The purpose of this document is to provide guidance on the minimum necessary for working on joints, seals, etc. while the equipment is under pressure.

As part of the normal maintenance function at a facility, it is sometimes necessary to do mechanical work on joints, seals, etc. while that piece of equipment remains under pressure. Those activities may be done while the equipment remains pressurized if:

  • Adequate safeguards are practical and can be provided
  • A work permit and safety checklist has been approved by the unit maintenance and operations supervisors

It is the intent of this document that:

  • Failure of the bolt being worked on will not cause a gross failure of the flanged joint or seal
  • The quality, properties, pressure, and materials associated with threaded joints, tubing joints, or joints containing brittle materials can be adequately guarded against, should a gross failure of the joint occur
  • Limitations will be placed on types of tools and tightening procedures of joints in which either use history, environment, or material may result in brittle failure of structural portions of the joint during tightening
  • To provide specific guidance on “Hot Bolting” flanged joints prior to performing maintenance

Planning and Preparation

1. Authorization

A work permit is required, along with a completed Safety Checklist, before any tightening of joints is done under pressure. The work should be approved by the unit maintenance and operations supervisor (or higher) by signing off on the completed checklist.

2. Job Environment

The work area around the equipment to be tightened must provide adequate room for people to work, good footing, and unobstructed access and egress. This evaluation should be made based on the PPE that will be worn during the work. The equipment must be located such that the work can be performed without having potential leaks from the joint dripping on the workers. Steps must be taken to direct liquid and fumes from process material away from people working on the equipment. Fire or toxicity hazards must be addressed by containment, ventilation, diking, dilution, etc.

3. Process Material

When determining the feasibility of working on equipment under pressure, process material properties such as toxicity, flammability, corrosivity, and temperature must be taken into consideration. These must also be considered when specifying appropriate PPE for the task.

4. Materials of Construction

Materials of construction for all parts of the joint must be identified. Limitations area imposed on working on joints which contain cast iron, malleable iron, glass, Haveg (non metallic pipe material used in acid service, specifically in Sulfuric Acid) carbon, graphite, ceramic, plastic, or other brittle material in the structural or sealing portions of the joint.

5. Joint Failure

Consideration must be given to the consequences of a complete joint failure, such an injury to those working on the joint, fire, explosion, fume release, product loss, or damage to nearby equipment.

6. Operating Conditions

Operating temperature and pressure must be determined prior to starting work on the joint so that the maximum safe pressure for doing work can be calculated. These conditions should be monitored throughout the work to ensure that safe levels are not exceeded at any time.

7. Job Review

The procedure to be used to tighten the joint and all safety precautions should be reviewed with those performing the work prior to starting work. The review should include a copy of the work permit and the completed checklist.

Limitations on Working on Joints Under Pressure

1. Joints That Cannot Be Worked On Under Pressure

  • Joints subject to shock loading or impact loading, such as compressor cylinder head bolting
  • Bolted clamp union joints such a "Grayloc"
  • Bolted flange joints with less than 4 bolts

2. Impact Tools and Hammer Wrenches

Impact tools and hammer wrenches should not be used on joints at temperatures below 0 degrees C, or on joints that contain brittle materials in structural parts.

3. Brittle or Unknown Materials

Joints containing brittle materials or unknown materials may be worked on under pressure only when all of the following conditions are met:

  • Joints are not larger than 3/4" nominal size
  • Process material is not flammable, explosive, toxic, or corrosive
  • Operating temperature is below 55 degrees C
  • Operating pressure is 150 psig or below

4. Threaded Joints

Requires same conditions as Section "Brittle or Unknown Materials" above.

5. Tube Fitting Joints

Requires same conditions as Section "Brittle or Unknown Materials" above.

6. Standard Flanged Joints

Joints which consist of ANSI standard flanges bolted together may be worked on when the joint is subjected to pressures below the Maximum Operating Pressure. The Maximum Operating Pressure for a particular joint is based on the design pressure of the joint as determined by the flange rating, the material of construction, the operating temperature, and the number of bolts in the flange.

Number of Bolts Maximum Operating Pressure
1, 2, 3, 4 0 psig
6 5/8 of Design Pressure
8 3/4 of Design Pressure
10, 12 7/8 of Design Pressure
14 or more Full Design Pressure

7. Nonstandard Flanged Joints

Non-standard flanged joints such as hydraulic flanges, heat exchanger flanges, etc. may be tightened when the joint is subjected to pressures that are below the Maximum Operating Pressure. The Maximum Operating Pressure should be determined by using the table above and using the design temperature listed on the equipment drawing.

An engineering evaluation should be conducted by a knowledgeable engineer before a lower operating temperature can be used to change the Maximum Operating Pressure.

8. Packing Glands

Packing glands such as those found on pump shafts and valve stems are designed to be routinely tightened under full design pressure. If the gland is in good structural condition and the leak does not constitute a hazard to personnel tightening the packing, this work is exempt from the requirements of this guideline. Tightening on packing glands will require authorization under this procedure if 1) structural deterioration is evident, or 2) the process material is toxic, flammable, corrosive, or explosive.

9. Valve Bonnets

Valve bonnets should follow the same tightening requirements as for flanged connections. The valve plug should be "unseated" prior to tightening to ensure that undue stress is not placed on the stem, bonnet, and packing gland.

Removal of bolts from flanges without replacement “Hot Bolting”

Four and six bolt flanges – Bolts must not be removed from the flanges until the line break requirements have been met.

Flanges with eight or more bolts – When flanges contain eight or more bolts every other bolt may be removed without replacement provided the line break requirements have been met.

Flanges with fourteen or more bolts – When flanges contain fourteen or more bolts, two adjacent bolts may be removed with one bolt remaining between sets of removed bolting provided the line break requirements have been met.

Other Considerations

Tools - Because there is a 20% safety factor based on ultimate strength on bolting when tightening with a Biach Tensioner, hand wrench, or torque multiplier, these should be considered the standard equipment used in working on pressurized joints.

If the use of impact or hammer wrenches for tightening joints is required, it must be approved by supervision and noted on the safety checklist.