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Wastewater Treatment: Definition, Process Steps, Design Considerations, Plant Types

Written by Anup Kumar Dey in Civil

Wastewater treatment is a process to treat sewage or wastewater to remove suspended solid contaminants and convert them into effluent that can be discharged back to the environment with acceptable impact. The plants where the wastewater treatment process takes place are popularly known as Wastewater treatment plants, Water resource recovery facilities, or Sewage Treatment Plants. Pollutants present in wastewater can negatively impact the environment and human health. So, these must be removed, broken down, or converted during the treatment process. Typical pollutants that are normally present in wastewater are:

  • Bacteria, viruses, and disease-causing pathogens.
  • helminths (intestinal worms and worm-like parasites)
  • Toxic Chlorine compounds and inorganic chloramines.
  • Metals possessing toxic effects like mercury, lead, cadmium, chromium, and arsenic.
  • Decaying organic matter and debris.
  • oils and greases.
  • Toxic chemicals like PCBs, PAHs, dioxins, furans, pesticides, phenols, etc.
  • Some pharmaceutical and personal care products.

How is wastewater formed?

A number of activities help in the formation of wastewater. Domestic wastewater is generated because of activities like bathing, washing, using the toilet, etc in residences, restaurants, and businesses. Surface rainwater runoff is generated due to the mixing of debris, grit, nutrients, and various chemicals. Industrial wastewater results because of chemical and manufacturing industry discharges. So, wastewater is essentially the used water that has been affected by domestic, commercial, or industrial use.

Domestic wastewater is relatively easy to treat as compared to industrial wastewater due to its high-strength nature.

Wastewater Treatment Process

The sequence of wastewater treatment processes is usually characterized as:

  • Preliminary treatment
  • Primary treatment
  • Secondary treatment
  • Tertiary treatment or Advanced treatment

Preliminary treatment:

Preliminary wastewater treatment precedes primary treatment. Its main function is to minimize operational problems and to protect subsequent treatment units. The major processes that are used during the preliminary wastewater treatment process are Equalization, Neutralization, Temperature adjustment, Screening, Grit removal, etc.

Primary treatment:

The primary wastewater treatment process is the physical or chemical treatment for the removal of materials that will either float or readily settle out by gravity. The major processes used in this step are Sedimentation and Dissolved air floatation. Suspended solid materials from the wastewater are removed by the sedimentation primary treatment. Other floatable materials like oils, fats, etc are removed using dissolved air floatation treatment. Primary wastewater treatment, in general, removes about 60% of suspended solids from wastewater.

Secondary treatment:

Secondary wastewater treatment uses biological and chemical means for the substantial elimination of dissolved organics and colloidal materials. The processes used in the secondary treatment are Activated sludge, Aerated Pond, Aerobic-anaerobic ponds, Trickling filter, Chemical oxidation, Chemical mixing flocculation and clarification, Gravity filtration, Dissolved-air flotation with chemicals, Pressure filtration, Anaerobic contact, etc. Secondary wastewater treatment is capable of removing more than 90 percent of suspended solids.

Advanced treatment:

Advanced wastewater treatment is used to remove pollutants by methods other than those used in conventional treatment methods mentioned above. The advanced wastewater treatment process employs a number of different unit operations like Activated carbon adsorption, Micro straining filtration, ponds, post-aeration, Land treatment, membrane solids separation, and specific treatment processes such as phosphorus and nitrogen removal, etc.

Very high effectiveness is the characteristic of the Advanced wastewater treatment process. That’s why this method is employed to meet strict effluent standards. For example, Phosphorus levels of less than 1 milligram per liter and total nitrogen levels of 5.0 milligrams per liter or less can be maintained through an advanced wastewater treatment process.

Basic Wastewater Treatment Processes
Fig. 1: Schematic of Basic Wastewater Treatment Processes

Basic Design Considerations

Wastewater Treatment Requirement: The requirement of wastewater treatment is dependent on the following parameters:

  • the influent characteristics,
  • the effluent quality requirements, and
  • the wastewater treatment processes that produce an acceptable effluent.

Laboratory tests of wastewater samples are performed to find out influent characteristics. Effluent quality requirements are fixed by Federal, interstate, State, and other local regulatory agencies. Wastewater Treatment processes are then decided according to influent-effluent constraints and economic and technical considerations.

The Capacity of Wastewater Treatment: The capacity of wastewater treatment is decided based on the design population and multiplying it with the proper capacity factor. Design population is found by adding total residents with 1/3 the non-resident populations. The following image (Fig. 2) provides a sample table of capacity factors with respect to effective population.

Capacity factors with respect to Effective Population
Fig. 2: Capacity Factors with respect to Effective Population

Future service demand calculation: Per capita waste loads of a community are decided based on the nature of the activities as different activities have different water uses. The table in Fig. 3 provides a typical example of sewage flows in gallons per capita per day (gpcd).

Per capita sewage flow example
Fig. 3: Per capita sewage flow example

Estimating the volume of wastewater:

The required average daily wastewater flow for the design of new wastewater treatment plants needs to be calculated by multiplying the design population by the per capita rates of flow as determined from the table in Fig. 3.

To calculate contributing populations, a factor of 3.6 persons per family residential unit can be considered. For hospitals, the calculation can be done by counting the number of beds, plus the number of hospital staff eating three meals at the hospital, plus the number of shift employees having one meal there. This total is the number of residents to be used in the design calculations. The capacity factor still needs to be applied while calculating design populations.
To find the volume of industrial flow, actual measurements can be done to ascertain the flow rates. Typical industrial discharges include wastewater from the following:

  • wastewater treatment plant itself;
  • vehicle wash areas;
  • maintenance facilities;
  • swimming pool backwash water;
  • weapons cleaning buildings;
  • boiler blowdowns;
  • photographic laboratory;
  • water treatment plant backwash;
  • cooling tower blowdown;
  • fire fighting facility;
  • medical or dental laboratories.

When significant inflow enters the sewer system, storm-water flows should be included in wastewater treatment plant design.

Once, all the above data is calculated, the following equation is used to estimate the total anticipated flow to the sewage plant:

x = a + b

Where
x = Total flow to sewage plant
a = Flow from population (effective population × 100 gpcd × capacity factor)
b = Infiltration + industrial wastewater + storm-water (4 × dry-weather flow)

The following image (Fig. 4) provides a typical flowchart for Wastewater treatment processes.

Flowchart for Wastewater treatment processes
Fig. 4: Flowchart for Wastewater treatment processes

Types of Wastewater Treatment Plants

For the betterment of society, the environment, and the future, wastewater treatment should be taken seriously. The outbreak of numerous waterborne diseases can be prevented by proper wastewater treatment. So, Wastewater treatment plants play a major role in keeping the environment clean and saving numerous lives. There are basically three types of Wastewater treatment plants:

  • Effluent Treatment Plants
  • Sewage Treatment Plants, and
  • Combined Effluent Treatment Plants

Effluent Treatment Plants are used by major chemical, leather, and pharmaceutical companies to purify water and remove dirt, grit, pollution, toxic, and non-toxic materials, polymers, etc. The typical processes used by Effluent Treatment Plants are centrifuging, filtration, incineration for chemical processing, and effluent treatment.

Sewage treatment plants eliminate contaminants from wastewater and household sewage. It uses physical, chemical, and biological processes to remove physical, chemical, and biological contaminants to make water and solid waste reusable.

Combined Effluent Treatment Plants are established where a cluster of small-scale industries is present. Such facilities reduce the cost of a single company while preventing pollution.

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What is a Framework Agreement? | Difference between Framework Agreements and Framework Contracts

Written by Anup Kumar Dey in Piping Interface,Procurement,Project Management

A framework agreement can be defined as an agreement between two or more business organizations (contracting parties or suppliers) that recognizes the agreement on enough matters to move forward with the relationship, with more details that will be agreed to in the future. However, this is not a final agreement on all matters relevant to the relationship between them. In a framework agreement, the governing terms and conditions for any future contracts with regard to the price, service levels, quality, scope, and quantity are normally established for the duration of the agreement.

Such agreements create a long-term relationship with the parties to carry out work mutually. Setting up a framework agreement between organizations is a highly efficient way of working together. The actual tendering process and the time taken for those processes can be saved. In a framework agreement, work is normally awarded to a bidder after running a mini-competition. This reduces the time required and the complexity of those works. Framework arrangements are a very convenient mechanism used widely to establish a suitable trading relationship between organizations.

As Framework arrangements represent a ‘smarter’ way of purchasing as compared to placing ‘one-off’ orders for recurrent contracts, It is becoming more popular. A buyer simply uses the agreement and issue a separate order considering the term and conditions of the framework agreements. Framework agreements are also known as ‘trading agreements’, ‘standing offers’, ‘umbrella agreements’, or ‘blanket orders’.

Framework Agreement
Framework Agreement

Why use a framework agreement?

A framework agreement is a useful way of obtaining goods and services that are regularly or
periodically required. It allows the purchaser to aggregate the future, anticipated requirements and thereby improve the purchaser’s negotiating position based on the likely economies of scale. In addition to the savings in cost, framework agreements also save time and effort by eliminating the need to run separate competitive tendering exercises for each requirement.

In framework agreements, the client/procurer asks a large number of firms (for example 20 firms) to submit details of their ability in terms of various qualitative factors (like experience, capability, safety qualifications, cost, etc) and then selects a small number of firms (normally 2-5) tenderers, to be in that framework. All subsequent jobs are then allocated by conducting a ‘mini-tender with this small number of firms and finally awarded to the most effective bidder in terms of cost and capability.

Duration of a framework agreement

The time duration for a framework agreement depends on the buyer or the client. Normally it can vary in between 2 years to 10 years.

Advantages of a framework agreement

A framework agreement is a great way to work between organizations. All the parties under the agreement get several benefits like:

  • It nourishes a long-term relationship.
  • The project or work awarding process becomes simple and less time-consuming. No need for numerous proposal preparation.
  • Process and contract terms are defined beforehand so it is not required to decide for each individual project or job.
  • Future jobs are known beforehand so easy for planning.
  • Possibility of being awarded multiple contracts.
  • Competitive pricing and on-time delivery.
  • Enables the use of e-procurement/portals by putting the suppliers’ offerings under the framework arrangement on a system accessible by all to use.
  • A planned approach reduces administration time and costs, thus increasing profit for all parties.
  • More flexibility of working.
  • Less downtime between identifying a need and fulfilling it
  • Potentially reduce the need for repeated requisitions and approvals to be processed.
  • Eliminates the need to carry out separate procurement exercises every time.
  • Good technical service with reliable quality.

However, the main rationale behind using a framework agreement is to achieve cost savings by creating economies of scale, as well as by reducing the administrative burden of issuing multiple tenders. That’s why central purchasing bodies use framework agreements as the main tool.

Disadvantages of a framework agreement

  • As the Framework agreement is based on future implementation, it is full of risks and uncertainties.
  • A framework agreement being a long-term contract, new potential suppliers or SME companies do not get access to offer their services. Also, Suppliers unsuccessful at the selection stage are locked out of any call-offs for the duration of the agreement.
  • Bigger Contracts.
  • Even after awarding the framework, still, hard work and networking are required to win specific jobs. No guarantee of business even if you’re selected as an approved supplier.

Framework agreement process

Normally, there are three steps for a framework agreement process to work effectively. Those are

1. Consideration for Framework Agreement:

The type of framework is determined by taking into consideration of the circumstances, risks, economic environment, etc. All required information is provided for example:

  • A description of the purpose and scope of the arrangement
  • Clearly state whether it is a contract or agreement
  • Stipulate the terms and conditions that apply to each call-off
  • Define the requirements – specifications, standards, Service Level Agreement (SLA)
  • Identify the pricing mechanism
  • Outline the call-off mechanism/procedure
  • State the term or duration of the arrangement
  • Identify any limitations on the use of the arrangement
  • If appropriate, provide a realistic estimate of volumes

2. Establishing framework agreements

When considering how many suppliers to award a framework arrangement to it may be necessary to consider the potential geographical coverage or, for a multi-disciplinary requirement, the specific components in the scope may need to be considered and broken down, and awarded separately. Another consideration may be to allow suppliers to subcontract work, but it should be made clear that in the terms and conditions that the main supplier awarded any work shall remain totally liable for their sub-contractor’s performance.

When tendering frameworks, the tender documentation should clearly state that our intention is to establish a
framework arrangement; stating the duration of such arrangement; indicate the estimated maximum number
of suppliers; potentially identifying the estimated total value and an outline of the award criteria.

3. Monitoring framework arrangements

Frameworks agreements and contracts with suppliers need to be properly managed, through regular performance reviews with the supplier and should consider the supplier’s performance, any pre-agreed remedial actions, and continuous improvement as well as include feedback from the key business users and the suppliers themselves.

The performance should be measured in line with the agreed metrics in the terms and conditions when the agreement was first established or re-let. The definition of the metrics and management information should be clear and include all aspects that are important (e.g. delivery performance; minimum system up-time etc.) and state which party will capture the metrics. Often, the supplier is in the best position to do this.

Difference between Framework Agreements and Framework Contracts

Often, Framework agreements are mistakenly referred to as ‘contracts’. But there are distinct differences between the two. A contract is a legally binding agreement between two parties that commits them to exchange goods and/or services in return for money. Whereas, a framework agreement is a different concept. In general, this does not include a legally binding commitment on the customer to receive any of the goods/services and to make payment. Framework agreements only give the outline terms and conditions through which the customer can place one or more individual orders, only then is there a contract between the customer and the supplier. The major differences between a framework agreement and a framework contract are:

Framework AgreementFramework Contract
This is a consideration/arrangement for future contracts with stipulated terms and conditions.This is the actual contract for a specified period.
Normally, money is not involved at this stage. No up-front fee payment.Money is involved.
Not legally bindingLegally binding.
The amount of work or supply is not specifiedVolume is specified.
The framework agreement is the main contract.Framework contracts are each individual mini-contracts.
Framework Agreement vs Framework Contract

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What is Material Safety Data Sheet (MSDS)? | MSDS VS SDS

Written by Anup Kumar Dey in Health & Safety

An MSDS or Material Safety Data Sheet is a technical document containing detailed and comprehensive information on the potential hazards related to health, fire, reactivity, emergency, and environmental issues. MSDS is an essential health and safety program that focuses on safe working with chemicals, hazardous materials, medical waste, or other toxic materials. The material data sheet provides all the hazard or safety information on the storage, use, handling, and emergency procedures of the material. These are mostly prepared by the manufacturer or supplier of the product and tell about the hazardous effects of the chemical, their safe usage procedure, handling information in case of accidents, etc. MSDS follows the requirements of WHMIS (Workplace Hazardous Materials Information System) legislation, Canada, and OSHA’s Hazard Communication Standards (HCS). The main purpose of this document is to assist employees in understanding and interpreting this type of information.

As per the requirement of the Hazard Communication Standard (HCS), the manufacturer, distributor, or importer of chemical products should provide Material Safety Data Sheets for each hazardous chemical to all downstream users. These MSDSs are specific to each individual chemical covering all reasonably anticipated uses of the material. The information furnished in an MSDS is normally general in nature but is organized into either 9 or 16 sections.

Suppliers and Employers’ Responsibilities related to MSDS

It is the responsibility of the chemical suppliers to obtain or develop an MSDS for each product to be used in the workplace. They must ensure that the MSDS for the specific product contains the latest information during the time of sale (not older than 3 years).

Similarly, the employer should confirm that he receives an up-to-date latest MSDS from the supplier. They should maintain the MSDSs and ensure that a copy of the same is readily available for the workplace. They need to train their employees regarding the procedures of safe use, storage, handling, and disposal of those chemicals.

Difference between MSDS and SDS

Safety Data Sheet or SDS is the latest updated form of earlier MSDS. This transition from MSDS to SDS came into effect from May 2012 onwards. The main differences between SDS and MSDS are

  • SDS format provides more in-depth information as compared to MSDS and consists of sixteen sections providing specific information using a standardized classification method. Earlier MSDS used to have nine categories which have been replaced by 16 sections in SDS.
  • MSDS was mainly meant for Canada whereas SDS is applicable on a global level following a Globally Harmonized System of Classification and Labelling of Chemicals (GHS).
  • By changing from MSDS to SDS, information is now produced in a standardized, user-friendly way.
  • With respect to the legal implications, An SDS adheres to all of the major regulations on hazardous materials and is a safer document to use.

Contents of an MSDS

MSDS formats can vary from source to source within a country depending on national requirements. However, A material safety data sheet is normally organized into sixteen sections. Sections 1 through 8 give general information regarding the chemical, its identification, composition, hazards, safe handling practices, and emergency control measures. While Sections 9 through 11 and 16 contain other relevant scientific and technical information. An MSDS is reviewed every three years.

MSDS Categories

There are nine categories in an MSDS that include the following:

  • MSDS Category 1-Product Information: product identifier (name), manufacturer and supplier names, addresses, and emergency phone numbers.
  • MSDS Category 2-Hazardous Ingredients.
  • MSDS Category 3-Physical Data.
  • MSDS Category 4-Fire or Explosion Hazard Data
  • MSDS Category 5-Reactivity Data: information on the chemical instability of a product and the substances it may react with.
  • MSDS Category 6-Toxicological Properties: health effects.
  • MSDS Category 7-Preventive Measures.
  • MSDS Category 8-First Aid Measures.
  • MSDS Category 9-Preparation Information: who is responsible for the preparation and date of preparation of MSDS.

SDS Sections

There are sixteen sections of any SDS. Those are:

  • SDS Section 1- Product and Company Identification: In this section, the product identifier of the hazardous substance and its recommended uses are mentioned. It must also include the name, address, and contact information of the manufacturer, importer, or other responsible parties.
  • SDS Section 2- Hazards Identification: The Hazards Identification section warns about the different ways of that chemical exposure and the harmful effects that it can have.
  • SDS Section 3- Composition/information on ingredients: This section provides information on the composition of the substance and trade secret claims associated with it.
  • SDS Section 4- First-Aid Measures: Necessary first aid information on accidental exposure of the chemical is mentioned in this section.
  • SDS Section 5- Fire-Fighting Measures: Recommendations for fire events caused by the chemical are provided in this section.
  • SDS Section 6- Accidental Release Measures: This SDS section provides guidance to minimize exposure to people or assets due to accidental spills, leaks, or releases.
  • SDS Section 7- Handling and Storage: Safe handling and storage recommendations are detailed in this SDS section.
  • SDS Section 8- Exposure Controls/Personal Protection: To minimize worker exposure, this SDS section provides information on the exposure limits, engineering controls, and personal protective measures.
  • SDS Section 9- Physical and Chemical Properties: Various physical properties like Appearance, pH, Odor, Flammability, Flash Point, Density, Viscosity, Ignition temperature, etc are mentioned in this section of the SDS.
  • SDS Section 10- Stability and Reactivity: Data related to the chemical stability and reactivity hazards of the chemical is described in this section.
  • SDS Section 11- Toxicological Information: Toxilogical and health impacts are mentioned in this section.
  • SDS Section 12- Ecological Information: This section guides the information on the environment in case of the release of the chemical.
  • SDS Section 13- Disposal Considerations: To reduce potential exposure, this section suggests proper disposal practices and safe handling methods.
  • SDS Section 14- Transport Information: Information related to transport hazard class, packing group number, bulk transportation, precautionary measures, etc are mentioned in this section.
  • SDS Section 15- Regulatory Information: Safety, health, and environmental regulations of the specific chemical is identified in this section.
  • SDS Section 16- Other Information: Information related to manufacturing dates, revisions, or any other useful information is added in this SDS section

Safety Data Sheets must be provided for:

  • Chemicals (substances and mixtures) that are considered hazardous in accordance with Regulation (EC) No 1272/2008.
  • Substances that meet the criteria as persistent, bio-accumulative, and toxic (PBT) or very persistent very bio-accumulative (vPvB) to the environment in accordance with REACH
  • Substances that appear on ECHA’s Candidate List of substances of very high concern (SVHC) for a reason other than either of the two points above
  • Mixtures (upon request of the downstream user/ distributor) which themselves are not classified under CLP but which contain at least one substance that is:
    • classified as hazardous to health or the environment above concentration limits set out in Article 31(3) of REACH;
    • a PBT or vPvB at a concentration ≥0.1% w/w;
    • on the Candidate List of SVHCs at a concentration ≥0.1% w/w for a reason other than either of the two points above;
    • assigned an EU limit value for exposure at the workplace (OELV).

What is in an MSDS?

A Material Safety Data Sheet or MSDS lists the hazardous ingredients present in a product. It provides a detailed report of the physical and chemical characteristics of a product and its effect on human health. MSDS also lists the chemicals which adversely react with the product. The precautions that need to be exercised while handling the product and the types of measures required to be used to control exposure, emergency, and first aid procedures, etc are also presented in an MSDS.

How do I get MSDS sheets?

MSDS related to the purchased product must be supplied by the manufacturer. In general, there are two options to get an MSDS. They are:

  1. An MSDS in form of a paper copy or e-mail attachment can be sent along with the product.
  2. Manufacturers can upload the MSDS to their websites for users to download from there.

Why is MSDS so important?

An MSDS is very important as it provides detailed information about the potential hazard that the product may cause. Knowing all such hazards beforehand will increase safety at the workplace.

Who is responsible for safety data sheets?

As per the Hazard Communication Standard, chemical manufacturers, distributors, or importers are responsible for providing the safety data sheets to the buyer.

Are MSDS required for all chemicals?

An MSDS is required for all potentially hazardous chemicals. However, if the chemical is not hazardous, it may be exempted. In general, all chemicals used at worksites that have any potential to cause hazards must have an MSDS.

Where can I get MSDS sheets online?

The online website of VelocityEHS contains the safety datasheets of all industry-leading chemicals. You can visit their website https://www.ehs.com/resources/sds-search/ and search as SDS using the product name, manufacturer, CAS, or Product Code.

Is MSDS required for shipping?

Yes, for all potentially dangerous items, an MSDS must be provided for every single shipment.

Why is it important to know your safety data sheet?

Knowing SDS is important because one must know the hazards of the products he is using. It will help him to protect himself during emergency situations.

What are the 4 main purposes of an SDS?

An SDS serves four main purposes. They are:

  • Product and Supplier identification.
  • Identification of the potential hazard related to the product.
  • Prevention, and
  • Response.

When should you read an SDS?

The SDS must be reviewed at least once every 5 years. It must add any new data as soon as they are available.

When did MSDS change SDS?

Effective from June 1, 2015, all Material Safety Data Sheets (MSDS) of potentially hazardous products are changed with new Safety Data Sheets (SDS).

How long do you need to keep SDS sheets?

OSHA standard, 29 CFR 1910.1020, requires all employee exposure records to be maintained for at least 30 years.

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Piping Installation and Erection Procedure

Written by Adarsh in Construction,Piping Design Basics

Piping Installation or Erection refers to the laying of the piping system and its related accessories to make it ready for fluid transfer. Proper piping installation following the codes and standards is the key to safety and good operation. It is the next step to piping fabrication, where pipe spools are made in the fabrication shop by cutting the pipes to the correct lengths and requirements. These prefabricated pipe spools are taken to the site or plant for assembly. This assembling of piping spools in the site following isometric or piping general arrangement drawings is referred to as piping erection. The piping coordinates are matched with the drawings during the piping installation.

Inputs Required for Piping Installation

Piping installation at the construction site is done following proper engineering work methods and drawings. The main inputs referred to during piping erection are:

P&ID is the heart of piping; it includes pipeline number, size, material, and insulation; Process condition & physical data, operation condition, streamflow details, Equipment numbers, etc.
Piping Isometric drawings include proportionate drawings with exact dimensions represented, line numbers, pipe fittings, valves, flanges, special components, tables including a list of all fittings in the drawings, etc.

Piping GA drawings include the locations of the main equipment in the plant, main piping items, fittings and valves, nozzle orientation of the concerned equipment, etc. Fig. 1 below shows typical drawings required for piping installation and a piping erection and installation flow chart.

Piping Installation Flowchart and Input Drawings
Fig. 1: Piping Installation Flowchart and Input Drawings

Piping Installation Procedure

Piping Installation normally starts after civil supports are erected and major types of equipment are placed on the construction site. The installation of piping can be grouped into the following parts:

Pipework Erection Procedure

Proper planning should be made to erect piping, area-wise following piping isometric and GA drawings. The following piping erection guidelines should be followed:

  • All tools, equipment, ropes, and pipes must be inspected and certified by HSE guidelines before erection to ensure that they are safe and ready, clean, and free from loose contamination.
  • Pre-fabricated spools need to be identifiable and numbered/tagged.
  • Pipework should be erected on supports designated for the specific line. Primary pipe supports can be welded prior to erection following pipe support drawings. The number of temporary supports shall be minimized.
  • Undue stresses should not be applied to force the piping to keep it in the proper place.
  • To avoid the ingress of moisture and foreign matter, pipe openings should be sealed during erection.
  • Installation of piping on pipe racks should be done from lower elevation to higher elevation.
  • Large-bore piping shall be installed prior to small-bore piping.
  • Piping Joints shall be properly aligned.
  • Pipe clearances from other pipes, equipment, and structures should be maintained.

Installing Piping Flanges

Clean pipe flanges should be brought up flush and square without forcing them to bear uniform bolt tension and gasket compression. Line items like orifice flanges, spectacle blinds, strainers, etc. shall be installed following proper orientation. A logical bolt tightening (hydraulic bolt tensioning & torque tensioning) sequence needs to be followed.

The flange connections to this equipment shall be checked for misalignment, excessive gaps, etc. Until both side flanges are ready for mating connection, flange covers shall be retained on all flanged connections to the valve or equipment.

Extra care is to be exercised for flange connections to pumps, turbines, compressors, cold boxes, air coolers, etc. Blanks or spades should be used on equipment to prevent the ingress of internal pipe debris. Bolting shall move freely through accompanying bolt holes at the right angle to the flange faces and a clear gap between the two flange faces for the gasket needs to be maintained before gasket installation.

Pipe Support Installation

  • Relevant pipe support detail drawings should be used for installing pipe supports.
  • Additional stress should not be introduced to fit the supports.
  • The pipe shoe should be installed at the center of the beam without any offset.
  • Where spring supports are required, those should be locked until hydro testing and insulation. Manufacturer installation guidelines should be followed.
  • Where PTFE plates are used for friction reduction, the ingress of sand in between SS and PTFE plates should be avoided.
  • Piping is to be arranged to facilitate pipe-supporting and shall be well-planned for ease of removal of equipment for inspection and servicing.

Pressure Testing

Following the guidelines, hydrostatic or pneumatic testing should be performed to check the system’s integrity. In case of leakage, those are repaired and re-tested again. Click here to learn more about Pressure testing

Insulation and Painting

After pressure testing, bare pipes and painted as per specification. High-temperature lines are insulated following the insulation procedure.

Marking and Identification

All pipes and fabricated fittings are marked on their outside with letters and numbers for easy identification of lines, their services, etc. Marking is normally done by stamping, tagging, stenciling, or using any other permanent marking method.

Installation of Expansion Joints

Expansion joints are normally required for critical piping systems. Bellows should be installed following the vendor’s guidelines and installation drawings. Piping should be perfectly aligned with the expansion joint as mentioned in the detailed drawings.

Vents and Drains

Ideally, vents and drains should be located in the isometric drawing or GA drawings. In case, high-point vents and low-point drains are not provided in those drawings, these should be provided as per the instructions of the Engineer-in-Charge/Job standards/ Piping Specifications.

Installing Underground Pipes

  • Before starting buried pipe installation, it must be ensured that trench excavation is done following the approved drawing.
  • Final measurements, tests, and surveys are to be completed before backfilling.
  • The depth of cover as mentioned in the GA drawings should be maintained.

Equipment and Tools for Pipe Erection

The following equipment and tools are used for piping erection and installation purposes.

  • Welder’s gauge
  • Pipefitters square
  • Fitter grips
  • Centering head
  • Flange aligners
  • Pipe wraps
  • Pipe clamps
  • Pipe cutter
  • Pipe stands
  • Water hose
  • Welding machine
  • A-frame
  • Adjustable wrench
  • C clamp
  • Center punch
  • Chain block
  • Forklift
  • Steel tape
  • Tower crane
  • Boom lifter
  • Cranes
  • Spanners and Torque Wrenches

Safety during Piping Installation

“SAFETY FIRST” is the primary concern of engineers. Hence, the safety of the people should override all other targets and achievements. Any unsafe situation should immediately be reported to the HSE manager and the work should be postponed. So the following guidelines should always be observed during piping installation and erection.

  • Identifying the hazards associated with piping services. This is mainly concerned while working in operating plants.
  • Understanding the color codes: Pipes are normally colored following standard guidelines to identify based on fluid service categories. The following image (Fig. 2) provides a sample color-coding table based on the BS 1710 standard.
  • Exercise extra care while tying a pipe to an operating system.
  • Use proper safety guidelines while working at heights and confined spaces.
  • Always be aware of what can go wrong and what to do if things go wrong.
  • Personal safety equipment must always be carried.
Piping colors as per BS 1710
Fig. 2: Piping colors as per BS 1710

Heat Affected Zone (HAZ): Definition, Causes, Effects, Color Bands, Reduction

Written by Anup Kumar Dey in Civil,Construction,Engineering Materials,Mechanical,Piping Design Basics

The heat-affected zone (HAZ) is an area generated when a metal is subjected to very high temperatures (Example: Welding, Mechanical Cutting, Laser Cutting, Plasma Cutting, etc). This is the non-melted zone near the exact worked area. The mechanical properties of the heat-affected zone are altered due to being exposed to high temperatures. So, the heat-affected zone or HAZ can be defined as the area between the melted metal and the base metal where microstructural changes occur. Refer to the Fig. 1 below:

Heat Affected Zone
Fig. 1: Explanation of Heat-Affected Zone

As can be seen from the above figure, while welding four distinct zones are created. Fusion Zone or FZ, Weld Interface, Heat Affected Zone or HAZ, and Unaffected Base Metal Zone.

The Fusion zone is a mixture of molten metal and filler metal. Next, the narrow mushy zone consisting of partially melted metal is the weld interface. The next region that suffers a peak temperature below the melting point temperature creating microstructural changes is known as the heat-affected zone. The parameters that decide the extent of microstructural changes are

  • Amount of heat input
  • Maximum temperature reached
  • Duration of elevated temperature, and
  • the cooling rate

A heat-affected zone weakens the metal by reducing its mechanical strength and is the weakest section in a weldment. Depending on various factors like material properties, heat concentration, intensity, welding, or metal cutting process, the HAZ area can vary in size and severity. The nomenclature of zones and boundaries in the heat-affected zone is shown in Fig. 2.

Zones and boundaries in the heat affected zone
Fig. 2: Zones and boundaries in the heat-affected zone

Causes of Heat-Affected Zone

The amount of heat input during the welding or cutting process normally exceeds the melting temperature and subsequent cooling leads to microstructural changes. Thermal diffusivity is the single most important factor influencing the size of the heat-affected zone. The level of thermal diffusivity is dependent on the metals:

Materials with high thermal diffusivity are capable of transferring the heat variation rapidly and cooling quicker, thus reducing the heat-affected zone width. On the contrary, materials with a lower thermal diffusivity coefficient retain the heat and the HAZ region becomes wider. Also, the duration of heat exposure has a direct impact on the HAZ region. When a metal is exposed to greater amounts of energy for longer periods the heat-affected zone is larger. With respect to the welding process the HAZ is dependent on:

  • Heat Input: Low heat input will cool faster resulting in a smaller HAZ.
  • Cooling Rate: Slower cooling rate will increase the size of the HAZ.
  • Welding Speed: Faster welding speed will reduce the HAZ area.
  • Welding Geometry: Weld geometry affects the heat sink. A smaller heat sink leads to slower cooling means larger HAZ.

In a similar way, the heat-affected zone for high-temperature cutting operations is also influenced by

  • the temperatures during cutting
  • speed of cutting operation.
  • cutting process
    • Shearing and waterjet cutting: No HAZ formation
    • Laser cutting: A smaller HAZ
    • Plasma cutting: An intermediate HAZ
    • Oxyacetylene cutting: The widest HAZ
  • the material properties, and thickness.

Effects of Heat-Affected Zones

Due to the heat experienced in the heat-affected zone, major undesirable microstructural changes occur that impacts the metal in various way as listed below:

  • Lower Strength
  • Residual Stress
  • Lower toughness
  • Reduced Corrosion Resistance
  • Susceptibility to cracking
  • Hydrogen embrittlement
  • Phase Change
  • Oxidation
  • Surface Nitriding
  • Localized Hardening

All these factors normally weaken the material creating challenges for the use of that material during the design of components.

Heat Affected Zone Area and Heat Tint Colors

During the welding or cutting, distinct HAZ areas are formed by the use of different temperatures in the base metal. A series of visible colored bands are generated known as heat tints. They are caused by the surface oxidation process specifically in stainless steel. However, these temperatures causing the ‘temper colors’ are much lower temperatures than those which form the heat-affected zone. Also, these color bands can extend for some distance beyond the actual heat-affected zone. These different colors vary from light yellow to dark blue and provide an approximate indication of the metal temperature reached. The following table provides the band colors with respect to temperatures:

ColorWelding/Cutting temperature
Light yellow290º C
Straw yellow340º C
Yellow370º C
Brown390º C
Purple brown420º C
Dark purple450º C
Blue540º C
Dark blue600º C
Table 1: Color Tint with respect to temperature

The parameters that affect the formation of these colored heat tints in the heat-affected zone are:

  • The material’s resistance to oxidation
  • Chromium content
  • Surface Condition
  • Extend of impurities on the surface
  • Presence of surface paints, oils, fingerprints, etc.

However, note that these heat tints do not impact the extent of the heat-affected zone.

Reduction of HAZ formation

Reducing the effect of the heat-affected zone can alleviate problems like corrosion, cracks, embrittlement, etc. These will make the component much stronger. Ideally, by selecting proper welding and cutting operation, the heat-affected zone should be minimized. But it may not be always possible to reduce the HAZ to the extent required. Hence, various methods can be applied to reduce the heat-affected zone as mentioned below:

  • Heat Treatment: Heat treatment is the best method to reduce the impacts of HAZ. Depending on the required mechanical/metallurgical properties and intended changes heat treatment process following the welding or cutting is selected. Based on the material a precipitation hardening and softening treatment can be applied.
  • Cutting the Heat-Affected Zone: Sometimes, cutting and grinding can be used to reduce the HAZ area.
  • Machining the HAZ: Machining to remove the heat-affected zone is also an effective method to reduce the impact.
  • Colored Heat tints can be easily removed with fine sandpaper or by grinding.

Heat-Affected Zone Distance

Calculation of heat-affected zone distance or width is not straightforward and very difficult. However, a simplified equation as provided in Fig. 3 below can be used for estimating HAZ distance/width for welding thin plates.

Heat Affected Zone Distance
Fig. 3: Heat-Affected Zone Distance

The above formula can be used to calculate the heat-affected zone distance. By knowing the peak temperature of the HAZ zone, the distance y can be calculated from the fusion line for welding a thin plate. Fig. 4 below provides a sample problem calculation regarding the same (Equation 4 mentioned in the answers is the equation shown in Fig. 3)

Sample calculation of Heat Affected Zone Distance
Fig. 4: Sample calculation of Heat Affected Zone Distance

Brittle Fracture and Ductile Fracture: Definition, Mechanism, Differences

Written by Anup Kumar Dey in Civil,Engineering Materials,Mechanical,Piping Stress Analysis,Piping Stress Basics

A fracture can be defined as the separation of the material into two or more parts. Failure of material can involve any of the two mechanisms; ductile fracture or brittle fracture. Both these fracture mechanisms in metal are distinct and different from each other. In this article, we will explore both of these failure mechanisms in detail.

What is Brittle Fracture or Brittle Failure?

Brittle fracture is the sudden and rapid metal failure in which the material shows little or no plastic strain. This is characterized by quick failure without any warning. The generated cracks propagate rapidly and the material collapses all of a sudden.

Brittle Fracture is a condition that occurs when a material is subjected to temperatures that make it less resilient, and therefore more brittle. The potential for material to become brittle depends on the type of material that is subjected to these low temperatures. Some materials, such as carbon and low alloy steels will become brittle at low temperatures and therefore susceptible to damage ranging from cracking to shattering or disintegration of equipment.

When a material becomes brittle, the consequences can be very serious. If the brittle material is subjected to an impact or an equivalent shock (ex. rapid pressurization) the combination could potentially lead to a catastrophic failure under certain conditions.

What is Ductile Fracture or Ductile Failure?

Ductile fracture is the material failure that exhibits substantial plastic deformation prior to fracture. The ductile fracture process is slow and gives enough warnings before final separation. Normally, a large amount of plastic flow is concentrated near the fracture faces.

The ductile fracture occurs over a period of time and normally occurs after yield stress, whereas brittle fracture is fast and can occur at lower stress levels than a ductile fracture. That is why Ductile fracture is considered better than brittle fracture. Refer to Fig. 1 below that explains both fracture mechanisms. The area under the stress-strain curve represents the absorbed energy before failure. Clearly, the required energy in brittle failure is quite less than the ductile failure.

Brittle vs Ductile Fracture
Fig. 1: Brittle vs Ductile Fracture

Brittle Fracture Mechanism

The mechanism of brittle fracture shown above is known as Brittle cleavage fracture. This occurs in metals with a high strain-hardening rate and relatively low cleavage strength.

Ductile materials under some conditions can become brittle if the conditions are changed. Such a condition is the effect of temperature. Many materials of industrial use exhibit ductile fracture at ambient and elevated temperatures and brittle fracture at low temperatures. The transition temperature below which a material is brittle and above which it is ductile is known as the Nil-Ductility Transition (NDT) temperature. This temperature is not constant but varies depending on prior mechanical and heat treatment and the nature and amounts of impurity elements. It is determined by the Izod or Charpy Impact tests. At temperature above the NDT temperature, some plastic deformation will occur before the fracture

With an increase in ductility, NDT decreases. So it is always preferred to increase ductility. The parameters that impact ductility are:

  • Grain Size: small grain sizes increase ductility and grain size is controlled by heat treatment.
  • Alloying Element: The addition of alloying elements can decrease grain size and thus decrease brittleness shifting the NDT to a lower temperature.

Cyclic stresses should be avoided for brittle materials. So, systems having thermal and pressure cycles should not be designed from brittle materials.

Causes of Brittle Fracture

The main concern with a brittle fracture or brittle failure is that under certain conditions failure occurs at stresses well below the yield strength. Such conditions are the presence of a flaw or crack. Brittle fractures are normally initiated by defects present in the manufactured product or fabricated structure or by defects that develop during service. These are basically stress concentrators and may take the form of.

  • Notches- discontinuities caused by abrupt changes in the direction of a free surface, often fracture initiators. Examples: sharp fillets, corners, holes, threads, splines, keyways, dents, gouges, or scratches.
  • Laps, folds, flakes, large inclusions, forging bursts, laminations, and undesirable grain.
  • Segregation, inclusions, undesirable microstructures, porosity, tears, cracks, or surface discontinuities are introduced during melting, deoxidation, grain refining, and casting operations.
  • Cracks resulting from machining, quenching, fatigue, hydrogen embrittlement, liquid metal embrittlement, or stress corrosion.
  • Residual stresses.

Brittle fracture normally occurs because of the propagation of such cracks at great speed. Smaller grain size, higher temperature, and lower stress tend to mitigate crack initiation. On the contrary, larger grain sizes, lower temperatures, and higher stress favor crack propagation. There is a stress level known as the lower fracture propagation stress below which a crack will not propagate at any temperature. With the increase in temperature, higher stress is required for a crack to propagate. A crack arrest curve defines the relationship between the temperature and the stress required for a crack to propagate.

Fracture Toughness

The amount of stress required to propagate a preexisting crack is indicated by the Fracture Toughness which depends on various factors mentioned below:

  • Metal composition
  • Metal temperature
  • The extent of deformations to the crystal structure
  • Metal grain size
  • Metal crystalline form
  • Flaw size

Refer to Fig. 2 below that represents fracture initiation curves for steel for various flaw sizes at various stresses and temperatures.

Fracture Initiation Curve at various Flaw Sizes
Fig. 2: Fracture Initiation Curve at various Flaw Sizes

From the above curve, it is evident that to avoid brittle fracture operating temperature should be maintained above NDT temperature. Maintaining the operating temperature above FTE temperature (NDT + 60°F for steel) will ensure greater safety.

Griffith’s Theory of Brittle Fracture

Consider a thin plate of length l having a thru-crack of length 2c, as shown in Fig 3. The upper curve shows the force-deflection curve for a non-extending crack of length 2c. For a non-extending crack of length 2(c + Δc), the curve will be the lower curve. The area between these two curves represents the energy released to extend the crack from 2c to 2(c + Δc).

Explanation of Griffith Theory of Brittle Fracture
Fig. 3: Explanation of Griffith’s Theory of Brittle Fracture

Using elasticity theory Griffith showed that the energy released per unit thickness during a crack growth of 2Δc is

Thus, the critical stress is inversely proportional to c½. Hence, the smaller the flaw, the greater the value of σc. The Griffith theory is good for every brittle material like glass, in which failure occurs without any plastic deformation. When there is some plastic deformation associated with
the crack extension, we must add the plastic work γp expended in making the surface to the surface energy term γs to obtain σc as shown below:

The above equation forms the starting point of modern fracture mechanics.

Mechanism of Ductile Fracture

Ductile fracture or ductile failure (Fig. 4) normally occurs following the below-mentioned steps:

(a) Necking
(b) Formation of microvoids
(c) Coalescence of microvoids to form a crack
(d) Crack propagation by shear deformation
(e) Fracture

Ductile Fracture Mechanism
Fig. 4: Ductile Fracture Mechanism

Brittle Fracture vs Ductile Fracture

From the above discussions, it is clear that the brittle fracture and ductile fracture mechanism is completely different. The major differences between brittle and ductile fracture are provided below:

Brittle Fracture / Brittle FailureDuctile Fracture / Ductile Failure
Negligible plastic deformationConsiderable plastic deformation.
Rapid and Quick Failure without any warningSlow process with sufficient warnings
Quick Crack propagationSlow crack propagation
Brittle fracture can occur below the yield strengthDuctile Failure normally occurs above yield strength.
In brittle fractures, the crack propagation is perpendicular to the applied stress. Crack propagation is at 45 Degrees to the applied stress.
Cleavage failureCup cone failure
Less energy requirement to failureThe energy required to fail is substantially high
It May Break into several piecesBroke into two pieces
Brittle Fracture vs Ductile Fracture