.1 = 255.6
In psi what is the minimum and maximum range of the test gage?

For hydro test: 498 – 1328

For Pneumatic Test : 421.8-1124.8

A pneumatic test of a vessel will be conducted to a pressure of 310 psi. Describe the steps for raising the vessel to the test pressure. At what pressure shall the visual examination take place?

1. 1. 310/2= 155 psi
  2. 155 + 31 = 186 psi
  3. 196 + 31 = 217 psi
  4. 217 + 31 = 248 psi
  5. 248 + 31 = 279 psi
  6. 279 + 31 = 310 psi

UW-16 Fillet Weld Sizing For Attachments At Openings (pp. 131)

The fillet weld sizing of UW-16 can be solved in either of two ways. That is, you may determine if a fillet weld leg size provides an adequate fillet weld throat size per Code or based on the thicknesses of the shell and nozzle determine the minimum throat size required and convert that to leg size.

In the latter case, usually the leg size decimal value is rounded to the next fractional 1/16th inch.

In these examples we will work it in both ways using the same shell and nozzle thicknesses. The examples will be restricted to only Fig UW-16.1 (i); PP. 133.

t1 + t2 = 1 1/4tmin.

t1 or t2 not less than the smaller of 1/4 in. (6 mm) or 0.7tmin.

Problem: A nozzle is being attached to a shell as shown in Fig. UW-16.1 (i) using two equal size fillet welds. The shell's thickness is 7/8 in. and the nozzle's thickness is 1/2 inch. The fillet welds are 3/8 inch in leg size. Does this meet Code? t = 7/8” tn = ½” t1 = 3/8” t1 = t2 = Leg Size 3/8” or .375” Case l.: Determine the minimum throat size. What is the throat size? Throat Size = 0.375 X 0.7 = 0.2625 From Fig. UW-16.1 (i) we are given that: t1 + t2 > 1 1/4 tmin And t1 or t2 not less than the smaller of 1/4 in. or .707 tmin From the nomenclature of UW- 16 we are given the following definitions: tmin = the smaller of 3/4 in. or the thickness of the thinner of the two parts joined by a fillet weld. t1 and t2 are the throat sizes of the welds as depicted in Fig. UW-16.1(i).

t1 = 7/8” t2= ½”

Step 1: Determine the throat size of a 3/8 in. leg size fillet weld.

Leg Size 3/8” or .375”

Throat size equals .707 times leg size. 0.707 x 0.375” = .265” Step 2: Determine tmin. tmin = the smaller of ½” or ¾” . So tmin. = ½”. Step 3: Determine if t1 + t2 ≥ 1 1/4 tmin

.265" + .265” ≥ 1.25 x .500"; .530" ≥ .625"

.530" is neither greater than or equal to .625". Therefore the first test fails and the throat size of the 3/8" leg fillet weld is too small,  We could stop here and answer the question with a No! But let's finish up with the second test of size required for an illustration of the technique required. Step 4: Test to see if: t1 or t2 not less than the smaller of ¼” or .707 tmin Not less than the smaller of .250” or .707 x ½” .707 x .500" = .3535" So not less than .250". Both t1 and t2 are .265". .265” > .250” Fillet welds are adequate in the second test. However a fillet weld size must pass both tests! Case 2.: Based on material thicknesses determine the minimum leg size of equal sized fillet welds to the next 1/16th inch. In our problem thicknesses are 7/8 inch (shell) and 1/2 inch (nozzle) . We have already determined that 3/8 inch leg fillet welds are too small. So let's determine what size of equal leg fillet welds are required rounded up to the next 1/16th inch.This is a case where you are really coming in through the back door; that is to say, you are not checking to see if an existing or proposed Fillet weld leg size is large enough. You are in fact determining the minimum size for a thickness combination. The approach is to set up the formulas given in Fig. UW-16.1 (i) and determine the minimum values so as to make the shoe fit. Step 1: Determine tmin.

tmin. = the smaller of ½” or ¾” So tmin = ½”

Step 2.: Determine .707 tmin

.707 x .500" = .353"

Step 3.: Determine 1 1/4 tmin. 1.25 x .500" = .625" From Fig. UW- 16.1 (i) we are given that: t1 + t2 ≥ 1 1/4 tmin And t1 + t2 not less than the smaller of ¼” or .707 tmin Let's stop and examine the formulas given above to make sure we understand what is being said. First, this business of throat 1 plus throat 2 being greater than or at least equal to 1.25 times tmin. .If that's the case, then to figure out the minimum throat size of one equal sized fillet weld, we need only calculate 1.25 x tmin and divide it by two. Next, what is really is being said in " t1 or t2 not less than the smaller of ¼” or. 707 tmin." is that the Code does not allow a fillet welds with a throat smaller than 1/4". This is to prevent a very large fillet weld on one side and what amounts to a small seal weld on the other side. This keeps the heat input balanced across the parts joined.

A: 1/4" throat requires a leg size of .353" about 3/8”. A: .625 / 2 = .3125 So .3125 + .3125 = 1 1/4 tmin.

B: .3125 > .250 ( t1 or t2 minimum size is satisfied)

C: To convert throat to leg, divide the throat by .707 .3125 / .707 = .4420 (Round up to the next 1/1 6th inch). 6 / 16th = .375 or 7/16th = .4375 or 8/16 = .500 .4375 < .4420 < .500

Answer: minimum leg size is 1/2 inch.

UW-16 Weld Size Determination Exercises

A fillet weld has a leg size of 1 1/8". What is its throat size?

1 1/8" X 0.7 = 0.7825

A fillet weld has a throat size of .600".What is its leg size rounded up to the next fractional 1/16"?

0.600/0.7 = 0.857” = 12/16”

UG-84 Charpy Impact Tests Overview

A major concern in vessel operations at low temperature is brittle failure of the material. This type of failure is considered more serious than a ductile failure simply because it is sudden, giving little warning (almost no bulging), and the material might shatter similar to a broken glass.

Impact testing is required to determine whether a material thickness at a given temperature is likely to fail in that manner. In other words, the goal of impact tests is to prove failure is unlikely with the thickness/material combination being used at a design pressure and the minimum design metal temperature (MDMT).

The term Low Temperature can be misleading. When welded, a 4" material thicknesses may be considered low temperature operation at 120°F. The first conclusion drawn from UG-84 must be that whether or not the tests are required.

For the API-510 candidate, impact testing applies to Part UCS Carbon and Low Alloy Steels of Sub-Section C. These steels are susceptible to brittle fracture even at fairly high temperatures. It should be concluded that impact tests are required on these materials and their weldments. The only exemptions are given in part UG-84 of the General Requirements and UCS66, 67, 68 and in UG-20(f). The search for exemptions for a given problem start in UG-20(f) and then continue through paragraphs UCS-66, 67, and 68. This process will be covered in Part UCS of this course.

UG-84 states that impact test shall conform to the paragraphs of SA-370. This is a reference to a standard listed at present on Table U-3 of Page 5 in Section VIII of Division 1. Look up this table and read it; It outlines the test apparatus and procedures. An open book question could come from here.

The only kind of impact test recognized by the Code is the Charpy V Notch type. The impact test specimens for a full size test are to be as shown in Fig. UG-84.

The next consideration is that of the minimum absorbed energy for the impact test specimen. Figure UG-84.1 is used to determine the value of absorbed energy required for a test specimen made of carbon and low alloy steels. Please note that it refers to those materials listed in Table UCS-23 and that the minimum specified yield strength and thickness of material or weld in inches; are crucial for determining impact absorbed energy.

The impact testing of the parts of a vessel falls into two general categories: materials and welds. A general statement can be made about these impact tests. If the base material being welded is required to be impact tested, the weld metal and its weld heat affected zone probably will also be required to be impact tested.

The weld metal and heat affected zones are impact tested using a production impact plate (normally, an extension of a welded joint on part of the vessel which can later be cut off to make the impact specimens). Please note that the Heat Affected Zone (HAZ) are the most vulnerable part for impact test due to high thermal stresses created on this area during the welding due to temperature difference between the molten weld and the base metal immediately next to weld pool, that is , the HAZ region.

The impact test specimen must be subjected to same heat treatments as the vessel. The location for removal of specimens from test plates are described in UG-84 (g). The thickness of a test plate determines the number of test specimens required and also the location of their removal from the test plate. See Figure UG-84.5 HAZ Impact Specimen Removal; pp. 71.

For test plates 1 1/2 inch or less; two sets of three (3) specimens must be taken. One set from the weld with the notch located in the weld as shown in Fig. UG-84 and one set from the heat affected zone (HAZ) with the notch located so that as much HAZ material as is possible is included in the resulting fracture.

For test plates over 1 1/2 inch; three sets of charpy impact test samples are required. One set from the weld metal and one from the HAZ. A third set is required to be taken from the weld metal as near as is possible to the centre of the weld.

The acceptance details for these impact tests is found in UG 84 (c)(5)(c)(6); and in the notes of Fig. UG-84.1. Figure UG-84.1 is used to determine the minimum acceptable absorbed energy for a set of test specimens. To use Figure UG-84.1, the material thickness is found along the bottom of the chart. From that point, move straight up to the line that represents the minimum yield of the material wider consideration, then left to the value of absorbed energy required to pass the test. Notice that this value is called an average. GENERAL NOTES at the bottom of the chart require that no one specimen shall have an absorbed energy value less than 2/3 of the average required for all three.

UG-84 Charpy Impact Tests Exercises

What type of Impact test does the Code recognize?

Charpy V Notch

What are the dimensions of a standard Charpy Impact specimen?

10 X 10 X 55 mm

How many specimens comprise a single set?

3

How many sets of specimens are required for a weld procedure test coupon 1 3/4 inches thick?

3

When welding a procedure test plate for impact testing what must the P No. and Group No. be? What type of heat treatment must be applied to the test plate?

Same as base metal, same as base metal

Name the two types of test specimens required for all welding procedures. Hint,. Where do they come from?

Weld & HAZ

UCS-66 Materials

Low temperature should always be a consideration when designing a vessel of carbon and low alloy steels specially for high thickness.

Example: Figure UCS-66 (5) (pp.181) shows that if the governing thickness of a non-welded part exceeds 4", and the minimum design metal temperature (MDMT) is colder than 120°F(50°C), then, the material shall be impact tested.

This example has been used to point out how relative the term low temperature is. Turn your attention to figure UCS-66 Impact Test Exemption Curves, In this figure you will find a graph and the list of carbon and low alloy steels.

UCS-68 Design; pp. 197

Two unequal thickness shall have a transition slope of 3:1 or more.

UCS-68 (a) (1)

30°F (17°C) reduction in impact testing exemption temperature is allowed if materials is post weld heat treated when not required by code.

UCS-68 (c).

UCS-66 Materials

If the material thickness is operated at or above the temperature listed in Table UCS-66, impact tests are not required.

If the material thickness is to operate below the given minimum temperature, impact testing is required.

The temperature found in the table is the MDMT of that material thickness without Impact Testing being required.

UG-77 Material Identification (pp. 63)

The material for pressure parts must be handled in a particular way per the Code. For instance, the Code specifies that materials for parts of a vessel should be laid out and marked in such a way as to easily maintain traceability after the vessel is completed.

Several techniques for identification markings are allowed and are described in this paragraph.

Stamping is the preferred method of marking vessel parts; however, as built drawings and tabulation sheets are also acceptable.

The manufacturer must maintain traceability to the original markings.

For instance, when cutting parts for the vessel from plate the heat number stamped on the plate should be transferred prior to cutting the plate.

A record of these markings must be maintained which will allow positive identification of the vessel parts after construction.

If a Code vessel manufacturer buys parts that are formed, such as heads, from another manufacturer of the head shall transfer the markings as applies to the material specification that the part is made from.

Only materials allowed by the Code can be used by the part manufacturer.

In addition. the part Manufacturer must supply a Partial Data Report (FORM U-2). The markings of the Part Manufacturer must be present on the part.

Note: FORM U-1 MANUFACTURER’S DATA REPORT FOR PRESSURE VESSELS (pp.620) FORM U-2 MANUFACTURER’S PARTIAL DATA REPORT (pp.628)

UG-93 Inspection of Materials (pp. 75)

The highlights of this paragraph are as follows:

Plate is the only pressure vessel material that must always have a Mill Test Report (MTR) or Certificate of Compliance (C of C) provided. The inspector shall examine these documents for compliance to the material specification.
All other product forms must be marked in accordance with their material specification. For examp1e, pipe marked SA- 106 gr. B.
All materials to be used in a vessel must be inspected before fabrication to find as best as is possible defects which would affect the safety of the vessel. The following describes the inspections required.

- Cut edges of and parts made from rolled plate to be inspected for laminations, shearing cracks, etc.
- Materials which will be impact tested, must be examined for surface cracks.
- The inspector must assure himself that thickness and other dimensions of the material comply with the requirements of this Division.
- The inspector must verify welded repairs to defects.
- The inspector must verify that all required tests have been performed and are acceptable (Impact tests, NDE, etc.).
- The inspector must confirm that there are no dimensional or material defects, perform internal and external inspections and witness pressure tests.

UG-116 Required Marking Overview (pp. 84)

The marking applied to a vessel's nameplate or directly to its shell are described in this paragraph. It is important information.

Often a vessel's Data Report is lost and the only information that is available is that found on the Name Plate or the shell itself. In some cases the Name Plate is missing or sand blasted and not readable.

The following is a listing of what is required by the Code to be present on the Name Plate.

The official Code U or UM symbol. If Inspected by the Owner/User of the vessel the word USER shall be marked on the vessel.
Name of the manufacturer preceded by the words "Certified by”.
Maximum allowable working pressure __________ psi at _______ °F.
Minimum design metal temperature _______ °F at ___________ psi.
Manufacturer's serial number.
Year built.
The type of construction used for the vessel must be marked directly under the Code symbol by the use of the appropriate letter as listed in the Code. Type of Construction Letter(s)

Arc or gas welded = W ; Pressure welded (except resistance) = P; Brazed = B; Resistance welded = RES

If a vessel is built using more than one type of construction; all shall be indicated.
If a vessel is in a special service the lettering as shown below must be applied. Lethal Service = L; Unfired Steam Boiler = UB; Direct Firing = DF ; Non-stationary Pressure Vessel = NPV
The MAWP must be based on the most restrictive part of the vessel. The weakest link and gage placed at the highest point during pressure test.
When a complete vessel or parts of a vessel of welded construction have been radiographed in accordance with UW-11, the marking must be as follows:

“RT 1” When all pressure retaining butt welds, other than B and C categories (associated with nozzles and communicating chambers that neither exceed NPS 10 nor 1 1/8” thickness) have been radiographically examined for their full length in a manner prescribed in UW-51.
“RT 2" Complete vessel satisfies UW-11 (a)(5) and UW-11 (a)(5)(b) applied.
“RT 3” Complete vessel satisfies spot radiography of UW-11 (b).
“RT 4” When only part of the vessel satisfies any of the above.

*A separate section follows which is devoted to the meanings of RT markings:

The letters HT must be used when the entire vessel has been Postweld heat treated.
The letter PHT when only part of the vessel has been Postweld heat treated.
Code symbol must be applied after hydro or pneumatic test.
Parts of vessels for which Partial Data Report are required shall be marked by the parts manufacturer with the following:

"PART" Name of the Manufacturer The manufacturer's serial number.

Note: These requirements do not apply to items like manhole covers, etc.16. All required markings must be located in a conspicuous place on the vessel, preferably near a manhole.

UG-119 Nameplates (pp. 88)

In this paragraph are the details of nameplates, including such things as the size and methods of markings allowed is explained. An additional nameplate may be used if it is marked with the words " DUPLICATE ".

It should bear the sign ‘’ U’’ stamp.

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ASME Section VIII Pressure Vessel Construction Code by Section - YouTube

Typical Nameplate:

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